What are enzymes? Types, chemical nature, Cofactor

What are enzymes?

 Enzymes are a type of biological catalyst that increases the rate of biochemical reactions. Proteins such as organic substances of nature that act as catalysts in living cells are called enzymes.

In 1897, Bergelyus Buchner first discovered the enzyme from a yeast cell, the first to use the term enzyme.

J.B. Sumner first crystallized the urease enzyme, for which Sumner was awarded the Nobel Prize.

The structure| Ribozyme

All enzymes are made up of proteins, some enzymes are made of RNA called ribozyme. The enzyme has many cleavages or sac-like structures called sites, activators are attached to these sites. Enzymes are different from inorganic catalysts such as inorganic catalysts at higher temperatures while enzymes are damaged at higher temperatures. Some enzymes that are found in organisms living in hot water sources, they remain active even at high temperature.

Chemical reactions and role of enzymes

There are two types of changes in chemical compounds –

  1. Physical changes: In these types of reactions, the chemical properties of compounds are unchanged, while the physical properties change.

Such as water from ice, vapor from water

  1. Chemical Transformation: In these types of reactions, bonds are broken in the compound and new bonds are formed, which changes the chemical properties of the compound.

Example: (i) Barium hydroxide reacts with sulfuric acid to form barium sulfate and water, it is an inorganic chemical reaction.

(ii) Starch decomposition into glucose is an example of an organic chemical reaction.

The rate of physical change and chemical change depends on the temperature and pressure.

The rate of physical changes and chemical reactions are affected more by temperature along with other factors.

By increasing or decreasing the temperature by 10 degrees, the reaction rate is doubled or halved.

Depending on the presence and absence of the catalyst, the reaction is of two types –

  1. Nonreactive Reactions: Reactions that take place under normal conditions without the presence of any catalyst are called non-reactive reactions.

Example – CO 2 + H 2 O = H 2 CO 3

  1. Catalyzed Reactions: Reactions that occur in the presence of a catalyst are called catalytic reactions.

Example: CO 2 + H 2 O = H 2 CO 3  (presence of carbonic anhydrate catalyst) (600000 molecules per second)

High rate chemical conversion by the enzyme

Chemical conversion takes place in the form of a reaction, the substances participating in the reaction are called reactants, the enzymes convert the reactants into products, the enzyme combines with the enzyme to form an enzyme reaction which is a temporary state, soon in the reaction cell. The bonds are broken and new bonds are formed, along with this, the products are released from the active site of the enzyme. The energy level difference between the base and the product can be displayed as a diagram.

The energy required to initiate a reaction is called inactivation energy. Enzymes reduce the energy required for the activation of molecules, that is, activate the molecule of the molecule at low energy. Whereas the enzyme-free reaction has high activation energy, in the presence of an enzyme, the reactants are converted into processes at low activation energy.

Nature of enzyme action

By joining the enzyme to the active site of the enzyme, the enzymes form the action class which disintegrates into the product and the unchanged enzyme.

The enzyme can express the catalytic cycle of action in the following steps –

  1. The first enzymes are added to the active site of the enzyme.
  2. The enzymes are strongly attached or joined by changes in the enzyme.
  3. Chemical bonds break down between enzyme enzymes and a new enzyme product complex is formed.
  4. The enzyme releases the newly formed product and becomes independent and ready to attach to another functional molecule, thus starting the catalytic cycle again.

Factors affecting enzyme mechanism

  1. Enzyme concentration: The reaction rate increases with increasing enzyme concentration, but the reaction rate also becomes constant when the concentration of the enzyme is constant.
  2. The concentration of reaction: The reaction rate also increases with increasing concentration of the enzyme, but the reaction rate becomes constant when the concentration of enzyme is limited.
  3. Temperature: The optimum temperature for enzyme action is from 20 ° C to 35 ° C, at temperatures above 35, enzymes are distorted which reduces the rate of the reaction.
  4. pH: Most enzymes work efficiently in the range of 5 to 7.5 PH, the rate of reaction is reduced when the pH value is low or high.
  5. Enzyme inhibitors: Substances that inactivate enzymes by activating their active sites are called enzyme inhibitors or inhibitors.

There are two types

  • Competitive inhibitors: The structure of such inhibitors is found in the action, so these substances compete with the functional molecules in joining the active sites of the enzyme, which slows down the activity of enzymes such as malic acid, succinic acid, etc.
  • Anti-inflammatory: This type of inhibitor attaches to the active sites of the enzyme and permanently distorts them. Such as Pb ++, Hg ++, Ag ++

Enzyme Nomenclature and Classification

Enzymes are named based on the chemical reactions they catalyze –

  1. Oxidoridacetase / D Hydrogenase: This class contains enzymes that catalyze oxidation and reduction reactions. Example – cytochrome oxidase
  2. Transferase: In this class, enzymes are placed which transfer groups other than H from one base to another.
  3. Hydrolase: Enzymes of this class catalyze reactions that add or remove water molecules, ie ester, ether, peptide, glycolytic, carbon-carbon, carbon halide, etc., to decompose the water. Examples – carbonic anhydrase, amylase
  4. Lysates: In addition to water decomposition, enzymes that break apart the binding of enzymes are placed in this class, which results in the formation of bonds, eg – histidine decarboxylase.
  5. Isomerase: Differences in this type of enzyme-catalyzed reactions that result in more rearrangements, changes in their potential, or optical equations.

Example – phospho haxo isomerase

  1. Ligases: This type of enzyme uses energy derived from ATP to catalyze reactions involving two compounds by covalent bonds. Example – Pyreneate carboxylase


Most enzymes are made up of proteins, but some enzymes are made up of proteins and the protein part, the protein part of the enzyme is called the apoenzyme and the a protein part.

Enzyme = apozyme + cofactor

Coenzyme: Organic substances that are temporarily linked to enzymes are called coenzymes, they are usually compounding like vitamins or vitamins.

Example: (i) Nicotinamide adenine dinucleotide (NAD)

(ii) Nicotinamide adenine dinucleotide phosphate (NADP)

Metal ion/activator: When the cofactor is inorganic (metal ion), it is called an activator.

Such as iron in cytochrome

Enzyme Enzymes are protein substances that are capable of catalyzing metabolic activity without changing them. They are also called organic catalysts or bio-catalysts.

More than 2000 enzymes have been known. Enzymes are produced in living cells, most of the enzymes work inside the cell where they are produced. These are called endogenous enzymes. On the other hand, the enzymes which act outside the cell are called exoenzymes. Digestive enzymes fall into this category.

Kirchoff first detected the presence of enzymes in the living system. Lewis Pasteur (1860) reported that the fermentation of sugars into alcohols by live yeast cells is stimulated by some substances that are in the yeast cells. They called these substances fermenters.

The enzyme was given by the name “W. Kuhne”.

Edward Büchner showed that yeast ferments cell sugars. Enzymes were thought to be responsible for this.

J.B. Summer (1926) purified and crystallized the enzyme urease, which acts as a catalyst in the ammonia and carbon dioxide water decomposition of urea. He explained that enzymes are made up of proteins. John Northrop and Knit crystallized pepsin, trypsin, and chymotrypsin.

Henson obtained renin which is used in milk at the time. Arbor, Smith, and Nathans received the Nobel Prize in 1978 for the discovery of restriction endonuclease that is used in DNA cutting in genetic engineering.

Chemical Nature of enzymes

What are enzymes? Types, chemical nature, Cofactor

All enzymes are protein in nature. By exception, ribozyme and ribonuclease enzymes are not protein in nature.

Thomas Ketch (1981) discovered the first RNA that functions as an enzyme. He called this ribozyme.

It was obtained from Tetrahyomina thermophile (protozoa) which distinguishes introns from newly formed RNA.

Sidney Altman (1983) discovered the ribonuclease-P enzyme (RNAase-P) that distinguishes tRNA from hnRNA.

Thomas Ketch and Sidney Altman received the Nobel Prize in 1989. A large number of enzymes in addition to the deproteinized group are required for their effective action.

In this way, there are two types of enzymes –

  1. Simple enzymes
  2. Conjugated enzyme
  3. Simple enzymes: Enzymes that are made up of only proteins. Examples: pepsin, trypsin, amylase, urease.
  4. Conjugated Enzymes: These enzymes are made up of two parts. The protein part is called apoenzyme and the protein part is called the co-factor. The whole conjugated enzyme holoenzyme, 
  5. for example hexokinase, decarboxylase in dehydrogenase.

Holozyme = epoenzyme + co-factor

Amino in the protein part describes the sequence, structure, and specificity of acids and the co-factor reflects the catalytic action of the enzyme and acts as a donor or receptor for the group or atom. If the co-factor is removed, the enzyme action is almost destroyed. Heating only affects the apoenzyme portion and the co-factor part remains unaffected. Even peptide bonds are not broken by heating. The bond controller breaks the three-dimensional structure.

Types of Co-factor

The co-factor can be isolated from the enzyme by dialysis. The co-factor can be organic or inorganic.

And there are three types (lehninger 1993)

(a)  Coenzyme (organic cofactor): These are weakly linked complex proteins, low molecular weight, thermogenic, organic, or cardiological groups that quickly dissociate from the apoenzyme. There are two types of these –

(i) Co-enzyme which acts as a hydrogen transfer. Examples: NAD, NADP, FMN, FAD, CoQ

(ii) The act of transferring a group in addition to H +. Examples: ATP, CoA, TPP, B 6, PO 4 , cobalamin, biotin are mainly made up of vitamin B complex, hence deficiency of these vitamins reduces the activity of these enzymes. Examples: NAD, NADP, TPP (thiamine pyrophosphate), CoA (coenzyme), FMN, FAD, coenzyme Q (ubiquinone), ATP, lipoic acid.

(b) Prostatic group (organic co-factor): It is the protein organic group of a hard and permanently attached metallic ion with a covalent bond that does not dissociate easily. Their task is to carry some groups. Unlike a co-enzyme, only one enzyme is required for prostatic group transfer. Examples: biotin, pyridoxal phosphate, and porphyrin of cytochrome, heme of hemoglobin.

(c) Inorganic  Co -Factor (metallic activator) : These essential elements are weakly attached to the apoenzyme portion of the enzyme. Example: Mn 2+ , Fe 2+ , Co 2+ , Zn 2+ , Mg 2+ , K + , Ca 2+ |

In some places, such as cytochrome iron, the metallic ion is strongly linked. Enzymes requiring metallic ions are called metallic enzymes.

Metallic ion Metalloenzyme

Fe 2+, Fe 3+ Cytochrome oxidase, catalase, peroxidase

Ca2+ Lipase, succinic dehydrogenase

Mg2+ Hexokinase, pyruvate kinase, DNA polymerase, enolase, phosphotransferase

Cu2+ Cytochrome oxidase, tyrosinase

Co2+ Ascorbic acid oxidase, peptidases

Mo Dinitrogenase, nitrate reductase

Mn 2+ Ribonucleotide reductase, Arginase

Zn 2+ Alcohol dehydrogenase, carbonic anhydrase, LDH, carboxypeptidase glycine reductase, thiolase

I know Glycine reductase, thiolase

K+ Pyruvate kinase

 Ni Urease

Cl– Salivary amylase

Na + ATPase

Enzymes Nomenclature

Naming enzymes is called nomenclature. There are three ways of naming enzymes –

  1. Duclaux (1883) gave a system of naming enzymes in which the suffix ‘edge’ is applied to the end of the substrate on which the enzyme functions or the type of reaction that the enzyme catalyzes.

(a) by adding a suffix: suffix ‘edge’ nomenclature of persistent enzyme example: sucrose, maltase, lipase, nuclease, peptidase (they act on sucrose, maltose, lipids, nucleic acids, polypeptides.)

(b) Depending on the function  : Example: dehydrogenase (removal of hydrogen), carboxylase (addition of carbon dioxide), decarboxylase (removal of carbon dioxide), oxidase (addition of oxygen), etc.

  1. Double nomenclature of an enzyme: In this, the name of the enzyme is given by two words. The first term is after the substrate and the second term is the work done by the enzyme. Example: Succinic dehydrogenase removes hydrogen from succinic acid.
  2. By Source: Some enzymes were nominated based on their source. Example: papain, which is obtained from the petiole of papaya. Bromelain is obtained from pineapple of the Bromillaceae clan. Papain protein is disruptive and also acts at high temperatures above 60 ° C.

However, some ancient names like Tilein, Pepsin, Trypsin are exceptions.

Classification of enzymes

According to the International Union of Biochemistry, enzymes are divided into six categories based on the type of reaction catalyzed –

category Catalyzed reaction


1. Oxidoridectase Transfer of electron from one substance to another on hydrogen and oxygen Succinic dehydrogenase, nitrate reductase

2. Transfers Transfer of a specific group (methyl, acyl, amino, or phosphate) from one substance to another Pyruvate transaminase, glucohexokinase

3. Hydrolase Decomposition of the long substrate into small parts by water Lipase, amylase, sucrose, lactase, peptide, estrogen, phosphatase, protease

4. Lyges Aqueous separation or coupling of the group with the substrate. CC, CN, CO, or CS can break the bond. Histidine decarboxylase

5. isomerase Changes in the relative form of the substrate by internal re-configuration Isomerases, epimarages, mutations

6. Syntheses The joining of two molecules by new CO, CS, CN, or CC bonds Acyls are enzymes A synthetase, pyruvate carboxylase, RUBP carboxylase PEP carboxylase

Properties of enzymes

  1. Protein nature: All enzymes are chemically made of protein. (Other than ribozyme and ribonuclease-P) These may however have additional organic or inorganic constituent functionalities.
  2. Amphotropic nature: Enzymes can ionize acids or bases based on the acidity of the external solution, so they are amphoteric. They can act as acids and bases.
  3. Colloidal nature: These are colloidal. Thus providing a large area for the reaction. This water is lubricating and forms hydrosols in the cell.
  4. Reversibility: Like real catalysts, enzymes can catalyze chemical reactions in any direction. Example: front and back reactions which depend on energy, pH, the concentration of products, and availability of reactants.

CH 3 CH 2 OH + NAD + → CH 3 CHO + NADH + H +

  1. Molecule: Enzyme protein is a substance with a high molecular weight. Peroxidase, the smallest enzyme, has a molecular mass of 40,000. While catalase is the longest enzyme, its molecular weight is 250,000. (Urease 483000)
  2. Specification of enzymes: enzymes are quite specific by nature. For example, a particular enzyme can only catalyze a particular reaction. The enzyme malic dehydrogenase can remove hydrogen from melic acid. Not from other Kito Amlo.

The specificity of the enzyme is determined by the sequence of amino acids at the active sites. The active space has a special bonded space that is coupled to the particular substrate. Thus a suitable substrate can fulfill the requirement of an active space and attach strongly to it.

  1. Unchanged form: Enzymes do not convert to any form in the chemical reaction nor do they come into use but remain unchanged at the end of the reaction.
  2. Chemical Reaction: Enzymes do not initiate a chemical reaction, but rather increase their speed. They also do not change the equilibrium. However, they increase speed and establish equilibrium quickly. Carbonic anhydrase is the fastest-acting enzyme.

CO2 + H2O → CO2 + H2O → H+ + HCO3–

This reaction is greatly slowed by the absence of an enzyme. About 200 molecules of H 2 CO 3 are produced in one hour. However, the reaction speed is increased by about 600,000 molecules per second by carbonic anhydrase, an enzyme present in the cytoplasm. The enzyme increases the reaction rate by about 10 million times.

  1. Efficiency: The capacity of an enzyme is determined by its “turnover number”. Such as the change in the number of molecules of the substrate from one enzyme molecule per minute.

It depends on the active regions present on the enzyme, the effective collision between the reactants, and the rate of removal of the products. The enzyme carbonyl anhydrate turnover number is 36 million, catalase 5 million, 10 thousand of sucrase or invertase, and 50 of flavoprotein.

How do enzymes speed up the reaction?

A certain amount of energy is required to initiate any chemical reaction. This is called activation energy. The molecules in each substrate have mostly average kinetic energy, some higher and some lower average energy molecules. At normal temperatures, molecules with relatively high energy react to form products, so the reaction is slow.

The temperature of the mixture can be increased to make the reaction faster. This increases the kinetic energy of the molecules, causing collisions and reactions. Another way to speed up the reaction is to add an enzyme. Enzyme reaction reduces the active energy and a large number of molecules react at the same time. Exactly how the enzyme works in active energy is not known. However, joining them with the enzyme-substrate molecule and bringing them closer, Completes the reaction at the appropriate direction and location by increasing the number of collisions. Inorganic catalysts work in this way. It is believed that celestial changes in the active region push the substrate molecule into action. Water decomposition of starch into glucose is an organic chemical reaction. The rate of a physical or chemical process increases the amount of product per unit of time. It is displayed as –

Rate = δp/δt

If the direction is known, then the rate is called velocity.

Information related to enzyme formation

It is surprising to know that at any given time in any cell, with an average diameter of 20 micrometers, there are thousands of different chemical reactions. Each reaction is catalyzed by a specific enzyme. How does the cell know which enzyme to produce?

The DNA of every cell is known to form every enzyme which enzymes are required. The cell uses this information when an enzyme is required for the reaction.

Place of enzyme action

All enzymes are produced in living cells. About 2000 enzymes have been known, based on their area of ​​action are classified in two ways –

  1. Intracellular
  2. Extracellular
  1. Intracellular enzymes: Maximum enzymes reside and function inside the cell. These are called endocrine enzymes or enzyme. Some cells are in a dissolved state. In liver cells, there are all 11 enzymes required for the transformation of glucose to lactic acid. Some enzymes bind to particles such as ribosomes, mitochondria, chloroplasts.

In mitochondria, there are soluble enzymes to make carbon dioxide and water from lactic acid.

  1. Extracellular or intracellular enzymes: Some enzymes function outside cells, called extracellular or exoenzyme. They mainly contain digestive enzymes. Examples: salivary amylase, gastric pepsin, pancreatic lipase, which secretes salivary gland, gastric gland, and pancreatic, respectively.

Lysozyme occurs in tear and nasal secretions.

Enzymes also carry their catalytic properties outside the cell. A rennet tablet containing the renin enzyme in the animal’s stomach is used to make cheese by quenching the milk protein carcinogen.

Mechanism of enzyme

Two concepts have been given to explain the enzyme mechanism –

  1. Key and lock concept: This concept is given by ‘Emil Fisher (1894)’. Accordingly, both substrate and enzyme molecules have a special geometric structure.

It is similar to the lock and key system. Which has a special geometric shape in place of the verb. The active region holds special groups -NH 2, -COOH, -SH, which interact with the substrate molecule.

Just as a lock can be opened by a particular key, the molecule of a substrate is activated by a particular enzyme. This explains the specificity of enzyme action. The substrate molecule or reactant, when exposed to the active region of the enzyme, forms a compound enzyme-substrate complex (complex).

Molecules of the substrate in the enzyme-substrate complex form products after chemical transformation.

The product does not stay in the active area for long periods and diffuses into the atmosphere. During this time it frees the active region and leaves it bound to another substrate molecule. This assumption demonstrates how small amounts of enzymes act on large amounts of substrate. It also explains how the enzyme remains unchanged at the end of the reaction. Accordingly, it can also be explained how a substance with the same structure as the substrate acts as a competitive inhibitor.

  1. Inspired adjusted (fit) concept: given by Koshland (1960). Accordingly, the active region of the enzyme is not initially complementary to the substrate in shape but rather takes the complementary shape after the substrate is joined to the enzyme. According to Koshland, the active area is driven to a complementary shape in the same way that the hand changes the shape of the gloves. The active region of the enzyme is the pocket to which the substrate binds. Thus the enzyme catalyzes the reaction at a high rate by its active region. Thus, the enzyme is flexible. There are two groups on the active region of an enzyme.

(a) Buttressing group: which is to support the substrate.

(b) catalytic group: which catalyzes the reaction. When the substrate comes in contact with the buttressing group, the active region changes, the catalytic group breaks the bond from the opposite side of the substrate bond.

Factors affecting enzyme activity

  1. PH: The catalytic property of an enzyme acts only within a limited pH range. The reactivity in this range is maximized at a specific pH, called optimal pH, and then drops again. Each enzyme has its own optimum pH.

The optimum pH of gastric juice pepsin is 2.0 while the maximum activity of trypsin is observed at pH 8.5 and sucrose at pH 4.5.

However, most of the endocrine enzymes exhibit maximum reactivity between pH 6.5 to 7.5. (Near neutral pH) Enzymes are other than urease function in a narrow pH range. The sudden change in pH affects the protein and breaks down the hydrogen and other bonds that make up the tertiary structure of the enzyme.

  1. Temperature: Each enzyme has a specific optimum temperature. According to the general rule, the value of Q 10 (temperature coefficient) is 2 -3. For example, between the minimum and optimum temperature (5–40 ° C), the speed of the reaction increases 2-3 times upon increasing the temperature to 10 ° C.

Enzymes become inactive if the heat is moved near or below the deposition point. The maximum enzyme exhibits its maximum action temperature between 25–40 ° C. Enzymes are heat sensitive.

Breaks at higher temperatures. The loss of catalytic properties starts at 35 ° C and is completed at 60 ° C. However, dry enzyme extraction also survives at temperatures of 100–120 ° C. Therefore, dry seeds can tolerate higher temperatures than sprouted seeds. Heat stability is thus an important property of enzymes dissociated from heat-loving organisms. Example: Taq. polymerase

  1. Substrate concentrations: The rate of product formation increases for a certain time by increasing the concentration of the substrate. Finally at a point when the enzymes become saturated with the substrate. Increasing substrate concentrations at this point does not affect the rate of product formation. If we look at the graph between the substrate concentration and the reaction velocity, it is the parabolic curve. The velocity at one state is maximized. This substrate does not grow on increasing concentration. At this stage, enzyme molecules become fully saturated. And no active area is available. All enzymes show this saturating effect.

Micelles constant (Micelles Menton constant, Km ): It is the constant that indicates the concentration of the substrate at which the enzyme’s catalytic chemical action takes up half its maximum velocity. The micelles maintenance constant is usually between 10 -1 to 10 -6 M.

High Km denotes low fraternity while low K denotes high fraternity. If an enzyme acts on more than one substrate, it shows different Km values ​​for them.

This Michaelis Menton equation is as follows –

Thus the value of Km is proportional to the concentration of the substrate at which the reaction speed is half of the maximum. The value of the Michaelis Menton constant is inversely proportional to the enzyme action.

 A higher value of Km means that the concentration of the substrate will be higher to obtain half the velocity of the maximum speed of the reaction.

Simply put, this implies that the enzyme has a reduced affinity to the substrate. If the curve is drawn between the inverse value of enzyme action and substrate concentration, we get a straight line. In this plot, the value of K m can be obtained by increasing the line in the posterior direction.

  1. Enzyme concentrations: If more substrate is present than required, doubling the enzyme doubles the reaction rate. This is only appropriate at the start of the reaction because the end product of the reaction often hurts the enzyme and reduces its effectiveness.
  2. Product concentration: As the product collects, the reaction speed decreases.
  3. Heavy metals: Some metals convert enzymes into inert form. Examples: Ag, Zn, Cu, Pb, and Cd, etc.

Activation energy

Most chemical reactions do not start spontaneously because reactant molecules have energy inhibitors that are activated only by obtaining them. Energy inhibitors occur in many ways –

  1. Due to the mutual repulsion of electrons present on their surface.
  2. If the sites of active molecules are small then proper collision does not occur. Such reactions take energy from outside. This is called activation energy.

The activation energy increases the kinetic energy of the system and makes it effective inactivators. Activation energy is required. Example: Acidic water decomposition of sucrose takes about 32000 cal/mole of energy. As we know there are thousands of chemical reactions in the cell, so the activation energy required for such reactions cannot be provided by the living system. The enzyme decreases the activation energy of the reaction. Example: Water decomposition of sucrose takes 9000 cal/mole of energy in the presence of enzyme sucrase or invertase (instead of 32000 cal/mole)

Proenzyme or zymogen

Inactive are pre-formed parts of proenzyme. The term zymogen is commonly used to denote the inactive state of protein degrading enzymes. Example: pepsinogen for the enzyme pepsin. Enzymes are initially produced in the proenzyme or zymogen state. They are functional only after a certain pH, availability of substrate, or special treatment. Example: Pepsinogen changes in the active enzyme pepsin in the presence of HCl of gastric juice. The subsequent transformation is followed by the self-catalytic effect of pepsin.

Allosteric enzyme

Enzymes that contain certain locations that bind to various chemicals and change the structure of the active site make them effective or ineffective. These alter alastoric sites, called modulators or allosteric substances. These are of two types. Activator and inhibitor. Allosteric activators connect to the allosteric site in such a way that the actives make the site actuarial. Allosteric inhibitors, on the other hand, make changes in the activator site such that they are not able to bind to substrate molecules. Example: The enzyme phosphofructokinase is activated by ADP and inhibited by ATP.


In the past, it was believed that an organism contained only one enzyme for one term of a metabolic reaction. Later it was discovered that more than one enzyme can also act on a substrate to form a similar product. An enzyme in the same organism with a different molecular structures and similar substrate reactivity is called isoenzyme or isozyme. The isoenzymes of more than 100 enzymes are known. Thus, 16 isozymes of alpha-amylase of wheat endosperm contain 5 isozymes of lactic dehydrogenase in humans and 4 isozymes of alcohol dehydrogenase in maize. Isozymes differ in their activity and inhibition. It helps the organism to adapt to environmental conditions.

Inhibition of enzyme activity: enzyme activity is inhibited in four ways –

  1. Denaturation
  2. Competitive blocking
  3. Incompetent interception
  4. Allosteric inhibition
  5. Denaturation: At 55 to 60 ° C, high temperature changes its unique structure by changing the stereoscopic arrangement of the polypeptide chain within the protein molecule. As a result, physical and biological properties change. Denaturation of the enzyme is an example of irreversible inhibition.
  6. Competitive Blocking: This is usually the case because more substrate volume reduces the effect of blocking. In this type of blocking the inhibitor is similar to the substrate in the structure and competes with the substrate at the active site. Thus it inhibits the forward reaction. The binding of these enzymes to the inhibitor or substrate depends on the concentration of the substrate and the inhibitor. The amount of inhibition can be reduced by increasing the concentration of the substrate. The presence of a competitive inhibitor increases Km. Example: Synthesis of colic acid, a sulfa drug in bacteria, prevents competition by para amino benzoic acid. The action of the succinate dehydrogenase enzyme is inhibited by malonic acid from competing with succinate acid.

Inhibition is important and it is not metabolized by enzymes analogous to the lock key concept of enzyme action.

  1. Non-binding inhibitionInhibition of enzyme action in the presence of a substance that does not show structural similarity with the substrate. Nonreactive inhibitors inhibit enzyme action by irreversibly joining or destroying the functional group of the enzyme.

This inhibitor reduces V max but Km does not change. Increasing substrate concentrations do not affect inhibition. Example: Cyanide inhibits the action of cytochrome oxidase. It has no structural resemblance to an enzyme called cytochrome c. Cytochrome oxidase is a putative enzyme. In this interception, animals die due to the inability to breathe.

The amino acid of the di-isopropyl fluorophosphate acetylcholine esterase inhibits impulse translocation by associating with serine.

  1. Allosteric Blockage :

(i) Feedback inhibition or allosteric modulation: It is reversible irreversible inhibition that occurs in allosteric enzymes. These inhibitors are generally intermediate of the product of the reactions catalyzed by the enzymes. Thus allosteric blocking is called end product blocking, feedback or retro blocking. Product inhibitors function like negative modulators. These join at the inhibitor site and make allosteric changes at the active site.

(ii) The enzymes hexokinase, glucokinase also ATP: D-glucose phosphotransferase form glucose 6-phosphate in the forward reaction.

(iii) In the bacterium Escherichia coli, the three-phase reaction in threonine amino acids, isoleucine converts to the enzyme-controlled state. The accumulation of isoleucine due to non-absorption from outside prevents this change, as allosteric inhibition of the first termed enzyme threonine disease occurs.

Importance of enzyme inhibition

  • Feedback blocking controls the overproduction of the product.
  • Enzyme inhibition is useful in the study of metabolic functions.
  • It shows the mechanism of the enzyme.
  • Sulfonamide or sulfur drugs, used in colic acid synthesis, have been produced based on the inhibitory action of prokaryotic enzymes.
  • Malathion and many more insecticides have been made based on inhibitory action on their nervous flow.

Some important facts related to enzymes

  • ELISA: This enzyme is immunosorbent when a protein, antibody or antigen is tested by enzymes, eg: AIDS.
  • Protease: Used in washing clothes after putting in detergent and amylase is also used for washing dishes in detergent.
  • Allozyme: Made by different enzymes.
  • Producing enzymes are always present because they are required in biological functions: Example: glycolysis
  •  The decomposition of the K i enzyme-inhibitor complex is a constant. It is suitable for competitive inhibitors. Low K i is required for enzyme activity while high K I decreases it.
  • The antibody which acts as an enzyme is called Abzimes.
  • The study of enzymes and their functions is called enzymology.
  • The first known enzyme was diastase.
  • Maximum enzymes are found in individuals.
  • Myosin is a contractile protein that has both structural and enzymatic functions. (ATPase is the verb.)
  • As an enzyme marker  :

(i) Saxinic dehydrogenase and glutamate dehydrogenase are mitochondrial markers.

(ii) Acid phosphatase is a lysosomal marker.

(iii) The ribosome marker is RNA.

(iv) Cytochrome oxidase is a marker enzyme of the intracellular membrane.

What are enzymes? Types, chemical nature, Cofactor

What are enzymes? Types, chemical nature, Cofactor


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