Human glyoxalase I. In Enzymology, a lactoylglutathione lyase ( (also known as glyoxalase I) is an Enzyme that catalyzes the Isomerization of Two zinc ions that are needed for the enzyme to catalyze its reaction are shown as purple spheres, and an enzyme inhibitor called S-hexylglutathione is shown as a space-filling model, filling the two active sites. Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. Space-filling models (also known as calotte models or CPK models by Corey, Pauling and Koltun like Ball-and-stick models belong

Enzymes are biomolecules that catalyze (i. A biomolecule is any organic Molecule that is produced by living Organisms including large Polymeric molecules such as Proteins Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst e. increase the rates of) chemical reactions. The reaction rate or rate of reaction for a Reactant or product in a particular reaction is intuitively defined as how fast a reaction takes A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called ^[1][2] Almost all enzymes are proteins. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Almost all processes in a biological cell need enzymes in order to occur at significant rates. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Since enzymes are extremely selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. In Biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell.

Like all catalysts, enzymes work by lowering the activation energy (E_a or ΔG^‡) for a reaction, thus dramatically increasing the rate of the reaction. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions. ^[3] A few RNA molecules called ribozymes catalyze reactions, with an important example being some parts of the ribosome. Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that ^[4][5] Synthetic molecules called artificial enzymes also display enzyme-like catalysis. An artificial enzyme is a synthetic organic molecule prepared to recreate the active site of an enzyme ^[6]

Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. Enzyme activators are molecules that bind to Enzymes and increase their activity Many drugs and poisons are enzyme inhibitors. A drug, broadly speaking is any chemical substance that when absorbed into the body In the context of Biology, poisons are substances that can cause damage, Illness, or Death to Organisms usually by Activity is also affected by temperature, chemical environment (e. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature g. pH), and the concentration of substrate. pH is the measure of the acidity or alkalinity of a Solution. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance Some enzymes are used commercially, for example, in the synthesis of antibiotics. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa In addition, some household products use enzymes to speed up biochemical reactions (e. g. , enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew). Laundry detergent, or washing powder, is a substance which is a type of Detergent that is added when one is washing Laundry to help get the laundry cleaner Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water A meat tenderizer can refer to a tool or a chemical used for tenderizing Meat.

Etymology and history

Eduard Buchner

As early as the late 1700s and early 1800s, the digestion of meat by stomach secretions^[7] and the conversion of starch to sugars by plant extracts and saliva were known. Eduard Buchner (May 20 1860 &ndash August 13 1917 was a German chemist and zymologist, the winner of the 1907 Nobel Prize in Chemistry In modern English usage meat most often refers to Animal tissue used as food mostly Skeletal muscle and associated Fat, but it may also refer Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. For the band see Saliva (band; for the village in Azerbaijan see Səliva. However, the mechanism by which this occurred had not been identified. ^[8]

In the 19th century, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur came to the conclusion that this fermentation was catalyzed by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms. Fermentation in Food processing typically refers to the conversion of Sugar to Alcohol using Yeast under Anaerobic conditions In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described Louis Pasteur (27 December 1822 – 28 September 1895 a French Chemist and Microbiologist, is best known for remarkable breakthroughs in the causes and Vitalism, as defined by the Merriam-Webster dictionary is a doctrine that the functions of a living organism are due to a vital principle distinct from physicochemical He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells. "^[9]

In 1878 German physiologist Wilhelm Kühne (1837–1900) first used the term enzyme, which comes from Greek ενζυμον "in leaven", to describe this process. Wilhelm Kühne ( March 28, 1837 - June 10, 1900) German Physiologist, was born in Hamburg. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly The word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment used to refer to chemical activity produced by living organisms. Pepsin is a digestive Protease ( released by the chief cells in the Stomach that functions to degrade food Proteins into

In 1897 Eduard Buchner began to study the ability of yeast extracts that lacked any living yeast cells to ferment sugar. Eduard Buchner (May 20 1860 &ndash August 13 1917 was a German chemist and zymologist, the winner of the 1907 Nobel Prize in Chemistry In a series of experiments at the University of Berlin, he found that the sugar was fermented even when there were no living yeast cells in the mixture. For other universities in Berlin see List of Universities in Berlin. ^[10] He named the enzyme that brought about the fermentation of sucrose "zymase". Zymase is an Enzyme complex ("mixture" that catalyzes Glycolysis, the fermentation of Sugar into Ethanol and Carbon ^[11] In 1907 he received the Nobel Prize in Chemistry "for his biochemical research and his discovery of cell-free fermentation". The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. Following Buchner's example; enzymes are usually named according to the reaction they carry out. Typically the suffix -ase is added to the name of the substrate (e. g. , lactase is the enzyme that cleaves lactose) or the type of reaction (e. Lactase (LCT a part of the β-galactosidase family of Enzymes is a Glycoside hydrolase involved in the Hydrolysis Lactose (also referred to as milk sugar) is a Sugar which is found most notably in Milk. g. , DNA polymerase forms DNA polymers). A DNA Polymerase is an Enzyme that assists in DNA replication.

Having shown that enzymes could function outside a living cell, the next step was to determine their biochemical nature. Many early workers noted that enzymatic activity was associated with proteins, but several scientists (such as Nobel laureate Richard Willstätter) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis. Richard Martin Willstätter ( August 13, 1872 – August 3, 1942) was a German Organic chemist whose study of the structure However, in 1926, James B. Sumner showed that the enzyme urease was a pure protein and crystallized it; Sumner did likewise for the enzyme catalase in 1937. James Batcheller Sumner ( November 19, 1887 &ndash August 12, 1955) was an American Chemist. Urease ( is an Enzyme that catalyzes the Hydrolysis of Urea into Carbon dioxide and Ammonia. Catalase is a common Enzyme found in nearly all living organisms where it functions to catalyze the decomposition of Hydrogen peroxide to The conclusion that pure proteins can be enzymes was definitively proved by Northrop and Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. John Howard Northrop ( July 5 1891 &ndash May 27 1987) was an American biochemist who won the Nobel Prize in Chemistry Wendell Meredith Stanley ( August 16, 1904 &ndash June 15, 1971) was an American biochemist, virologist These three scientists were awarded the 1946 Nobel Prize in Chemistry. ^[12]

This discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. X-ray crystallography is a method of determining the arrangement of Atoms within a Crystal, in which a beam of X-rays strikes a crystal and scatters This was first done for lysozyme, an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965. Lysozyme is a family of Enzymes ( which damage bacterial cell walls by catalyzing Hydrolysis of 14-beta-linkages between N-acetylmuramic acid and Albumen redirects here For other uses see Albumen (disambiguation. David Chilton Phillips Baron Phillips of Ellesmere, KBE, FRS ( 7 March 1924 - 23 February 1999) is considered to be a founding ^[13] This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail. Structural biology is the branch of Molecular biology concerned with the Architecture and shape of biological Macromolecules especially Proteins

Structures and mechanisms

See also: Enzyme catalysis

Ribbon-diagram showing carbonic anhydrase II. Enzyme catalysis is the Catalysis of Chemical reactions by specialized Proteins known as Enzymes. The carbonic anhydrases (or carbonate dehydratases) form a family of Enzymes that catalyze the rapid conversion of Carbon dioxide to Bicarbonate The grey sphere is the zinc cofactor in the active site. Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Diagram drawn from PDB 1MOO.

Enzymes are generally globular proteins and range from just 62 amino acid residues in size, for the monomer of 4-oxalocrotonate tautomerase,^[14] to over 2,500 residues in the animal fatty acid synthase. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other 4-Oxalocrotonate tautomerase (EC 532-4-OT is an enzyme that converts 2-hydroxymuconate to the αβ-unsaturated ketone 2-oxo-3-hexenedioate Fatty acid synthase (FAS is Enzymatic system composed of 272 kDa multifunctional Polypeptide, in which Substrates are handed from one functional domain ^[15] A small number of RNA-based biological catalysts exist, with the most common being the ribosome, these are either referred to as RNA-enzymes, or ribozymes. Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes The activities of enzymes are determined by their three-dimensional structure. In Biochemistry, quaternary structure is the arrangement of multiple folded Protein molecules in a multi-subunit complex ^[16] Most enzymes are much larger than the substrates they act on, and only a small portion of the enzyme (around 3–4 amino acids) is directly involved in catalysis. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this ^[17] The region that contains these catalytic residues, binds the substrate, and then carries out the reaction is known as the active site. The active site of an Enzyme contains the catalytic and Binding sites. Enzymes can also contain sites that bind cofactors, which are needed for catalysis. A cofactor is a non-protein Chemical compound that is bound (either tightly or loosely to an Enzyme and is required for Catalysis. Some enzymes also have binding sites for small molecules, which are often direct or indirect products or substrates of the reaction catalyzed. This binding can serve to increase or decrease the enzyme's activity, providing a means for feedback regulation. Feedback is a circular causal Process whereby some proportion of a system's output is returned (fed back to the Input.

Like all proteins, enzymes are made as long, linear chains of amino acids that fold to produce a three-dimensional product. Protein folding is the physical process by which a Polypeptide folds into its characteristic and functional three-dimensional structure. In Biochemistry and Chemistry, the tertiary structure of a Protein or any other Macromolecule is its three-dimensional structure as defined Each unique amino acid sequence produces a specific structure, which has unique properties. Individual protein chains may sometimes group together to form a protein complex. A protein complex is a group of two or more Proteins Protein complexes are a form of Quaternary structure. Most enzymes can be denatured—that is, unfolded and inactivated—by heating or chemical denaturants, which disrupt the three-dimensional structure of the protein. Denaturation is a process in which Proteins or Nucleic acids lose their structure (tertiary structure by application of some external stress or compound for In Biochemistry and Chemistry, the tertiary structure of a Protein or any other Macromolecule is its three-dimensional structure as defined Depending on the enzyme, denaturation may be reversible or irreversible.

Specificity

Enzymes are usually very specific as to which reactions they catalyze and the substrates that are involved in these reactions. Complementary shape, charge and hydrophilic/hydrophobic characteristics of enzymes and substrates are responsible for this specificity. Hydrophile, from the Greek (hydros "water" and φιλια (philia "friendship" refers to a physical property of a Molecule In Chemistry, hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) refers to the physical property of Enzymes can also show impressive levels of stereospecificity, regioselectivity and chemoselectivity. In Chemistry, stereospecificity is the property of a Chemical reaction that yields different stereoisomeric reaction products from two stereoisomeric In Chemistry, regioselectivity is the preference of one direction of Chemical bond making or breaking over all other possible directions. Chemical reactions are defined usually in small contexts (only up to a small number of neighbouring atoms such generalizations are a matter of utility ^[18]

Some of the enzymes showing the highest specificity and accuracy are involved in the copying and expression of the genome. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby These enzymes have "proof-reading" mechanisms. Here, an enzyme such as DNA polymerase catalyzes a reaction in a first step and then checks that the product is correct in a second step. A DNA Polymerase is an Enzyme that assists in DNA replication. ^[19] This two-step process results in average error rates of less than 1 error in 100 million reactions in high-fidelity mammalian polymerases. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands ^[20] Similar proofreading mechanisms are also found in RNA polymerase,^[21] aminoacyl tRNA synthetases^[22] and ribosomes. RNA polymerase ( RNAP or RNApol) is an Enzyme that produces RNA. An aminoacyl tRNA synthetase ( aaRS) is an Enzyme that catalyzes the Esterification of a specific Amino acid or its precursor to one of all its compatible Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that ^[23]

Some enzymes that produce secondary metabolites are described as promiscuous, as they can act on a relatively broad range of different substrates. Secondary metabolites are Organic compounds that are not directly involved in the normal growth, development or Reproduction of Organisms It has been suggested that this broad substrate specificity is important for the evolution of new biosynthetic pathways. ^[24]

"Lock and key" model

Enzymes are very specific, and it was suggested by Emil Fischer in 1894 that this was because both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. Hermann Emil Fischer (9 October 1852 - 15 July 1919 was a German Chemist and recipient of the Nobel Prize for Chemistry in 1902 ^[25] This is often referred to as "the lock and key" model. However, while this model explains enzyme specificity, it fails to explain the stabilization of the transition state that enzymes achieve. The "lock and key" model has proven inaccurate and the induced fit model is the most currently accepted enzyme-substrate-coenzyme figure.

Induced fit model

Diagrams to show the induced fit hypothesis of enzyme action.

In 1958 Daniel Koshland suggested a modification to the lock and key model: since enzymes are rather flexible structures, the active site is continually reshaped by interactions with the substrate as the substrate interacts with the enzyme. Daniel Edward Koshland Jr (1920 - 23 July 2007) reorganized the study of biology at the University of California at Berkeley and was the editor of the ^[26] As a result, the substrate does not simply bind to a rigid active site, the amino acid side chains which make up the active site are moulded into the precise positions that enable the enzyme to perform its catalytic function. A side chain in Organic chemistry and Biochemistry is a part of a Molecule that is attached to a core structure In some cases, such as glycosidases, the substrate molecule also changes shape slightly as it enters the active site. ^[27] The active site continues to change until the substrate is completely bound, at which point the final shape and charge is determined. ^[28]

Mechanisms

Enzymes can act in several ways, all of which lower ΔG^‡:^[29]

• Lowering the activation energy by creating an environment in which the transition state is stabilized (e. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined g. straining the shape of a substrate - by binding the transition-state conformation of the substrate/product molecules, the enzyme distorts the bound substrate(s) into their transition state form, thereby reducing the amount of energy required to complete the transition).
• Lowering the energy of the transition state, but without distorting the substrate, by creating an environment with the opposite charge distribution to that of the transition state.
• Providing an alternative pathway. For example, temporarily reacting with the substrate to form an intermediate ES complex, which would be impossible in the absence of the enzyme.
• Reducing the reaction entropy change by bringing substrates together in the correct orientation to react. Considering ΔH^‡ alone overlooks this effect.

Interestingly, this entropic effect involves destabilization of the ground state,^[30] and its contribution to catalysis is relatively small. ^[31]

Transition State Stabilization

The understanding of the origin of the reduction of ΔG^‡ requires one to find out how the enzymes can stabilize its transition state more than the transition state of the uncatalyzed reaction. Apparently, the most effective way for reaching large stabilization is the use of electrostatic effects, in particular, by having a relatively fixed polar environment that is oriented toward the charge distribution of the transition state. ^[32] Such an environment does not exist in the uncatalyzed reaction in water.

Dynamics and function

Recent investigations have provided new insights into the connection between internal dynamics of enzymes and their mechanism of catalysis. ^[33][34][35] An enzyme's internal dynamics are the movement of its internal parts (e. g. amino acids, a group of amino acids, a loop region, an alpha helix, neighboring beta-sheets or even an entire domain) of these proteins. These movements occur at various time-scales ranging from femtoseconds to seconds. To help compare Orders of magnitude of different Times this page lists times between 10&minus15 second and 10&minus12 second (1 Femto Networks of protein residues throughout an enzyme's structure can contribute to catalysis through dynamic motions. ^{[36][37][38][39]} Protein motions are vital to many enzymes, but whether small and fast vibrations, or larger and slower conformational movements are more important depends on the type of reaction involved. However, although these movements are important in binding and releasing substrates and products, it is not clear if protein movements help to accelerate the chemical steps in enzymatic reactions. ^[40] These new insights also have implications in understanding allosteric effects and developing new drugs.

Allosteric modulation

Allosteric enzymes change their structure in response to binding of effectors. In Biochemistry, allosteric regulation is the regulation of an Enzyme or other Protein by binding an effector molecule at the protein's allosteric An effector is a molecule (originally referring to small molecules but now encompassing any regulatory molecule includes proteins that binds to a Protein and thereby alters Modulation can be direct, where the effector binds directly to binding sites in the enzyme, or indirect, where the effector binds to other proteins or protein subunits that interact with the allosteric enzyme and thus influence catalytic activity. In Biochemistry, a binding site is a region on a Protein, DNA, or RNA to which specific other Molecules and Ions &mdash In Structural biology, a protein subunit or subunit protein is a single Protein Molecule that assembles (or " coassembles "

Cofactors and coenzymes

Main articles: Cofactor (biochemistry) and Coenzyme

Cofactors

Some enzymes do not need any additional components to show full activity. A cofactor is a non-protein Chemical compound that is bound (either tightly or loosely to an Enzyme and is required for Catalysis. Coenzymes are small organic non- Protein Molecules that carry chemical groups between Enzymes Coenzymes are sometimes referred to as cosubstrates However, others require non-protein molecules called cofactors to be bound for activity. ^[41] Cofactors can be either inorganic (e. Traditionally inorganic compounds are considered to be of mineral not biological origin g. , metal ions and iron-sulfur clusters) or organic compounds, (e. For biological Fe-S clusters see Iron-sulfur proteins Iron-sulfur clusters are ensembles of Iron and Sulfide centres An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. g. , flavin and heme). For the town in France see Flavin Aveyron. Flavin (from Latin flavus, "yellow" is the common name for a group of Organic A heme ( American English) or haem ( British English) is a Prosthetic group that consists of an Iron atom contained in the center of Organic cofactors can be either prosthetic groups, which are tightly bound to an enzyme, or coenzymes, which are released from the enzyme's active site during the reaction. A prosthetic group is a non-protein (non- Amino acid) component of a Conjugated protein that is important in the protein's biological activity Coenzymes are small organic non- Protein Molecules that carry chemical groups between Enzymes Coenzymes are sometimes referred to as cosubstrates Coenzymes include NADH, NADPH and adenosine triphosphate. Nicotinamide adenine dinucleotide, abbreviated NAD+, is a Coenzyme found in all living cells The compound is a dinucleotide since it consists Nicotinamide adenine dinucleotide phosphate ( NADP+, in older notation triphosphopyridine nucleotide TPN) is used in anabolic reactions such as Lipid Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy These molecules act to transfer chemical groups between enzymes. ^[42]

An example of an enzyme that contains a cofactor is carbonic anhydrase, and is shown in the ribbon diagram above with a zinc cofactor bound as part of its active site. The carbonic anhydrases (or carbonate dehydratases) form a family of Enzymes that catalyze the rapid conversion of Carbon dioxide to Bicarbonate ^[43] These tightly-bound molecules are usually found in the active site and are involved in catalysis. For example, flavin and heme cofactors are often involved in redox reactions. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state

Enzymes that require a cofactor but do not have one bound are called apoenzymes or apoproteins. An apoenzyme together with its cofactor(s) is called a holoenzyme (this is the active form). Most cofactors are not covalently attached to an enzyme, but are very tightly bound. However, organic prosthetic groups can be covalently bound (e. g. , thiamine pyrophosphate in the enzyme pyruvate dehydrogenase). Thiamine pyrophosphate (TPP or thiamine diphosphate (ThDP is a Thiamine derivative which is cleaved by Thiamine pyrophosphatase. Pyruvate dehydrogenase (E1 is the first component Enzyme of Pyruvate dehydrogenase complex (PDC

Coenzymes

Space-filling model of the coenzyme NADH

Coenzymes are small organic molecules that transport chemical groups from one enzyme to another. Molecular graphics ( MG) is the discipline and philosophy of studying Molecules and their properties through graphical representation ^[44] Some of these chemicals such as riboflavin, thiamine and folic acid are vitamins, this is when these compounds cannot be made in the body and must be acquired from the diet. Riboflavin ( E101) also known as vitamin B2, is an easily absorbed Micronutrient with a key role in maintaining Health For the similarly spelled pyrimidine see Thymine Thiamin or thiamine, also known as Vitamin B1 Folic acid (also known as Vitamin M and Folacin) and Folate (the Anionic form are forms of the water-soluble Vitamin B9 A vitamin is an Organic compound required as a Nutrient in tiny amounts by an Organism. The chemical groups carried include the hydride ion (H^-) carried by NAD or NADP⁺, the acetyl group carried by coenzyme A, formyl, methenyl or methyl groups carried by folic acid and the methyl group carried by S-adenosylmethionine. Hydride is the name given to the negative Ion of Hydrogen, H− Nicotinamide adenine dinucleotide, abbreviated NAD+, is a Coenzyme found in all living cells The compound is a dinucleotide since it consists Coenzyme A ( CoA, CoASH, or HSCoA) is a Coenzyme, notable for its role in the synthesis and oxidation of Fatty acids Folic acid (also known as Vitamin M and Folacin) and Folate (the Anionic form are forms of the water-soluble Vitamin B9 S -Adenosyl methionine (SAM is a Coenzyme involved in Methyl group transfers

Since coenzymes are chemically changed as a consequence of enzyme action, it is useful to consider coenzymes to be a special class of substrates, or second substrates, which are common to many different enzymes. For example, about 700 enzymes are known to use the coenzyme NADH. ^[45]

Coenzymes are usually regenerated and their concentrations maintained at a steady level inside the cell: for example, NADPH is regenerated through the pentose phosphate pathway and S-adenosylmethionine by methionine adenosyltransferase. The pentose phosphate pathway (also called Phosphogluconate Pathway or HexoseMonophosphate Shunt shunt is a process that serves to generate NADPH and the synthesis of pentose

Thermodynamics

The energies of the stages of a chemical reaction. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Substrates need a lot of energy to reach a transition state, which then decays into products. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. The enzyme stabilizes the transition state, reducing the energy needed to form products.

Main articles: Activation energy, Thermodynamic equilibrium, and Chemical equilibrium

As all catalysts, enzymes do not alter the position of the chemical equilibrium of the reaction. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined In Thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium Mechanical equilibrium, and In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change Usually, in the presence of an enzyme, the reaction runs in the same direction as it would without the enzyme, just more quickly. However, in the absence of the enzyme, other possible uncatalyzed, "spontaneous" reactions might lead to different products, because in those conditions this different product is formed faster.

Furthermore, enzymes can couple two or more reactions, so that a thermodynamically favorable reaction can be used to "drive" a thermodynamically unfavorable one. For example, the hydrolysis of ATP is often used to drive other chemical reactions. Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy

Enzymes catalyze the forward and backward reactions equally. They do not alter the equilibrium itself, but only the speed at which it is reached. For example, carbonic anhydrase catalyzes its reaction in either direction depending on the concentration of its reactants. The carbonic anhydrases (or carbonate dehydratases) form a family of Enzymes that catalyze the rapid conversion of Carbon dioxide to Bicarbonate

(in tissues; high CO₂ concentration)

(in lungs; low CO₂ concentration)

Nevertheless, if the equilibrium is greatly displaced in one direction, that is, in a very exergonic reaction, the reaction is effectively irreversible. Tissue is a cellular organizational level intermediate between cells and a complete organism lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive Exergonic means to release energy in the form of work Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon meaning work, Under these conditions the enzyme will, in fact, only catalyze the reaction in the thermodynamically allowed direction.

Kinetics

Main article: Enzyme kinetics

Mechanism for a single substrate enzyme catalyzed reaction. Enzyme kinetics is the study of the Chemical reactions that are catalysed by Enzymes, with a focus on their Reaction rates The study of The enzyme (E) binds a substrate (S) and produces a product (P).

Enzyme kinetics is the investigation of how enzymes bind substrates and turn them into products. The rate data used in kinetic analyses are obtained from enzyme assays. Enzyme assays are Laboratory methods for measuring enzymatic activity

In 1902 Victor Henri^[46] proposed a quantitative theory of enzyme kinetics, but his experimental data were not useful because the significance of the hydrogen ion concentration was not yet appreciated. Prince Jacques-Victor Henry ( 3 March 1804 - 18 October 1820) was the Heir apparent to the throne of the Kingdom of Haiti. After Peter Lauritz Sørensen had defined the logarithmic pH-scale and introduced the concept of buffering in 1909^[47] the German chemist Leonor Michaelis and his Canadian postdoc Maud Leonora Menten repeated Henri's experiments and confirmed his equation which is referred to as Henri-Michaelis-Menten kinetics (sometimes also Michaelis-Menten kinetics). Leonor Michaelis ( January 16, 1875 &ndash October 8, 1949) was a German Biochemist and Physician famous for Maud Leonora Menten ( March 20, 1879 &ndash July 26, 1960) was a Canadian medical scientist who made significant contributions to ^[48] Their work was further developed by G. E. Briggs and J. B. S. Haldane, who derived kinetic equations that are still widely used today. George Edward Briggs ( 25 June 1893 - 7 February 1985) was a British botanist John Burdon Sanderson Haldane FRS ( 5 November 1892 &ndash 1 December 1964) known as Jack (but who used 'J ^[49]

The major contribution of Henri was to think of enzyme reactions in two stages. In the first, the substrate binds reversibly to the enzyme, forming the enzyme-substrate complex. This is sometimes called the Michaelis complex. The enzyme then catalyzes the chemical step in the reaction and releases the product.

Saturation curve for an enzyme reaction showing the relation between the substrate concentration (S) and rate (v).

Enzymes can catalyze up to several million reactions per second. For example, the reaction catalyzed by orotidine 5'-phosphate decarboxylase will consume half of its substrate in 78 million years if no enzyme is present. Orotidine 5'-phosphate decarboxylase is an Enzyme involved in Pyrimidine metabolism However, when the decarboxylase is added, the same process takes just 25 milliseconds. ^[50] Enzyme rates depend on solution conditions and substrate concentration. Conditions that denature the protein abolish enzyme activity, such as high temperatures, extremes of pH or high salt concentrations, while raising substrate concentration tends to increase activity. To find the maximum speed of an enzymatic reaction, the substrate concentration is increased until a constant rate of product formation is seen. This is shown in the saturation curve on the right. Saturation happens because, as substrate concentration increases, more and more of the free enzyme is converted into the substrate-bound ES form. At the maximum velocity (V_max) of the enzyme, all the enzyme active sites are bound to substrate, and the amount of ES complex is the same as the total amount of enzyme. However, V_max is only one kinetic constant of enzymes. The amount of substrate needed to achieve a given rate of reaction is also important. This is given by the Michaelis-Menten constant (K_m), which is the substrate concentration required for an enzyme to reach one-half its maximum velocity. Each enzyme has a characteristic K_m for a given substrate, and this can show how tight the binding of the substrate is to the enzyme. Another useful constant is k_cat, which is the number of substrate molecules handled by one active site per second.

The efficiency of an enzyme can be expressed in terms of k_cat/K_m. This is also called the specificity constant and incorporates the rate constants for all steps in the reaction. In Chemical kinetics a reaction rate constant k or \lambda quantifies the speed of a Chemical reaction. Because the specificity constant reflects both affinity and catalytic ability, it is useful for comparing different enzymes against each other, or the same enzyme with different substrates. The theoretical maximum for the specificity constant is called the diffusion limit and is about 10⁸ to 10⁹ (M^-1 s^-1). At this point every collision of the enzyme with its substrate will result in catalysis, and the rate of product formation is not limited by the reaction rate but by the diffusion rate. Enzymes with this property are called catalytically perfect or kinetically perfect. A catalytically perfect enzyme or kinetically perfect enzyme is an Enzyme that catalyzes so efficiently that almost every time enzyme meets its substrate Example of such enzymes are triose-phosphate isomerase, carbonic anhydrase, acetylcholinesterase, catalase, fumarase, β-lactamase, and superoxide dismutase. Triose-phosphate isomerase (TPI or TIM is an Enzyme ( that catalyzes the reversible interconversion of the Triose phosphate Isomers The carbonic anhydrases (or carbonate dehydratases) form a family of Enzymes that catalyze the rapid conversion of Carbon dioxide to Bicarbonate Catalase is a common Enzyme found in nearly all living organisms where it functions to catalyze the decomposition of Hydrogen peroxide to The enzyme superoxide dismutase ( SOD,) catalyzes the Dismutation of Superoxide into Oxygen and Hydrogen peroxide.

Michaelis-Menten kinetics relies on the law of mass action, which is derived from the assumptions of free diffusion and thermodynamically-driven random collision. In chemistry Law of Mass Action has two aspects 1 the equilibrium aspect concerning the composition of a reaction mixture at equilibrium and 2 the kinetic Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement However, many biochemical or cellular processes deviate significantly from these conditions, because of very high concentrations, phase-separation of the enzyme/substrate/product, or one or two-dimensional molecular movement. ^[51] In these situations, a fractal Michaelis-Menten kinetics may be applied. A fractal is generally "a rough or fragmented geometric shape that can be split into parts each of which is (at least approximately a reduced-size copy of the whole" ^{[52][53][54][55]}

Some enzymes operate with kinetics which are faster than diffusion rates, which would seem to be impossible. Several mechanisms have been invoked to explain this phenomenon. Some proteins are believed to accelerate catalysis by drawing their substrate in and pre-orienting them by using dipolar electric fields. Other models invoke a quantum-mechanical tunneling explanation, whereby a proton or an electron can tunnel through activation barriers, although for proton tunneling this model remains somewhat controversial. In Quantum mechanics, quantum tunnelling is a nanoscopic phenomenon in which a particle violates the principles of Classical mechanics by penetrating a ^[56][57] Quantum tunneling for protons has been observed in tryptamine. Tryptamine is a Monoamine Alkaloid found in Plants and Animals. ^[58] This suggests that enzyme catalysis may be more accurately characterized as "through the barrier" rather than the traditional model, which requires substrates to go "over" a lowered energy barrier.

Inhibition

Competitive inhibitors bind reversibly to the enzyme, preventing the binding of substrate. On the other hand, binding of substrate prevents binding of the inhibitor. Substrate and inhibitor compete for the enzyme.

Types of inhibition. This classification was introduced by W. W. Cleland. ^[59]

Main article: Enzyme inhibitor

Enzyme reaction rates can be decreased by various types of enzyme inhibitors. Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity.

Competitive inhibition

In competitive inhibition, the inhibitor and substrate compete for the enzyme (i. e. , they can not bind at the same time). Often competitive inhibitors strongly resemble the real substrate of the enzyme. For example, methotrexate is a competitive inhibitor of the enzyme dihydrofolate reductase, which catalyzes the reduction of dihydrofolate to tetrahydrofolate. Dihydrofolate reductase, or DHFR, reduces Dihydrofolic acid to Tetrahydrofolic acid, using NADPH as Electron donor, which can be converted Folic acid (also known as Vitamin M and Folacin) and Folate (the Anionic form are forms of the water-soluble Vitamin B9 Folic acid (also known as Vitamin M and Folacin) and Folate (the Anionic form are forms of the water-soluble Vitamin B9 The similarity between the structures of folic acid and this drug are shown in the figure to the right bottom. Note that binding of the inhibitor need not be to the substrate binding site (as frequently stated), if binding of the inhibitor changes the conformation of the enzyme to prevent substrate binding and vice versa. In competitive inhibition the maximal velocity of the reaction is not changed, but higher substrate concentrations are required to reach a given velocity, increasing the apparent K_m.

Uncompetitive inhibition

In uncompetitive inhibition the inhibitor can not bind to the free enzyme, but only to the ES-complex. The EIS-complex thus formed is enzymatically inactive. This type of inhibition is rare, but may occur in multimeric enzymes.

Non-competitive inhibition

Non-competitive inhibitors can bind to the enzyme at the same time as the substrate, i. e. they never bind to the active site. Both the EI and EIS complexes are enzymatically inactive. Because the inhibitor can not be driven from the enzyme by higher substrate concentration (in contrast to competitive inhibition), the apparent V_max changes. But because the substrate can still bind to the enzyme, the K_m stays the same.

Mixed inhibition

This type of inhibition resembles the non-competitive, except that the EIS-complex has residual enzymatic activity.

In many organisms inhibitors may act as part of a feedback mechanism. Feedback is a circular causal Process whereby some proportion of a system's output is returned (fed back to the Input. If an enzyme produces too much of one substance in the organism, that substance may act as an inhibitor for the enzyme at the beginning of the pathway that produces it, causing production of the substance to slow down or stop when there is sufficient amount. This is a form of negative feedback. Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Enzymes which are subject to this form of regulation are often multimeric and have allosteric binding sites for regulatory substances. Their substrate/velocity plots are not hyperbolar, but sigmoidal (S-shaped).

The coenzyme folic acid (left) and the anti-cancer drug methotrexate (right) are very similar in structure. As a result, methotrexate is a competitive inhibitor of many enzymes that use folates.

Irreversible inhibitors react with the enzyme and form a covalent adduct with the protein. Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. The inactivation is irreversible. These compounds include eflornithine a drug used to treat the parasitic disease sleeping sickness. Eflornithine (α-difluoromethylornithine or DFMO is a drug manufactured by Sanofi-Aventis which has various uses Sleeping sickness or human African trypanosomiasis is a Parasitic Disease of people and animals caused by Protozoa of species ^[60] Penicillin and Aspirin also act in this manner. Penicillin (sometimes abbreviated PCN or pen) is a group of Beta-lactam antibiotics used in the treatment of Bacterial Infections Aspirin, or acetylsalicylic acid (ASA (əˌsɛtɨlsælɨˌsɪlɨk ˈæsɨd is a Salicylate drug, often used as an Analgesic to relieve With these drugs, the compound is bound in the active site and the enzyme then converts the inhibitor into an activated form that reacts irreversibly with one or more amino acid residues.

Uses of inactivators

Inhibitors are often used as drugs, but they can also act as poisons. However, the difference between a drug and a poison is usually only a matter of amount, since most drugs are toxic at some level, as Paracelsus wrote, "In all things there is a poison, and there is nothing without a poison. Paracelsus (11 November or 17 December 1493 in Einsiedeln Switzerland – 24 September 1541 in Salzburg, Austria) was an alchemist, "^[61] Equally, antibiotics and other anti-infective drugs are just specific poisons that kill a pathogen but not its host. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa In Biology, a host is an organism that harbors a Virus or Parasite, or a mutual or Commensal Symbiont, typically providing nourishment

An example of an inactivator being used as a drug is aspirin, which inhibits the COX-1 and COX-2 enzymes that produce the inflammation messenger prostaglandin, thus suppressing pain and inflammation. Aspirin, or acetylsalicylic acid (ASA (əˌsɛtɨlsælɨˌsɪlɨk ˈæsɨd is a Salicylate drug, often used as an Analgesic to relieve Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens A prostaglandin is any member of a group of Lipid compounds that are derived enzymatically from Fatty acids and have important functions in the Animal body The poison cyanide is an irreversible enzyme inactivator that combines with the copper and iron in the active site of the enzyme cytochrome c oxidase and blocks cellular respiration. A cyanide is any Chemical compound that contains the cyano group (C≡N which consists of a Carbon Atom triple-bonded to a The Enzyme cytochrome c oxidase or Complex IV () is a large Transmembrane protein complex found in Bacteria and the Mitochondrion Cellular respiration is the set of the metabolic reactions and processes that take place in Organisms cells to convert biochemical energy from ^[62]

Biological function

Enzymes serve a wide variety of functions inside living organisms. A function is part of an answer to a question about why some object or process occurred in a system that Evolved through a process of Selection. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases. In Biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another In Chemistry and Biochemistry, a kinase, alternatively known as a phosphotransferase, is a type of Enzyme that transfers Phosphate A phosphatase is an Enzyme that removes a Phosphate group from its Substrate by hydrolysing Phosphoric acid mono Esters into ^[63] They also generate movement, with myosin hydrolysing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton. Myosins are a large family of Motor proteins found in Eukaryotic tissues. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin cytoskeleton (also CSK is a cellular " Scaffolding " or " Skeleton " contained within the Cytoplasm. ^[64] Other ATPases in the cell membrane are ion pumps involved in active transport. "Ion pump" redirects here For pumps that reduce pressure see Ion pump (physics. Active transport is the mediated process of moving particles across Biological membrane against the concentration gradient Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies. Luciferase is a generic name for Enzymes commonly used in nature for Bioluminescence. FireFly is the second single by Essex Alternative rock band InMe. ^[65] Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable Integrase is an enzyme produced by a Retrovirus (including HIV) that enables its genetic material to be integrated into the DNA of the infected cell In Biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase Enzyme that transcribes Sialidase 1 (lysosomal sialidase, also known as NEU1 or neuraminidase, is a human Gene.

An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines. Amylase is an Enzyme that breaks Starch down into Sugar. Amylase is present in human Saliva, where it begins the chemical process A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Starch molecules, for example, are too large to be absorbed from the intestine, but enzymes hydrolyse the starch chains into smaller molecules such as maltose and eventually glucose, which can then be absorbed. Maltose, or malt sugar is a Disaccharide formed from two units of Glucose joined with an α(1→4 linkage Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Different enzymes digest different food substances. In ruminants which have a herbivorous diets, microorganisms in the gut produce another enzyme, cellulase to break down the cellulose cell walls of plant fiber. Physiologically a ruminant is a Mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first stomach known Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell Cellulase refers to a class of Enzymes produced chiefly by Fungi, Bacteria, and Protozoans that Catalyze the cellulolysis (or ^[66]

Several enzymes can work together in a specific order, creating metabolic pathways. In Biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme. Sometimes more than one enzyme can catalyze the same reaction in parallel, this can allow more complex regulation: with for example a low constant activity being provided by one enzyme but an inducible high activity from a second enzyme.

Enzymes determine what steps occur in these pathways. Without enzymes, metabolism would neither progress through the same steps, nor be fast enough to serve the needs of the cell. Indeed, a metabolic pathway such as glycolysis could not exist independently of enzymes. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized Glucose, for example, can react directly with ATP to become phosphorylated at one or more of its carbons. Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule In the absence of enzymes, this occurs so slowly as to be insignificant. However, if hexokinase is added, these slow reactions continue to take place except that phosphorylation at carbon 6 occurs so rapidly that if the mixture is tested a short time later, glucose-6-phosphate is found to be the only significant product. Variation across species Hexokinases have been found in every organism checked ranging from bacteria, Yeast, and Plants to humans and other Vertebrates Glucose 6-phosphate (also known as Robison ester) is Glucose sugar Phosphorylated on carbon 6 Consequently, the network of metabolic pathways within each cell depends on the set of functional enzymes that are present.

Control of activity

There are five main ways that enzyme activity is controlled in the cell.

1. Enzyme production (transcription and translation of enzyme genes) can be enhanced or diminished by a cell in response to changes in the cell's environment. Transcription is the synthesis of RNA under the direction of DNA Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) This form of gene regulation is called enzyme induction and inhibition. Gene modulation redirects here For information on therapeutic regulation of gene expression see Therapeutic gene modulation. Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. For example, bacteria may become resistant to antibiotics such as penicillin because enzymes called beta-lactamases are induced that hydrolyse the crucial beta-lactam ring within the penicillin molecule. Antibiotic resistance is the ability of a Microorganism to withstand the effects of Antibiotics. Penicillin (sometimes abbreviated PCN or pen) is a group of Beta-lactam antibiotics used in the treatment of Bacterial Infections Beta-lactamases are Enzymes ( produced by some bacteria and are responsible for their resistance to Beta-lactam antibiotics like Penicillins ||-||-||-||-||-||-||}A beta-lactam ring ( β -lactam or penam is a Lactam with a Heteroatomic Ring structure, consisting of three Another example are enzymes in the liver called cytochrome P450 oxidases, which are important in drug metabolism. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Cytochrome P450 (abbreviated CYP, P450, infrequently CYP450) is a very large and diverse superfamily of Hemoproteins found in all Domains Drug metabolism is the Metabolism of drugs, their Biochemical modification or degradation usually through specialized enzymatic systems Induction or inhibition of these enzymes can cause drug interactions. A drug interaction is a situation in which a substance affects the activity of a drug, i
2. Enzymes can be compartmentalized, with different metabolic pathways occurring in different cellular compartments. Cellular compartments in Cell biology comprise all closed parts within a cell whose lumen is usually surrounded by a single or double lipid layer For example, fatty acids are synthesized by one set of enzymes in the cytosol, endoplasmic reticulum and the Golgi apparatus and used by a different set of enzymes as a source of energy in the mitochondrion, through β-oxidation. In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle The Golgi apparatus (also called the In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Beta oxidation is the process by which Fatty acids in the form of Acyl-CoA molecules are broken down in Mitochondria and/or in Peroxisomes to ^[67]
3. Enzymes can be regulated by inhibitors and activators. Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. For example, the end product(s) of a metabolic pathway are often inhibitors for one of the first enzymes of the pathway (usually the first irreversible step, called committed step), thus regulating the amount of end product made by the pathways. Such a regulatory mechanism is called a negative feedback mechanism, because the amount of the end product produced is regulated by its own concentration. Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps allocate materials and energy economically, and prevents the manufacture of excess end products. Like other homeostatic devices, the control of enzymatic action helps to maintain a stable internal environment in living organisms. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit
4. Enzymes can be regulated through post-translational modification. Posttranslational modification (PTM is the chemical modification of a Protein after its translation. This can include phosphorylation, myristoylation and glycosylation. Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule Myristic acid, also called tetradecanoic acid, is a common saturated Fatty acid with the molecular formula CH3(CH212COOH Glycosylation is the enzymatic process that links Saccharides to produce glycans, either free or attached to Proteins and Lipids This enzymatic For example, in the response to insulin, the phosphorylation of multiple enzymes, including glycogen synthase, helps control the synthesis or degradation of glycogen and allows the cell to respond to changes in blood sugar. Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule Glycogen synthase ( UDP-glucose-glycogen glucosyltransferase') is a Glycosyltransferase Enzyme ( EC number 2 Glycogen is a Polysaccharide of Glucose (Glc which functions as the secondary short term energy storage in Animal cells Blood sugar, used in a physiological context is a misnomer and misleading ^[68] Another example of post-translational modification is the cleavage of the polypeptide chain. Chymotrypsin, a digestive protease, is produced in inactive form as chymotrypsinogen in the pancreas and transported in this form to the stomach where it is activated. Chymotrypsin (bovine γ chymotrypsin,) is a digestive enzyme that can perform Proteolysis. A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link Chymotrypsinogen is a precursor of the Digestive enzyme Chymotrypsin ( Zymogen) The pancreas is a Gland organ in the digestive and Endocrine system of Vertebrates. In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following This stops the enzyme from digesting the pancreas or other tissues before it enters the gut. This type of inactive precursor to an enzyme is known as a zymogen. A zymogen (or proenzyme) is an inactive Enzyme precursor. A zymogen requires a biochemical change (such as a Hydrolysis reaction revealing the
5. Some enzymes may become activated when localized to a different environment (eg. from a reducing (cytoplasm) to an oxidising (periplasm) environment, high pH to low pH etc). The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. The periplasmic space or periplasm is a space between the inner Cytoplasmic membrane and external Outer membrane of Gram-negative bacteria For example, hemagglutinin in the influenza virus is activated by a conformational change caused by the acidic conditions, these occur when it is taken up inside its host cell and enters the lysosome. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. ^[69]

Involvement in disease

Phenylalanine hydroxylase. Phenylalanine hydroxylase ( is an Enzyme which catalyses the reaction causing the addition of an Hydroxyl group to the end of the 6-carbon aromatic ring of Created from PDB 1KW0

Since the tight control of enzyme activity is essential for homeostasis, any malfunction (mutation, overproduction, underproduction or deletion) of a single critical enzyme can lead to a genetic disease. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit A genetic disorder is a condition caused by abnormalities in Genes or Chromosomes While some diseases such as Cancer, are due to genetic abnormalities acquired The importance of enzymes is shown by the fact that a lethal illness can be caused by the malfunction of just one type of enzyme out of the thousands of types present in our bodies.

One example is the most common type of phenylketonuria. Phenylketonuria ( PKU) is an Autosomal recessive Genetic disorder characterized by a deficiency in the enzyme Phenylalanine hydroxylase A mutation of a single amino acid in the enzyme phenylalanine hydroxylase, which catalyzes the first step in the degradation of phenylalanine, results in build-up of phenylalanine and related products. Phenylalanine hydroxylase ( is an Enzyme which catalyses the reaction causing the addition of an Hydroxyl group to the end of the 6-carbon aromatic ring of Phe redirects here For the BitTorrent feature see PHE. For the constellation see Phoenix (constellation. This can lead to mental retardation if the disease is untreated. Mental retardation is a generalized triarchic disorder characterized by subaverage cognitive functioning and deficits in two or more adaptive behaviors with onset before the age ^[70]

Another example is when germline mutations in genes coding for DNA repair enzymes cause hereditary cancer syndromes such as xeroderma pigmentosum. A Germline Mutation is any detectable and heritable variation in the lineage of germ cells. DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its Genome. Xeroderma pigmentosum, or XP is an Autosomal recessive Genetic disorder of DNA repair in which the ability to repair damage caused by Ultraviolet Defects in these enzymes cause cancer since the body is less able to repair mutations in the genome. This causes a slow accumulation of mutations and results in the development of many types of cancer in the sufferer.

Naming conventions

An enzyme's name is often derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase. Examples are lactase, alcohol dehydrogenase and DNA polymerase. Lactase (LCT a part of the β-galactosidase family of Enzymes is a Glycoside hydrolase involved in the Hydrolysis Alcohol dehydrogenase (ADH is an enzyme discovered in the mid-1960s in Drosophila melanogaster. A DNA Polymerase is an Enzyme that assists in DNA replication. This may result in different enzymes, called isoenzymes, with the same function having the same basic name. Isoenzymes have a different amino acid sequence and might be distinguished by their optimal pH, kinetic properties or immunologically. pH is the measure of the acidity or alkalinity of a Solution. Furthermore, the normal physiological reaction an enzyme catalyzes may not be the same as under artificial conditions. This can result in the same enzyme being identified with two different names. E. g. Glucose isomerase, used industrially to convert glucose into the sweetener fructose, is a xylose isomerase in vivo. Glucose-6-phosphate isomerase, or phosphoglucose isomerase, is an Enzyme ( that catalyzes the conversion of Glucose-6-phosphate into Fructose-6-phosphate Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Fructose (also levulose or laevulose) is a simple reducing Sugar ( Monosaccharide) found in many foods and is one of the three

The International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers; each enzyme is described by a sequence of four numbers preceded by "EC". The International Union of Biochemistry and Molecular Biology ( IUBMB) is an international Non-governmental organisation concerned with Biochemistry and This article is about the Enzyme Commission codes For the European Commission system for coding chemicals see EC-No. The first number broadly classifies the enzyme based on its mechanism:

The top-level classification is

• EC 1 Oxidoreductases: catalyze oxidation/reduction reactions
• EC 2 Transferases: transfer a functional group (e. In Biochemistry, an oxidoreductase is an Enzyme that catalyzes the transfer of Electrons from one molecule (the reductant, also called the hydrogen Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state In Biochemistry, a transferase is an Enzyme that catalyzes the transfer of a Functional group (e In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions g. a methyl or phosphate group)
• EC 3 Hydrolases: catalyze the hydrolysis of various bonds
• EC 4 Lyases: cleave various bonds by means other than hydrolysis and oxidation
• EC 5 Isomerases: catalyze isomerization changes within a single molecule
• EC 6 Ligases: join two molecules with covalent bonds

The complete nomenclature can be browsed at http://www.chem.qmul.ac.uk/iubmb/enzyme/. In Biochemistry, a hydrolase is an Enzyme that catalyzes the Hydrolysis of a Chemical bond. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions In Biochemistry, a lyase is an Enzyme that catalyzes the breaking of various Chemical bonds by means other than Hydrolysis and Oxidation In Biochemistry, an isomerase is an Enzyme that catalyses the structural rearrangement of Isomers Isomerases thus catalyze reactions of the form This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. In Biochemistry, a ligase (from the Latin verb ligāre &mdash "to bind" or "to glue together" is an Enzyme that can catalyse

Industrial applications

Enzymes are used in the chemical industry and other industrial applications when extremely specific catalysts are required. The chemical industry comprises the companies that produce industrial chemicals However, enzymes in general are limited in the number of reactions they have evolved to catalyze and also by their lack of stability in organic solvents and at high temperatures. A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. Consequently, protein engineering is an active area of research and involves attempts to create new enzymes with novel properties, either through rational design or in vitro evolution. Protein engineering is the application of Science, Mathematics, and Economics to the process of developing useful or valuable Proteins It is ^[71][72]

Application	Enzymes used	Uses
Baking industry alpha-amylase catalyzes the release of sugar monomers from starch	Fungal alpha-amylase enzymes are normally inactivated at about 50 degrees Celsius, but are destroyed during the baking process. Baking is the technique of prolonged Cooking of Food by dry heat acting by conduction, and not by radiation, normally in an Oven, A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ	Catalyze breakdown of starch in the flour to sugar. Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Flour is a powder made of Cereal grains It is the key ingredient of Bread, which is a staple food in many countries and therefore the availability Yeast action on sugar produces carbon dioxide. Used in production of white bread, buns, and rolls.
	Proteases	Biscuit manufacturers use them to lower the protein level of flour.
Baby foods	Trypsin	To predigest baby foods. Baby food is any Food, other than breastmilk or infant formula that is given specifically to Infants roughly between the ages of four months Trypsin ( is a Serine protease found in the Digestive system, where it breaks down Proteins Trypsin predominantly cleaves peptide chains at the carboxyl
Brewing industry Germinating barley used for malt. Brewing is the production of Alcoholic beverage and Alcohol fuel through fermentation. Barley ( Hordeum vulgare) is an annual Cereal Grain, which serves as a major animal Feed crop, with smaller amounts used for	Enzymes from barley are released during the mashing stage of beer production.	They degrade starch and proteins to produce simple sugar, amino acids and peptides that are used by yeast for fermentation.
	Industrially produced barley enzymes	Widely used in the brewing process to substitute for the natural enzymes found in barley.
	Amylase, glucanases, proteases	Split polysaccharides and proteins in the malt. Malting is a process applied to Cereal grains in which the grains are made to Germinate by soaking in water and are then quickly halted from germinating further
	Betaglucanases and arabinoxylanases	Improve the wort and beer filtration characteristics.
	Amyloglucosidase and pullulanases	Low-calorie beer and adjustment of fermentability. Beer is the world's oldest and most widely consumed Alcoholic beverage and the third most popular drink overall after water and tea
	Proteases	Remove cloudiness produced during storage of beers.
	Acetolactatedecarboxylase (ALDC)	Avoid the formation of diacetyl
Fruit juices	Cellulases, pectinases	Clarify fruit juices
Dairy industry Roquefort cheese	Rennin, derived from the stomachs of young ruminant animals (like calves and lambs). JUICE is a widely used non-commercial Software package for editing and analysing phytosociological data A dairy is a facility for the extraction and processing of animal Milk &mdashmostly from goats or cows, but also from buffalo, Sheep Chymosin (or rennin) is an aspartic acid protease Enzyme found in Rennet. Physiologically a ruminant is a Mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first stomach known	Manufacture of cheese, used to hydrolyze protein. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions
	Microbially produced enzyme	Now finding increasing use in the dairy industry.
	Lipases	Is implemented during the production of Roquefort cheese to enhance the ripening of the blue-mould cheese. A lipase is a Water-soluble Enzyme that Catalyzes the Hydrolysis of Ester bonds in water–insoluble Lipid Roquefort ( AmE, BrE, French; from Occitan ròcafòrt) is a Sheep milk blue Cheese from the south Danish Blue redirects here for Gabriel Axel's film see Danish Blue.
	Lactases	Break down lactose to glucose and galactose. Lactose (also referred to as milk sugar) is a Sugar which is found most notably in Milk. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology.
Meat tenderizers	Papain	To soften meat for cooking. In Cooking, tenderizing is a process to break down Collagens in Meat to make it more palatable for consumption Papain is a Cysteine protease ( Hydrolase Enzyme present in Papaya ( Carica papaya) and Mountain papaya ( Vasconcellea
Starch industry Glucose Fructose	Amylases, amyloglucosideases and glucoamylases	Converts starch into glucose and various syrups. Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Inverted sugar syrup is a Sucrose -based Syrup produced with the Glycoside hydrolase Enzyme Invertase or an Acid, which
	Glucose isomerase	Converts glucose into fructose in production of high fructose syrups from starchy materials. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Fructose (also levulose or laevulose) is a simple reducing Sugar ( Monosaccharide) found in many foods and is one of the three High-fructose corn syrup (HFCS is any of a group of Corn syrups that has undergone Enzymatic processing to increase its Fructose content and is then mixed These syrups have enhanced sweetening properties and lower calorific values than sucrose for the same level of sweetness. This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy.
Paper industry A paper mill in South Carolina. Paper is thin material mainly used for writing upon printing upon or packaging South Carolina ( is a state in the southern region ( Deep South) of the United States of America.	Amylases, Xylanases, Cellulases and ligninases	Degrade starch to lower viscosity, aiding sizing and coating paper. Amylase is an Enzyme that breaks Starch down into Sugar. Amylase is present in human Saliva, where it begins the chemical process Xylanase ( is the name given to a class of Enzymes which degrade the linear Polysaccharide beta-14-xylan into Xylose, thus breaking down Cellulase refers to a class of Enzymes produced chiefly by Fungi, Bacteria, and Protozoans that Catalyze the cellulolysis (or Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. Sizing or size is a Substance that is applied to Porous materials as a Glaze or Filler. Xylanases reduce bleach required for decolorising; cellulases smooth fibers, enhance water drainage, and promote ink removal; lipases reduce pitch and lignin-degrading enzymes remove lignin to soften paper. Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants
Biofuel industry Cellulose in 3D	Cellulases	Used to break down cellulose into sugars that can be fermented (see cellulosic ethanol). Cellulase refers to a class of Enzymes produced chiefly by Fungi, Bacteria, and Protozoans that Catalyze the cellulolysis (or Cellulosic ethanol also know by the name Ceetol, is a Biofuel produced from wood grasses or the non-edible parts of plants
	Ligninases	Use of lignin waste
Biological detergent Laundry soap	Primarily proteases, produced in an extracellular form from bacteria	Used for presoak conditions and direct liquid applications helping with removal of protein stains from clothes. Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants A biological detergent is a Laundry detergent that contains Enzymes. A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link In Cell biology, Molecular biology and related fields the word extracellular (or sometimes extracellular space) means "outside the cell The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have
	Amylases	Detergents for machine dish washing to remove resistant starch residues. Amylase is an Enzyme that breaks Starch down into Sugar. Amylase is present in human Saliva, where it begins the chemical process
	Lipases	Used to assist in the removal of fatty and oily stains. A lipase is a Water-soluble Enzyme that Catalyzes the Hydrolysis of Ester bonds in water–insoluble Lipid
	Cellulases	Used in biological fabric conditioners. Cellulase refers to a class of Enzymes produced chiefly by Fungi, Bacteria, and Protozoans that Catalyze the cellulolysis (or Fabric softener (also called Fabric Conditioner) is used to prevent Static cling and make fabric softer
Contact lens cleaners	Proteases	To remove proteins on contact lens to prevent infections. A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the Cornea A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the Cornea
Rubber industry	Catalase	To generate oxygen from peroxide to convert latex into foam rubber. Catalase is a common Enzyme found in nearly all living organisms where it functions to catalyze the decomposition of Hydrogen peroxide to Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the A peroxide is a compound containing an Oxygen -oxygen single bond. LaTeX (ˈleɪtɛ
Photographic industry	Protease (ficin)	Dissolve gelatin off scrap film, allowing recovery of its silver content. Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing Gelatin (also gelatine, from French gélatine) is a translucent colourless brittle nearly tasteless solid substance, extracted from the This article is mainly concerned with Still photography film For Motion picture film please see Film stock. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen
Molecular biology Part of the DNA double helix. Molecular biology is the study of Biology at a molecular level In Geometry a double helix (plural helices) typically consists of two congruent helices with the same axis differing by a translation	Restriction enzymes, DNA ligase and polymerases	Used to manipulate DNA in genetic engineering, important in pharmacology, agriculture and medicine. A restriction enzyme (or restriction Endonuclease) is an Enzyme that cuts double-stranded DNA at specific recognition Nucleotide In Molecular biology, DNA ligase is a special type of Ligase ( that can link together two DNA strands that have single-strand breaks (a break in both complementary A polymerase (EC 2776/7/19/48/49 is an Enzyme whose central function is associated with Polymers of Nucleic acids such as RNA and DNA Genetic engineering, Recombinant DNA technology, genetic modification/manipulation (GM and gene splicing are terms that apply to the direct Pharmacology (from Greek grc φάρμακον pharmakon, "drug" and grc -λογία -logia) is the study of how Drugs Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the Essential for restriction digestion and the polymerase chain reaction. A restriction enzyme (or restriction Endonuclease) is an Enzyme that cuts double-stranded DNA at specific recognition Nucleotide Molecular biology is also important in forensic science.

See also

• List of enzymes
• Enzyme assay
• Enzyme catalysis
• RNA Biocatalysis
• SUMO enzymes
• K_i Database
• Proteonomics and protein engineering
• Immobilized enzyme

References

Further reading

External links

• Structure/Function of Enzymes, Web tutorial on enzyme structure and function.
• Enzymes in diagnosis,Role of enzymes in diagnosis of diseases.
• Enzyme spotlight Monthly feature at the European Bioinformatics Institute on a selected enzyme.
• AMFEP, Association of Manufacturers and Formulators of Enzyme Products
• BRENDA database, a comprehensive compilation of information and literature references about all known enzymes; requires payment by commercial users.
• Enzyme Structures Database links to the known 3-D structure data of enzymes in the Protein Data Bank. The Protein Data Bank ( PDB) is a repository for 3-D structural data of Proteins and Nucleic acids These data typically obtained by X-ray crystallography
• ExPASy enzyme database, links to Swiss-Prot sequence data, entries in other databases and to related literature searches. Swiss-Prot is a manually curated Biological database of Protein sequences
• KEGG: Kyoto Encyclopedia of Genes and Genomes Graphical and hypertext-based information on biochemical pathways and enzymes.
• MACiE database of enzyme reaction mechanisms.
• MetaCyc database of enzymes and metabolic pathways
• 'Face-to-Face Interview with Sir John Cornforth who was awarded a Nobel Prize for work on stereochemistry of enzyme-catalyzed reactions Freeview video by the Vega Science Trust
• Sigma Aldrich Enzyme Assays by Enzyme Name - 100's of assays sorted by enzyme name. The MetaCyc database contains extensive information on Metabolic pathways and Enzymes from many organisms