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Human lysozyme. The reaction product N-acetyllactosamine shown as a space-filling model occupies the active site.

Enzymes /ˈɛnzaɪmz/ are molecules that accelerate, or catalyze, chemical reactions. In these reactions, the molecules at the beginning of the process are called substrates and the enzyme converts these into different molecules, called products. Almost all metabolic processes in the cell need enzymes in order to occur at rates fast enough to sustain life. The set of enzymes made in a cell determines which metabolic pathways occur in that cell. The study of enzymes is called enzymology.

Enzymes are known to catalyze about 5,400 biochemical reactions.^[1] Most enzymes are proteins, although a few are catalytic RNA molecules, such as the ribosome. All enzymes get their extraordinary specificity from their unique three-dimensional structure.

Like all catalysts, enzymes increase the rate of a reaction by lowering its activation energy. Some enzymes can make their conversion of substrate to product occur many millions of times faster. 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. When decarboxylase is added, the same process takes just 25 milliseconds.^[2] Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity, and activators are molecules that increase activity. Drugs and poisons are often enzyme inhibitors. Enzymes are also affected by features of their environment, such as temperature, pressure, and pH.

Some enzymes are used commercially, for example, in the synthesis of antibiotics. Some household products use enzymes to speed up chemical reactions: enzymes in biological washing powders break down protein or fat stains on clothes, and enzymes in meat tenderizer break down proteins into smaller molecules, making the meat easier to chew.

Etymology and history

By the late 17th and early 18th centuries, the digestion of meat by stomach secretions^[3] and the conversion of starch to sugars by plant extracts and saliva were known but the mechanisms by which these occurred had not been identified.^[4]

French chemist Anselme Payen discovered the first enzyme, diastase, in 1833.^[5] A few decades later, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that this fermentation was caused by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms. 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."^[6]

In 1877, German physiologist Wilhelm Kühne (1837–1900) first used the term enzyme, which comes from Greek ἔνζυμον, "leavened", to describe this process.^[7] The word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment was used to refer to chemical activity produced by living organisms.

Eduard Buchner submitted his first paper on the study of yeast extracts in 1897. In a series of experiments at the University of Berlin, he found that sugar was fermented by yeast extracts even when there were no living yeast cells in the mixture.^[8] He named the enzyme that brought about the fermentation of sucrose "zymase".^[9] In 1907, he received the Nobel Prize in Chemistry for "his discovery of cell-free fermentation". Following Buchner's example, enzymes are usually named according to the reaction they carry out: the suffix -ase is added to the name of the substrate (e.g., lactase is the enzyme that cleaves lactose) or to the type of reaction (e.g., DNA polymerase forms DNA polymers).^[10]

The biochemical nature of enzymes was at this point still unknown. Many scientists observed that enzymatic activity was associated with proteins, but others (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.^[11] In 1926, James B. Sumner showed that the enzyme urease was a pure protein and crystallized it; he did likewise for the enzyme catalase in 1937. The conclusion that pure proteins can be enzymes was definitively demonstrated by John Howard Northrop and Wendell Meredith Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. These three scientists were awarded the 1946 Nobel Prize in Chemistry.^[12]

The discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. 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.^[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.

Structure

Enzymes are in general 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.^[15] A small number of RNA-based biological catalysts exist, with the most common being the ribosome; these are referred to as either RNA-enzymes or ribozymes. The activities of enzymes are determined by their three-dimensional structure.^[16] Although structure does determine function, predicting a novel enzyme's activity from its structure is a problem that has not yet been solved.^[17]

Most enzymes are much larger than the substrates they act on, and only a small portion of the enzyme (around 2–4 amino acids) is directly involved in catalysis.^[18] The region that contains these catalytic residues, binds the substrate, and then carries out the reaction is known as the active site. Enzymes can also contain sites that bind cofactors, which are needed 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.

Like all proteins, enzymes are long, linear chains of amino acids that fold to produce a three-dimensional product. 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. Most enzymes can be denatured – that is, unfolded and inactivated – by heating or chemical denaturants, which disrupt the three-dimensional structure of the protein. 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. Enzymes can also show impressive levels of stereospecificity, regioselectivity and chemoselectivity.^[19]

Some of the enzymes showing the highest specificity and accuracy are involved in the copying and expression of the genome. 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.^[20] This two-step process results in average error rates of less than 1 error in 100 million reactions in high-fidelity mammalian polymerases.^[21] Similar proofreading mechanisms are also found in RNA polymerase,^[22] aminoacyl tRNA synthetases^[23] and ribosomes.^[24]

Whereas some enzymes have broad-specificity, as they can act on a relatively broad range of different physiologically relevant substrates, many enzymes possess small side activities which arose fortuitously (i.e. neutrally), which may be the starting point for the evolutionary selection of a new function; this phenomenon is known as enzyme promiscuity.^[25]

Mechanism

"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.^[26] This is often referred to as "the lock and key" model. This model explains enzyme specificity, but fails to explain the stabilization of the transition state that enzymes achieve.

Induced fit model

In 1958, Daniel Koshland suggested a modification to the lock and key model: since enzymes are rather flexible structures, the active site is continuously reshaped by interactions with the substrate as the substrate interacts with the enzyme.^[27] As a result, the substrate does not simply bind to a rigid active site; the amino acid side-chains that make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function. In some cases, such as glycosidases, the substrate molecule also changes shape slightly as it enters the active site.^[28] The active site continues to change until the substrate is completely bound, at which point the final shape and charge is determined.^[29] Induced fit may enhance the fidelity of molecular recognition in the presence of competition and noise via the conformational proofreading mechanism.^[30]

Reducing activation energy

Enzymes can act in several ways, all of which lower the activation energy (ΔG^‡, Gibbs free energy):^[31]

By stabilizing the transition state; for example:
1. Distorting the bound substrate(s) into their transition state form, thereby reducing the amount of energy required to complete the reaction.
2. Creating an environment with a charge distribution complementary to that of the transition state.^[32]
By 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.
By reducing the reaction entropy change through productive orientation of substrate molecules. This entropic effect involves destabilization of the ground state,^[33] and its contribution to catalysis is relatively small.^[34]

Dynamics

The internal dynamics of enzymes are important for their catalytic function.^[35] Internal dynamics are the movement of parts of the enzyme's structure, such as individual amino acid residues, a group of amino acids, or even an entire protein domain. These movements occur at various time-scales ranging from femtoseconds to seconds and can be studied using biophysical techniques such as nuclear magnetic resonance spectroscopy^[36] or time resolved crystallography.^[37] Networks of protein residues throughout an enzyme's structure can contribute to its function through collective dynamic motions.^[38] This behavior can be modeled by extension of the Michaelis-Menten kinetic model to multiple reaction pathways.^[39] Protein dynamics are important for binding and releasing substrates and products, and for interacting with other proteins involved in regulating an enzyme's activity, but the role of dynamics in catalysis itself is controversial.^[40]

Allosteric modulation

Allosteric sites are sites on the enzyme that bind to molecules in the cellular environment. The sites form weak, noncovalent bonds with these molecules, causing a change in the conformation of the enzyme. This change in conformation translates to the active site, which then affects the reaction rate of the enzyme.^[41] Allosteric interactions can both inhibit and activate enzymes and are a common way that enzymes are controlled in the body.^[42]

Cofactors

Some enzymes do not need any additional components to show full activity. Others require non-protein molecules called cofactors to be bound for activity.^[43] Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds (e.g., flavin and heme). 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. Coenzymes include NADH, NADPH and adenosine triphosphate. These molecules transfer chemical groups between enzymes.^[44]

An example of an enzyme that contains a cofactor is carbonic anhydrase, which is shown in the ribbon diagram above with a zinc cofactor bound as part of its active site.^[45] 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.

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 (or haloenzyme) (this is the active form). Most cofactors are not covalently attached to an enzyme, but are very tightly bound. Organic prosthetic groups can be covalently bound (e.g., biotin in enzymes such as pyruvate carboxylase).^[46] The term holoenzym can also be applied to enzymes that contain multiple protein subunits, such as the DNA polymerases; here the holoenzyme is the complete complex containing all the subunits needed for activity.

Coenzymes

Space-filling model of the coenzyme NADH

Coenzymes are small organic molecules that can be loosely or tightly bound to an enzyme. Tightly bound coenzymes can be called prosthetic groups. Coenzymes transport chemical groups from one enzyme to another.^[47] Some of these chemicals such as riboflavin, thiamine and folic acid are vitamins (compounds that cannot be synthesized by the body and must be acquired from the diet). The chemical groups carried include the hydride ion (H⁻) carried by NAD or NADP⁺, the phosphate group carried by adenosine triphosphate, the acetyl group carried by coenzyme A, formyl, methenyl or methyl groups carried by folic acid and the methyl group carried by S-adenosylmethionine.

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 1000 enzymes are known to use the coenzyme NADH.^[48]

Coenzymes are usually continuously 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. This continuous regeneration means that even small amounts of coenzymes are used very intensively. For example, the human body turns over its own weight in ATP each day.^[49]

Thermodynamics

As all catalysts, enzymes do not alter the position of the chemical equilibrium of the reaction. Usually, in the presence of an enzyme, the reaction runs in the same direction as it would without the enzyme, just more quickly. In the absence of the enzyme, other uncatalyzed, spontaneous reactions might lead to different products, because in those conditions this different product is formed faster.

For example, carbonic anhydrase catalyzes its reaction in either direction depending on the concentration of its reactants.

\mathrm {CO_{2}+H_{2}O{\xrightarrow {Carbonic\ anhydrase}}H_{2}CO_{3}}

(in tissues; high CO₂ concentration)

\mathrm {H_{2}CO_{3}{\xrightarrow {Carbonic\ anhydrase}}CO_{2}+H_{2}O}

(in lungs; low CO₂ concentration)

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.^[50]

Kinetics

Enzyme kinetics is the investigation of how enzymes bind substrates and turn them into products. The rate data used in kinetic analyses are commonly obtained from enzyme assays. In 1913 Leonor Michaelis and Maud Leonora Menten proposed a quantitative theory of enzyme kinetics, which is referred to as Michaelis-Menten kinetics.^[51] The major contribution of Michaelis and Menten 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-Menten complex in their honor. The enzyme then catalyzes the chemical step in the reaction and releases the product. This work was further developed by G. E. Briggs and J. B. S. Haldane, who derived kinetic equations that are still widely used today.^[52]

Enzyme rates depend on solution conditions and substrate concentration. 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 complex. At the maximum reaction rate (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.

V_max is only one of several important kinetic parameters. 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 reaction rate; generally, each enzyme has a characteristic K_m for a given substrate. Another useful constant is k_cat, also called the turnover number, which is the number of substrate molecules handled by one active site per second.^[53]

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 up to and including the first irreversible step. 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. Example of such enzymes are triose-phosphate isomerase, carbonic anhydrase, acetylcholinesterase, catalase, fumarase, β-lactamase, and superoxide dismutase.^[54]^[55] The turnover of such enzymes can reach several million reactions per second.

Michaelis-Menten kinetics relies on the law of mass action, which is derived from the assumptions of free diffusion and thermodynamically driven random collision. Many biochemical or cellular processes deviate significantly from these conditions, because of macromolecular crowding and constrained molecular movement.^[56] More recent, complex extensions of the model attempt to correct for these effects.^[57]

Inhibition

Enzyme reaction rates can be decreased by various types of enzyme inhibitors.^[58]^: 73–74

Types of inhibition

Competitive: The inhibitor and substrate cannot bind to the enzyme at the same time.^[59] 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. The similarity between the structures of folic acid and this drug are shown in the figure to the right. In some cases, the inhibitor can bind to a site other than the binding-site of the usual substrate and exert an allosteric effect to change the shape of the usual binding-site.
Uncompetitive: The inhibitor cannot bind to the free enzyme, only to the enzyme-substrate complex. In the presence of the inhibitor, the enzyme-substrate complex is inactive.^[58]^: 78 This type of inhibition is rare.^[60]
Non-competitive: The inhibitor can bind to the enzyme at the same time as the substrate, but not to the active site. In the presence of the inhibitor, the enzyme can bind the substrate but not catalyze the reaction. 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.^[58]^: 76–78
Mixed: Binding of the substrate and the inhibitor affect each other. The enzyme's function is reduced but not eliminated when bound to the inhibitor. This type of inhibitor does not follow the Michaelis-Menten equation.^[58]^: 76–78
Irreversible: The inhibitor permanently inactivates the enzyme, usually by forming a covalent bond to the protein. Penicillin^[61] and aspirin^[62] are common drugs that act in this manner.

Functions of inhibitors

In many organisms, inhibitors may act as part of a feedback mechanism. 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.

Since inhibitors modulate the function of enzymes they are often used as drugs. Many such drugs are reversible competitive inhibitors that resemble the enzyme's native substrate, similar to methotrexate above; other well-known examples include statins used to treat high cholesterol,^[63] and protease inhibitors used to treat retroviral infections such as HIV.^[64] A common example of an irreversible inhibitor that is 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. Other enzyme inhibitors are poisons. For example, the poison cyanide is an irreversible enzyme inhibitor that combines with the copper and iron in the active site of the enzyme cytochrome c oxidase and blocks cellular respiration.^[65]

Biological function

Enzymes serve a wide variety of functions inside living organisms. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases.^[66] They also generate movement, with myosin hydrolyzing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton.^[67] Other ATPases in the cell membrane are ion pumps involved in active transport. Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies.^[68] 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.

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. Starch molecules, for example, are too large to be absorbed from the intestine, but enzymes hydrolyze the starch chains into smaller molecules such as maltose and eventually glucose, which can then be absorbed. Different enzymes digest different food substances. In ruminants, which have herbivorous diets, microorganisms in the gut produce another enzyme, cellulase, to break down the cellulose cell walls of plant fiber.^[69]

Metabolism

Glycolytic enzymes and their functions in the metabolic pathway of glycolysis

Several enzymes can work together in a specific order, creating metabolic pathways.^[70] 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 provided by one enzyme but an inducible high activity from a second enzyme.^[71]

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. Glucose, for example, can react directly with ATP to become phosphorylated at one or more of its carbons. In the absence of enzymes, this occurs so slowly as to be insignificant. 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. As a consequence, the network of metabolic pathways within each cell depends on the set of functional enzymes that are present.^[70]

Control of activity

There are four main ways that enzyme activity is controlled in the cell.^[72]

Quantity: 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. This form of gene regulation is called enzyme induction. 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.^[73] Another example are enzymes in the liver called cytochrome P450 oxidases, which are important in drug metabolism. Induction or inhibition of these enzymes can cause drug interactions.^[74] Enzyme levels can also be regulated by changing the rate of enzyme degradation.
Subcellular distribution: Enzymes can be compartmentalized, with different metabolic pathways occurring in different cellular compartments. For example, fatty acids are synthesized by one set of enzymes in the cytosol, endoplasmic reticulum and golgi and used by a different set of enzymes as a source of energy in the mitochondrion, through β-oxidation.^[75] In addition, trafficking of the enzyme to different compartments may change the degree of protonation (cytoplasm neutral and lysosome acidic) or oxidative state [e.g., oxidized (periplasm) or reduced (cytoplasm)] which in turn affects enzyme activity.^[76]
Activation or inhibition: 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.^[77]^: 141–48 Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps with effective allocations of materials and energy economy, and it prevents the excess manufacture of end products. Like other homeostatic devices, the control of enzymatic action helps to maintain a stable internal environment in living organisms.
Post-translational modification: These can include phosphorylation, myristoylation and glycosylation.^[77]^: 149–69 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.^[78] 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. 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.^[77]^: 149–53

Involvement in disease

Phenylalanine hydroxylase, 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. 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 of enzyme deficiency is the most common type of phenylketonuria. 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. This can lead to intellectual disability if the disease is untreated.^[79] Another example is pseudocholinesterase deficiency, in which the body's ability to break down choline ester drugs is impaired.^[80] Oral administration of enzymes can be used to treat some functional enzyme deficiencies, such as pancreatic insufficiency and lactose intolerance.

Another way enzyme malfunctions can cause disease comes from germline mutations in genes coding for DNA repair enzymes. These mutations can cause hereditary cancer syndromes such as xeroderma pigmentosum. 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 cancers.

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. Different enzymes that catalyze the same chemical reaction are called isozymes.

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 first number broadly classifies the enzyme based on its mechanism.

The top-level classification is^[81]

EC 1, Oxidoreductases: catalyze oxidation/reduction reactions
EC 2, Transferases: transfer a functional group (e.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.

Industrial applications

Enzymes are used in the chemical industry and other industrial applications when extremely specific catalysts are required. 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. As a consequence, 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.^[82]^[83] These efforts have begun to be successful, and a few enzymes have now been designed "from scratch" to catalyze reactions that do not occur in nature.^[84]

Application	Enzymes used	Uses
Food processing	Amylases from fungi and plants	Produce sugars from starch, such as in making high-fructose corn syrup.^[85]
Food processing	Proteases	Lower the protein level of flour, as in biscuit-making.
Baby foods	Trypsin	Digest baby foods
Brewing industry	Enzymes from barley are released during the mashing stage of beer production.	Degrade starch and proteins to produce simple sugar, amino acids and peptides that are used by yeast for fermentation.
	Industrially produced barley enzymes	Substitute for the natural enzymes found in barley.
	Amylase, glucanases, proteases	Split polysaccharides and proteins in the malt.
	Betaglucanases and arabinoxylanases	Improve the wort and beer filtration characteristics.
	Amyloglucosidase and pullulanases	Make low-calorie beer and adjust fermentability.
	Proteases	Remove cloudiness produced during storage of beers.
	Acetolactate decarboxylase (ALDC)	Increase fermentation efficiency by reducing diacetyl formation.^[86]
Fruit juices	Cellulases, pectinases	Clarify fruit juices.
Dairy industry	Rennin, originally derived from the stomachs of young: ruminant animals (like calves and lambs), but now often from genetically-modified bacteria^[87]^[88]	Hydrolyze protein in the manufacture of cheese
	Lipases	Produce Roquefort cheese and enhance the ripening of blue-mold cheese.
	Lactases	Break down lactose to glucose and galactose.
Meat tenderizers	Papain	Soften meat for cooking
Starch industry	Amylases, amyloglucosideases and glucoamylases	Convert starch into glucose and various syrups.
Starch industry	Glucose isomerase	Convert glucose into fructose in production of high-fructose syrups from starchy materials.
Paper industry	Amylases, xylanases, cellulases and ligninases	Degrade starch to lower viscosity, aiding sizing and coating paper.
Biofuel industry	Cellulases	Break down cellulose into sugars that can be fermented to produce cellulosic ethanol
Biofuel industry	Ligninases	Use of lignin waste
Biological detergent	Primarily proteases, produced in an extracellular form from bacteria	Remove protein stains from clothes and fabric
	Amylases	Detergents for machine dish washing to remove resistant starch residues
	Lipases	Remove fatty and oily stains from clothes and fabric
	Cellulases	Improve performance of laundry detergent
Contact lens cleaners	Proteases	Remove proteins on contact lenses to prevent infections
Rubber industry	Catalase	Generate oxygen from peroxide to convert latex into foam rubber
Photographic industry	Protease (ficin)	Dissolve gelatin off scrap film, allowing recovery of its silver content.
Molecular biology	Restriction enzymes, DNA ligase and polymerases	Manipulate DNA in genetic engineering, such as in restriction digestion and the polymerase chain reaction.

References

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^ Radzicka A, Wolfenden R (January 1995). "A proficient enzyme". Science. 267 (5194): 90–931. PMID 7809611.
^ de Réaumur RA (1752). "Observations sur la digestion des oiseaux". Histoire de l'academie royale des sciences. 1752: 266, 461.
^ Williams, Henry Smith (1904). A History of Science: in Five Volumes. Volume IV: Modern Development of the Chemical and Biological Sciences. Harper and Brothers. {{cite book}}: Unknown parameter |name-list-format= ignored (|name-list-style= suggested) (help)
^ Payen A, Persoz JF (1833). "Mémoire sur la diastase, les principaux produits de ses réactions et leurs applications aux arts industriels" [Memoir on diastase, the principal products of its reactions, and their applications to the industrial arts]. Annales de chimie et de physique. 2nd (in French). 53: 73–92.
^ Manchester KL (December 1995). "Louis Pasteur (1822-1895)–chance and the prepared mind". Trends in Biotechnology. 13 (12): 511–5. doi:10.1016/S0167-7799(00)89014-9. PMID 8595136.
^ Kühne coined the word "enzyme" in: Kühne W (1877). "Über das Verhalten verschiedener organisirter und sog. ungeformter Fermente" [On the behavior of various organized and so-called unformed ferments]. Verhandlungen des naturhistorisch-medicinischen Vereins zu Heidelberg. new series (in German). 1 (3): 190–193. The relevant passage occurs on page 190: "Um Missverständnissen vorzubeugen und lästige Umschreibungen zu vermeiden schlägt Vortragender vor, die ungeformten oder nicht organisirten Fermente, deren Wirkung ohne Anwesenheit von Organismen und ausserhalb derselben erfolgen kann, als Enzyme zu bezeichnen." (Translation: In order to obviate misunderstandings and avoid cumbersome periphrases, [the author, a university lecturer] suggests designating as "enzymes" the unformed or not organized ferments, whose action can occur without the presence of organisms and outside of the same.)
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^ Wagner AL (1975). Vitamins and Coenzymes. Krieger Pub Co. ISBN 0-88275-258-8.
^ "BRENDA The Comprehensive Enzyme Information System". Technische Universität Braunschweig. Retrieved 23 February 2015.
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^ Voet D, Voet G (2011). Biochemistry (4th ed.). Hoboken, NJ: John Wiley & Sons. p. 490. ISBN 978-0-470-57095-1.
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^ Ellis RJ (October 2001). "Macromolecular crowding: obvious but underappreciated". Trends in Biochemical Sciences. 26 (10): 597–604. doi:10.1016/S0968-0004(01)01938-7. PMID 11590012.
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^ ^a ^b ^c ^d Cornish-Bowden A (2004). Fundamentals of enzyme kinetics (3 ed.). London: Portland Press. ISBN 1-85578-158-1.
^ Price NC (1979). "What is meant by 'competitive inhibition'?". Trends in Biochemical Sciences. 4 (11): pN272. doi:10.1016/0968-0004(79)90205-6.
^ Cornish-Bowden A (July 1986). "Why is uncompetitive inhibition so rare? A possible explanation, with implications for the design of drugs and pesticides". FEBS Letters. 203 (1): 3–6. PMID 3720956.
^ Fisher JF, Meroueh SO, Mobashery S (February 2005). "Bacterial resistance to beta-lactam antibiotics: compelling opportunism, compelling opportunity". Chemical Reviews. 105 (2): 395–424. doi:10.1021/cr030102i. PMID 15700950.
^ Sharma S, Sharma SC (October 1997). "An update on eicosanoids and inhibitors of cyclooxygenase enzyme systems". Indian Journal of Experimental Biology. 35 (10): 1025–31. PMID 9475035.
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^ Yoshikawa S, Caughey WS (May 1990). "Infrared evidence of cyanide binding to iron and copper sites in bovine heart cytochrome c oxidase. Implications regarding oxygen reduction". The Journal of Biological Chemistry. 265 (14): 7945–58. PMID 2159465.
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^ Berg JS, Powell BC, Cheney RE (April 2001). "A millennial myosin census". Molecular Biology of the Cell. 12 (4): 780–94. doi:10.1091/mbc.12.4.780. PMC 32266. PMID 11294886.
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^ Mackie RI, White BA (October 1990). "Recent advances in rumen microbial ecology and metabolism: potential impact on nutrient output". Journal of Dairy Science. 73 (10): 2971–95. doi:10.3168/jds.S0022-0302(90)78986-2. PMID 2178174.
^ ^a ^b Blackstock JC (1989). "Chapter 10.5: Metabolic Pathways". Guide to Biochemistry. London: Wright. p. 117. ISBN 0-7236-1151-3. {{cite book}}: External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
^ Rouzer CA, Marnett LJ (2009). "Cyclooxygenases: structural and functional insights". J. Lipid Res. 50 Suppl: S29–34. doi:10.1194/jlr.R800042-JLR200. PMC 2674713. PMID 18952571.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ Price NC, Stevens L (2000). "Chapter 6: The control of enzyme activity". Fundamentals of enzymology : the cell and molecular biology of catalytic proteins (3 ed.). Oxford: Oxford Univ. Press. pp. 217–272. ISBN 0-19-850229-X.
^ Bennett PM, Chopra I (1993). "Molecular basis of beta-lactamase induction in bacteria" (PDF). Antimicrob. Agents Chemother. 37 (2): 153–8. PMC 187630. PMID 8452343.
^ Skett P, Gibson GG (2001). "Chapter 3: Induction and Inhibition of Drug Metabolism". Introduction to drug metabolism (3 ed.). Cheltenham, UK: Nelson Thornes Publishers. pp. 87–118. ISBN 978-0748760114.
^ Faergeman NJ, Knudsen J (April 1997). "Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling". The Biochemical Journal. 323 ( Pt 1) (Pt 1): 1–12. PMC 1218279. PMID 9173866.
^ Suzuki H (2015). "Chapter 4: Effect of pH, Temperature, and High Pressure on Enzymatic Activity". How Enzymes Work: From Structure to Function. Boca Raton, FL: CRC Press. pp. 53–74. ISBN 978-981-4463-92-8.
^ ^a ^b ^c Suzuki H (2015). "Chapter 8: Control of Enzyme Activity". How Enzymes Work: From Structure to Function. Boca Raton, FL: CRC Press. pp. 141–69. ISBN 978-981-4463-92-8.
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^ "Pseudocholinesterase deficiency". U.S. National Library of Medicine. Retrieved 5 September 2013.
^ The complete nomenclature can be browsed at: Moss GP. "Enzyme Nomenclature. Recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology on the Nomenclature and Classification of Enzymes by the Reactions they Catalyse". School of Biological and Chemical Sciences, Queen Mary, University of London. Retrieved 23 February 2015.
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@@ Line 133: / Line 133: @@
 [[Image:Methotrexate vs folate.svg|thumb|thumb|right|The coenzyme folic acid (top) and the anti-cancer drug methotrexate (bottom) are very similar in structure. As a result, methotrexate is a competitive inhibitor of many enzymes that use folates.]]
-*''[[Competitive inhibition|Competitive]]'': the inhibitor and substrate cannot bind to the enzyme at the same time.<ref>{{vcite2 journal | vauthors = Price NC | year = 1979 | title = What is meant by 'competitive inhibition'? | journal = Trends in Biochemical Sciences | volume = 4 | issue=11 | pages = pN272 | doi = 10.1016/0968-0004(79)90205-6 }}</ref> 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 [[folic acid|dihydrofolate]] to [[folic acid|tetrahydrofolate]]. The similarity between the structures of folic acid and this drug are shown in the figure to the right. In some cases, the inhibitor can bind to a site other than the binding-site of the usual substrate and exert an [[#Allosteric modulation|allosteric effect]] to change the shape of the usual binding-site.
+;[[Competitive inhibition|Competitive]]: The inhibitor and substrate cannot bind to the enzyme at the same time.<ref>{{vcite2 journal | vauthors = Price NC | year = 1979 | title = What is meant by 'competitive inhibition'? | journal = Trends in Biochemical Sciences | volume = 4 | issue=11 | pages = pN272 | doi = 10.1016/0968-0004(79)90205-6 }}</ref> 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 [[folic acid|dihydrofolate]] to [[folic acid|tetrahydrofolate]]. The similarity between the structures of folic acid and this drug are shown in the figure to the right. In some cases, the inhibitor can bind to a site other than the binding-site of the usual substrate and exert an [[#Allosteric modulation|allosteric effect]] to change the shape of the usual binding-site.
+;[[Uncompetitive inhibition|Uncompetitive]]: The inhibitor cannot bind to the free enzyme, only to the enzyme-substrate complex. In the presence of the inhibitor, the enzyme-substrate complex is inactive.<ref name = "Cornish-Bowden_2004"/>{{rp|78}} This type of inhibition is rare.<ref>{{vcite2 journal | vauthors = Cornish-Bowden A | title = Why is uncompetitive inhibition so rare? A possible explanation, with implications for the design of drugs and pesticides | journal = FEBS Letters | volume = 203 | issue = 1 | pages = 3-6 | date = Jul 1986 | pmid = 3720956 }}</ref>
-*''[[Uncompetitive inhibition|Uncompetitive]]'': the inhibitor cannot bind to the free enzyme, only to the enzyme-substrate complex. In the presence of the inhibitor, the enzyme-substrate complex is inactive.<ref name = "Cornish-Bowden_2004"/>{{rp|78}} This type of inhibition is rare.<ref>{{vcite2 journal | vauthors = Cornish-Bowden A | title = Why is uncompetitive inhibition so rare? A possible explanation, with implications for the design of drugs and pesticides | journal = FEBS Letters | volume = 203 | issue = 1 | pages = 3-6 | date = Jul 1986 | pmid = 3720956 }}</ref>
+;[[Non-competitive inhibition|Non-competitive]]: The inhibitor can bind to the enzyme at the same time as the substrate, but not to the active site. In the presence of the inhibitor, the enzyme can bind the substrate but not catalyze the reaction. Because the inhibitor can not be driven from the enzyme by higher substrate concentration (in contrast to competitive inhibition), the apparent V<sub>max</sub> changes. But because the substrate can still bind to the enzyme, the K<sub>m</sub> stays the same.<ref name = "Cornish-Bowden_2004"/>{{rp|76–78}}
+;[[Mixed inhibition|Mixed]]: Binding of the substrate and the inhibitor affect each other. The enzyme's function is reduced but not eliminated when bound to the inhibitor. This type of inhibitor does not follow the Michaelis-Menten equation.<ref name = "Cornish-Bowden_2004"/>{{rp|76–78}}
+;[[Irreversible inhibition|Irreversible]]: The inhibitor permanently inactivates the enzyme, usually by forming a [[covalent bond]] to the protein. [[Penicillin]]<ref>{{vcite2 journal | vauthors = Fisher JF, Meroueh SO, Mobashery S | title = Bacterial resistance to beta-lactam antibiotics: compelling opportunism, compelling opportunity | journal = Chemical Reviews | volume = 105 | issue = 2 | pages = 395-424 | date = Feb 2005 | pmid = 15700950 | doi = 10.1021/cr030102i }}</ref> and [[aspirin]]<ref name="pmid9475035">{{vcite2 journal | vauthors = Sharma S, Sharma SC | title = An update on eicosanoids and inhibitors of cyclooxygenase enzyme systems | journal = Indian Journal of Experimental Biology | volume = 35 | issue = 10 | pages = 1025–31 | date = Oct 1997 | pmid = 9475035 | doi =  }}</ref> are common drugs that act in this manner.
-*''[[Non-competitive inhibition|Non-competitive]]'': the inhibitor can bind to the enzyme at the same time as the substrate, but not to the active site. In the presence of the inhibitor, the enzyme can bind the substrate but not catalyze the reaction. Because the inhibitor can not be driven from the enzyme by higher substrate concentration (in contrast to competitive inhibition), the apparent V<sub>max</sub> changes. But because the substrate can still bind to the enzyme, the K<sub>m</sub> stays the same.<ref name = "Cornish-Bowden_2004"/>{{rp|76–78}}
-*''[[Mixed inhibition|Mixed]]'': the binding of the substrate and the inhibitor affect each other. The enzyme's function is reduced but not eliminated when bound to the inhibitor. This type of inhibitor does not follow the Michaelis-Menten equation.<ref name = "Cornish-Bowden_2004"/>{{rp|76–78}}
-*''[[Irreversible inhibition|Irreversible]]'': the inhibitor permanently inactivates the enzyme, usually by forming a [[covalent bond]] to the protein. [[Penicillin]]<ref>{{vcite2 journal | vauthors = Fisher JF, Meroueh SO, Mobashery S | title = Bacterial resistance to beta-lactam antibiotics: compelling opportunism, compelling opportunity | journal = Chemical Reviews | volume = 105 | issue = 2 | pages = 395-424 | date = Feb 2005 | pmid = 15700950 | doi = 10.1021/cr030102i }}</ref> and [[aspirin]]<ref name="pmid9475035">{{vcite2 journal | vauthors = Sharma S, Sharma SC | title = An update on eicosanoids and inhibitors of cyclooxygenase enzyme systems | journal = Indian Journal of Experimental Biology | volume = 35 | issue = 10 | pages = 1025–31 | date = Oct 1997 | pmid = 9475035 | doi =  }}</ref> are common drugs that act in this manner.
 ===Functions of inhibitors===
@@ Line 164: / Line 160: @@
 There are four main ways that enzyme activity is controlled in the cell.<ref name = "Price_Stevnes_2000"> {{cite book | author = Price NC, Stevens L | title = Fundamentals of enzymology : the cell and molecular biology of catalytic proteins | date = 2000 | publisher = Oxford Univ. Press | location = Oxford | isbn = 0-19-850229-X | edition = 3 | chapter = Chapter 6: The control of enzyme activity | pages = 217–272 }}</ref>
-# ''Quantity:'' Enzyme production ([[Transcription (genetics)|transcription]] and [[Translation (genetics)|translation]] of enzyme genes) can be enhanced or diminished by a cell in response to changes in the cell's environment. This form of [[regulation of gene expression|gene regulation]] is called [[enzyme induction]]. For example, bacteria may become [[antibiotic resistance|resistant to antibiotics]] such as [[penicillin]] because enzymes called [[beta-lactamase]]s are induced that hydrolyse the crucial [[Beta-lactam|beta-lactam ring]] within the penicillin molecule.<ref name="pmid8452343">{{vcite2 journal | vauthors = Bennett PM, Chopra I | title = Molecular basis of beta-lactamase induction in bacteria | journal = Antimicrob. Agents Chemother. | volume = 37 | issue = 2 | pages = 153–8 | year = 1993 | pmid = 8452343 | pmc = 187630 | doi = | url = http://aac.asm.org/content/37/2/153.full.pdf }}</ref> Another example are enzymes in the [[liver]] called [[cytochrome P450 oxidase]]s, which are important in [[drug metabolism]]. Induction or inhibition of these enzymes can cause [[drug interaction]]s.<ref name = "Skett_Gibson_2001">{{cite book | author=Skett P, Gibson GG | title = Introduction to drug metabolism | date = 2001 | publisher = Nelson Thornes Publishers | location = Cheltenham, UK | isbn = 978-0748760114 | pages = 87–118| edition = 3 | chapter = Chapter 3: Induction and Inhibition of Drug Metabolism }}</ref>  Enzyme levels can also be regulated by changing the rate of enzyme [[catabolism|degradation]].
+; Quantity: Enzyme production ([[Transcription (genetics)|transcription]] and [[Translation (genetics)|translation]] of enzyme genes) can be enhanced or diminished by a cell in response to changes in the cell's environment. This form of [[regulation of gene expression|gene regulation]] is called [[enzyme induction]]. For example, bacteria may become [[antibiotic resistance|resistant to antibiotics]] such as [[penicillin]] because enzymes called [[beta-lactamase]]s are induced that hydrolyse the crucial [[Beta-lactam|beta-lactam ring]] within the penicillin molecule.<ref name="pmid8452343">{{vcite2 journal | vauthors = Bennett PM, Chopra I | title = Molecular basis of beta-lactamase induction in bacteria | journal = Antimicrob. Agents Chemother. | volume = 37 | issue = 2 | pages = 153–8 | year = 1993 | pmid = 8452343 | pmc = 187630 | doi = | url = http://aac.asm.org/content/37/2/153.full.pdf }}</ref> Another example are enzymes in the [[liver]] called [[cytochrome P450 oxidase]]s, which are important in [[drug metabolism]]. Induction or inhibition of these enzymes can cause [[drug interaction]]s.<ref name = "Skett_Gibson_2001">{{cite book | author=Skett P, Gibson GG | title = Introduction to drug metabolism | date = 2001 | publisher = Nelson Thornes Publishers | location = Cheltenham, UK | isbn = 978-0748760114 | pages = 87–118| edition = 3 | chapter = Chapter 3: Induction and Inhibition of Drug Metabolism }}</ref>  Enzyme levels can also be regulated by changing the rate of enzyme [[catabolism|degradation]].
-# ''Subcellular distribution:'' Enzymes can be compartmentalized, with different metabolic pathways occurring in different [[cellular compartment]]s. For example, [[fatty acids]] are synthesized by one set of enzymes in the [[cytosol]], [[endoplasmic reticulum]] and [[golgi]] and used by a different set of enzymes as a source of energy in the [[mitochondrion]], through [[β-oxidation]].<ref>{{vcite2 journal | vauthors = Faergeman NJ, Knudsen J | title = Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling | journal = The Biochemical Journal | volume = 323 ( Pt 1) | issue = Pt 1 | pages = 1–12  | date = Apr 1997 | pmid = 9173866 | pmc = 1218279 }}</ref> In addition, [[protein targeting|trafficking]] of the enzyme to different compartments may change the degree of [[protonation]] ([[cytoplasm]] neutral and [[lysosome]] acidic) or oxidative state [e.g., oxidized ([[periplasm]]) or reduced ([[cytoplasm]])] which in turn affects enzyme activity.<ref name = "Suzuki_2015_4">{{cite book | author = Suzuki H | title = How Enzymes Work: From Structure to Function | publisher = CRC Press | location = Boca Raton, FL | year = 2015 | isbn = 978-981-4463-92-8 | chapter = Chapter 4: Effect of pH, Temperature, and High Pressure on Enzymatic Activity | pages = 53–74 }}</ref>
+; Subcellular distribution: Enzymes can be compartmentalized, with different metabolic pathways occurring in different [[cellular compartment]]s. For example, [[fatty acids]] are synthesized by one set of enzymes in the [[cytosol]], [[endoplasmic reticulum]] and [[golgi]] and used by a different set of enzymes as a source of energy in the [[mitochondrion]], through [[β-oxidation]].<ref>{{vcite2 journal | vauthors = Faergeman NJ, Knudsen J | title = Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling | journal = The Biochemical Journal | volume = 323 ( Pt 1) | issue = Pt 1 | pages = 1–12  | date = Apr 1997 | pmid = 9173866 | pmc = 1218279 }}</ref> In addition, [[protein targeting|trafficking]] of the enzyme to different compartments may change the degree of [[protonation]] ([[cytoplasm]] neutral and [[lysosome]] acidic) or oxidative state [e.g., oxidized ([[periplasm]]) or reduced ([[cytoplasm]])] which in turn affects enzyme activity.<ref name = "Suzuki_2015_4">{{cite book | author = Suzuki H | title = How Enzymes Work: From Structure to Function | publisher = CRC Press | location = Boca Raton, FL | year = 2015 | isbn = 978-981-4463-92-8 | chapter = Chapter 4: Effect of pH, Temperature, and High Pressure on Enzymatic Activity | pages = 53–74 }}</ref>
-# ''[[Enzyme activator|Activation]]'' or ''[[enzyme inhibitor|inhibition]]:'' 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|negative feedback mechanism]], because the amount of the end product produced is regulated by its own concentration.<ref name = "Suzuki_2015_8"/>{{rp|141–48}}  Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps with effective allocations of materials and energy economy, and it prevents the excess manufacture of end products. Like other [[homeostasis|homeostatic devices]], the control of enzymatic action helps to maintain a stable internal environment in living organisms.
+; [[Enzyme activator|Activation]] or [[enzyme inhibitor|inhibition]]: 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|negative feedback mechanism]], because the amount of the end product produced is regulated by its own concentration.<ref name = "Suzuki_2015_8"/>{{rp|141–48}}  Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps with effective allocations of materials and energy economy, and it prevents the excess manufacture of end products. Like other [[homeostasis|homeostatic devices]], the control of enzymatic action helps to maintain a stable internal environment in living organisms.
-# ''[[Post-translational modification]]:'' These can include [[phosphorylation]], [[Myristic acid|myristoylation]] and [[glycosylation]].<ref name = "Suzuki_2015_8">{{cite book | author = Suzuki H | title = How Enzymes Work: From Structure to Function | publisher = CRC Press | location = Boca Raton, FL | year = 2015 | isbn = 978-981-4463-92-8 | chapter = Chapter 8: Control of Enzyme Activity | pages = 141–69 }}</ref>{{rp|149–69}} 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]].<ref name = "Doble_2003">{{vcite2 journal | vauthors = Doble BW, Woodgett JR | title = GSK-3: tricks of the trade for a multi-tasking kinase | journal = Journal of Cell Science | volume = 116 | issue = Pt 7 | pages = 1175–86  | date = Apr 2003 | pmid = 12615961 | pmc = 3006448 | doi = 10.1242/jcs.00384 }}</ref> 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. 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]].<ref name = "Suzuki_2015_8"/>{{rp|149–53}}
+; [[Post-translational modification]]: These can include [[phosphorylation]], [[Myristic acid|myristoylation]] and [[glycosylation]].<ref name = "Suzuki_2015_8">{{cite book | author = Suzuki H | title = How Enzymes Work: From Structure to Function | publisher = CRC Press | location = Boca Raton, FL | year = 2015 | isbn = 978-981-4463-92-8 | chapter = Chapter 8: Control of Enzyme Activity | pages = 141–69 }}</ref>{{rp|149–69}} 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]].<ref name = "Doble_2003">{{vcite2 journal | vauthors = Doble BW, Woodgett JR | title = GSK-3: tricks of the trade for a multi-tasking kinase | journal = Journal of Cell Science | volume = 116 | issue = Pt 7 | pages = 1175–86  | date = Apr 2003 | pmid = 12615961 | pmc = 3006448 | doi = 10.1242/jcs.00384 }}</ref> 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. 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]].<ref name = "Suzuki_2015_8"/>{{rp|149–53}}
 === Involvement in disease ===

v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)