What does an enzyme consist of? and what causes such selective properties of it!?

Back in the 19th century, it was assumed that the main component that makes up the enzyme is protein. In the 20th century, another repeated attempt was made in Germany to find out what does an enzyme consist of?. It was erroneously assumed that enzymes could not be classified as proteins or any other organic substance. A little later, the enzyme was obtained in America "urease" in the form of protein crystals, but this experiment was invalidated due to distortion of the experiment.

Only in the 30s of the 20th century were enzymes obtained, such as trypsin And pepsin in crystalline form, after which their protein structure was recognized, which 20 years later was confirmed by X-ray structural analysis.

Proteins are complex organic substances with a very complex structure. They can have up to 4 different structural levels. So, if a protein consists of several chains connected to each other, then such a structure will be called quaternary. For example, an enzyme has this structure alcohol dehydrogenase yeast. If at least one protein level is disrupted, this causes denaturation of the protein; an acidic environment destroys bonds and disulfide bridges inside protein molecules. If the temperature increases, the helices in which protein molecules are folded begin to unfold, which leads to the loss of the catalytic properties of enzymes. This explains such sensitivity to the operating conditions of enzymes.

(the protein properties page is dedicated to proteins)

But as it turned out, enzyme consists of more than just protein. In addition to the protein, another organic residue or even a metal ion may also be present. It is interesting that it is precisely those enzymes containing such “inclusions” (metals or other organic residues) that are able to exhibit activity and be real catalysts for chemical reactions. The part of the enzyme molecule that contains such inclusions is called enzyme (this name was given in 1897, when manganese was discovered in the ash of the enzyme laccases.

Our body itself produces the proteins necessary for us, characteristic only of our body, but coenzymes are synthesized with difficulty, since metals enter our body in the required quantities mainly with vitamins and microelements. Vitamins are very necessary for our body, as they contain metals and contribute to the formation of capable enzymes.

(You can read more about vitamins on the page Vitamins and food supplements, where a detailed description of the vitamins we use and the food in which they can be found is given. The normal human body contains ions of various metals, and for a person weighing 70 kg it is necessary for normal life activity 2 .3 g zinc (Zn), 4.1 g iron (Fe), 0.2 g copper (Cu), as well as many other trace elements: magnesium, molybdenum, cobalt, calcium, potassium, sodium.

For example, in the body iron forms complex compounds and is an integral part of the enzyme peroxidases And catalase(this enzyme catalyzes the chemical oxidation reaction between hydrogen peroxide and organic substances). But in order for our body to better process and break down alcohol (this is performed by the enzyme alcohol dehydrogenase and carbonic anhydrase), we need zinc.

How do enzymes arise?

People have solved amazing and useful properties of enzymes long before their opening. People did not yet know how to obtain and secrete enzymes, but they already knew what substances had catalytic action For example, elements of living nature were widely used to ferment wine, prepare dough, and curd milk (for example, the same yeast for making alcohol). Certainly, live enzymes(obtained from animal and plant tissues) are still used today, but a more interesting and modern direction is the isolation pure enzymes. For example, in the washing powders we know, which wash away any grease stains well, special types of enzymes have been added that can easily dissolve and not spoil the fabric.

The vast majority of enzymes we use are formed by individual types of microorganisms. The enzymes formed in this way can be obtained in almost unlimited quantities. It all depends on the environment and habitat of microorganisms, which we ourselves can, if desired, control.

Enzyme production in application to the broad needs of the people was organized at the end of the 19th century. But only after the mid-20th century, with the development of bioengineering, it became possible to realize all the needs of society for enzymes and open their mass production.

In applied applications, the enzyme is taken in very small quantities to carry out a chemical reaction. For example, to turn a boiled chicken egg (white) into a set of amino acids and convert them into solution, you only need 1 g of enzyme pepsin and 2 hours time.

In our body, DNA is responsible for the production of enzymes. A certain sequence of structural components of DNA, built into a bacterial molecule, will allow us to obtain bacteria that will produce the necessary enzyme - as according to a strict program

ChapterIV.3.

Enzymes

Metabolism in the body can be defined as the totality of all chemical transformations to which compounds coming from outside undergo. These transformations include all known types of chemical reactions: intermolecular transfer of functional groups, hydrolytic and non-hydrolytic cleavage of chemical bonds, intramolecular rearrangement, new formation of chemical bonds and redox reactions. Such reactions occur in the body at extremely high speed only in the presence of catalysts. All biological catalysts are substances of protein nature and are called enzymes (hereinafter F) or enzymes (E).

Enzymes are not components of reactions, but only accelerate the achievement of equilibrium by increasing the rate of both direct and reverse conversion. Acceleration of the reaction occurs due to a decrease in the activation energy - the energy barrier that separates one state of the system (the original chemical compound) from another (the reaction product).

Enzymes speed up a variety of reactions in the body. So, quite simple from the point of view of traditional chemistry, the reaction of the elimination of water from carbonic acid with the formation of CO 2 requires the participation of an enzyme, because without it, it proceeds too slowly to regulate blood pH. Thanks to the catalytic action of enzymes in the body, it becomes possible for reactions to occur that without a catalyst would proceed hundreds and thousands of times slower.

Properties of enzymes

1. Influence on the rate of a chemical reaction: enzymes increase the rate of a chemical reaction, but are not consumed themselves.

The rate of a reaction is the change in the concentration of reaction components per unit time. If it goes in the forward direction, then it is proportional to the concentration of the reactants, if in the opposite direction, then it is proportional to the concentration of the reaction products. The ratio of the rates of forward and reverse reactions is called the equilibrium constant. Enzymes cannot change the values ​​of the equilibrium constant, but the state of equilibrium occurs faster in the presence of enzymes.

2. Specificity of enzyme action. 2-3 thousand reactions take place in the cells of the body, each of which is catalyzed by a specific enzyme. The specificity of an enzyme's action is the ability to accelerate the course of one specific reaction without affecting the speed of others, even very similar ones.

There are:

Absolute– when F catalyzes only one specific reaction ( arginase– breakdown of arginine)

Relative(group special) – F catalyzes a certain class of reactions (for example, hydrolytic cleavage) or reactions involving a certain class of substances.

The specificity of enzymes is due to their unique amino acid sequence, which determines the conformation of the active center that interacts with the reaction components.

A substance whose chemical transformation is catalyzed by an enzyme is called substrate ( S ) .

3. Enzyme activity – the ability to accelerate the reaction rate to varying degrees. Activity is expressed in:

1) International units of activity - (IU) the amount of enzyme that catalyzes the conversion of 1 µM of substrate in 1 minute.

2) Catalach (kat) - the amount of catalyst (enzyme) capable of converting 1 mole of substrate in 1 s.

3) Specific activity - the number of activity units (any of the above) in the test sample to the total mass of protein in this sample.

4) Less commonly used is molar activity - the number of substrate molecules converted by one enzyme molecule per minute.

Activity depends primarily on temperature . This or that enzyme exhibits its greatest activity at the optimal temperature. For F of a living organism, this value is in the range +37.0 - +39.0° C, depending on the type of animal. As the temperature decreases, the Brownian motion slows down, the diffusion rate decreases and, consequently, the process of complex formation between the enzyme and the reaction components (substrates) slows down. If the temperature rises above +40 - +50° The enzyme molecule, which is a protein, undergoes a process of denaturation. In this case, the rate of the chemical reaction noticeably drops (Fig. 4.3.1.).

Enzyme activity also depends on pH of the environment . For most of them, there is a certain optimal pH value at which their activity is maximum. Since a cell contains hundreds of enzymes and each of them has its own pH limits, pH changes are one of the important factors in the regulation of enzymatic activity. So, as a result of one chemical reaction with the participation of a certain enzyme, the pH value of which lies in the range of 7.0 - 7.2, a product is formed that is an acid. In this case, the pH value shifts to the region of 5.5 – 6.0. The activity of the enzyme decreases sharply, the rate of product formation slows down, but at the same time another enzyme is activated, for which these pH values ​​are optimal and the product of the first reaction undergoes further chemical transformation. (Another example about pepsin and trypsin).

Chemical nature of enzymes. The structure of the enzyme. Active and allosteric centers

All enzymes are proteins with a molecular weight from 15,000 to several million Da. According to their chemical structure they are distinguished simple enzymes (consisting only of AA) and complex enzymes (have a non-protein part or a prosthetic group). The protein part is called - apoenzyme, and non-protein, if it is covalently linked to the apoenzyme, it is called coenzyme, and if the bond is non-covalent (ionic, hydrogen) – cofactor . The functions of the prosthetic group are as follows: participation in the act of catalysis, contact between the enzyme and the substrate, stabilization of the enzyme molecule in space.

The role of cofactor is usually played by inorganic substances - ions of zinc, copper, potassium, magnesium, calcium, iron, molybdenum.

Coenzymes can be considered as an integral part of the enzyme molecule. These are organic substances, among which there are: nucleotides ( ATP, UMF, etc.), vitamins or their derivatives ( TDF– from thiamine ( IN 1), FMN– from riboflavin ( AT 2), coenzyme A– from pantothenic acid ( AT 3), NAD, etc.) and tetrapyrrole coenzymes - hemes.

In the process of catalyzing a reaction, not the entire enzyme molecule comes into contact with the substrate, but a certain part of it, which is called active center. This zone of the molecule does not consist of a sequence of amino acids, but is formed by twisting the protein molecule into a tertiary structure. Individual sections of amino acids come closer to each other, forming a specific configuration of the active center. An important feature of the structure of the active center is that its surface is complementary to the surface of the substrate, i.e. AK residues in this zone of the enzyme are capable of entering into chemical interactions with certain groups of the substrate. One can imagine that The active site of the enzyme coincides with the structure of the substrate like a key and a lock.

IN active center two zones are distinguished: binding center, responsible for substrate attachment, and catalytic center, responsible for the chemical transformation of the substrate. The catalytic center of most enzymes includes AAs such as Ser, Cys, His, Tyr, Lys. Complex enzymes have a cofactor or coenzyme at the catalytic center.

In addition to the active center, a number of enzymes are equipped with a regulatory (allosteric) center. Substances that affect its catalytic activity interact with this zone of the enzyme.

Mechanism of action of enzymes

The act of catalysis consists of three successive stages.

1. Formation of an enzyme-substrate complex upon interaction through the active center.

2. Binding of the substrate occurs at several points in the active center, which leads to a change in the structure of the substrate and its deformation due to changes in the bond energy in the molecule. This is the second stage and is called substrate activation. In this case, a certain chemical modification of the substrate occurs and it is converted into a new product or products.

3. As a result of this transformation, the new substance (product) loses its ability to be retained in the active center of the enzyme and the enzyme-substrate, or rather, enzyme-product complex dissociates (breaks up).

Types of catalytic reactions:

A+E = AE = BE = E + B

A+B +E = AE+B = ABE = AB + E

AB+E = ABE = A+B+E, where E is the enzyme, A and B are substrates or reaction products.

Enzymatic effectors - substances that change the rate of enzymatic catalysis and thereby regulate metabolism. Among them there are inhibitors - slow down the reaction rate and activators - accelerating the enzymatic reaction.

Depending on the mechanism of reaction inhibition, competitive and non-competitive inhibitors are distinguished. The structure of the competitive inhibitor molecule is similar to the structure of the substrate and coincides with the surface of the active center like a key and a lock (or almost coincides). The degree of this similarity may even be higher than with the substrate.

If A+E = AE = BE = E + B, then I+E = IE¹

The concentration of the enzyme capable of catalysis decreases and the rate of formation of reaction products drops sharply (Fig. 4.3.2.).

A large number of chemical substances of endogenous and exogenous origin (i.e., those formed in the body and coming from outside - xenobiotics, respectively) act as competitive inhibitors. Endogenous substances are regulators of metabolism and are called antimetabolites. Many of them are used in the treatment of oncological and microbial diseases, as. they inhibit key metabolic reactions of microorganisms (sulfonamides) and tumor cells. But with an excess of substrate and a low concentration of the competitive inhibitor, its effect is canceled.

The second type of inhibitors is non-competitive. They interact with the enzyme outside the active site and excess substrate does not affect their inhibitory ability, as is the case with competitive inhibitors. These inhibitors interact either with certain groups of the enzyme (heavy metals bind to the thiol groups of Cys) or most often with the regulatory center, which reduces the binding ability of the active center. The actual process of inhibition is the complete or partial suppression of enzyme activity while maintaining its primary and spatial structure.

A distinction is also made between reversible and irreversible inhibition. Irreversible inhibitors inactivate the enzyme by forming a chemical bond with its AK or other structural components. This is usually a covalent bond to one of the active site sites. Such a complex practically does not dissociate under physiological conditions. In another case, the inhibitor disrupts the conformational structure of the enzyme molecule and causes its denaturation.

The effect of reversible inhibitors can be removed when there is an excess of substrate or under the influence of substances that change the chemical structure of the inhibitor. Competitive and non-competitive inhibitors are in most cases reversible.

In addition to inhibitors, activators of enzymatic catalysis are also known. They:

1) protect the enzyme molecule from inactivating influences,

2) form a complex with the substrate that binds more actively to the active center of F,

3) interacting with an enzyme that has a quaternary structure, they separate its subunits and thereby open up access for the substrate to the active center.

Distribution of enzymes in the body

Enzymes involved in the synthesis of proteins, nucleic acids and energy metabolism enzymes are present in all cells of the body. But cells that perform special functions also contain special enzymes. Thus, the cells of the islets of Langerhans in the pancreas contain enzymes that catalyze the synthesis of the hormones insulin and glucagon. Enzymes that are characteristic only of the cells of certain organs are called organ-specific: arginase and urokinase- liver, acid phosphatase- prostate. By changing the concentration of such enzymes in the blood, the presence of pathologies in these organs is judged.

In a cell, individual enzymes are distributed throughout the cytoplasm, others are embedded in the membranes of mitochondria and the endoplasmic reticulum, such enzymes form compartments, in which certain, closely interconnected stages of metabolism occur.

Many enzymes are formed in cells and secreted into anatomical cavities in an inactive state - these are proenzymes. Proteolytic enzymes (that break down proteins) are often formed as proenzymes. Then, under the influence of pH or other enzymes and substrates, their chemical modification occurs and the active center becomes accessible to the substrates.

There are also isoenzymes - enzymes that differ in molecular structure, but perform the same function.

Nomenclature and classification of enzymes

The name of the enzyme is formed from the following parts:

1. name of the substrate with which it interacts

2. nature of the catalyzed reaction

3. name of the enzyme class (but this is optional)

4. suffix -aza-

pyruvate - decarboxyl - aza, succinate - dehydrogen - aza

Since about 3 thousand enzymes are already known, they need to be classified. Currently, an international classification of enzymes has been adopted, which is based on the type of reaction catalyzed. There are 6 classes, which in turn are divided into a number of subclasses (presented only selectively in this book):

1. Oxidoreductases. Catalyze redox reactions. They are divided into 17 subclasses. All enzymes contain a non-protein part in the form of heme or derivatives of vitamins B2, B5. The substrate undergoing oxidation acts as a hydrogen donor.

1.1. Dehydrogenases remove hydrogen from one substrate and transfer it to other substrates. Coenzymes NAD, NADP, FAD, FMN. They accept the hydrogen removed by the enzyme, transforming it into a reduced form (NADH, NADPH, FADH) and transfer it to another enzyme-substrate complex, where they release it.

1.2. Oxidases - catalyze the transfer of hydrogen to oxygen to form water or H 2 O 2. F. Cytochrome oxidase respiratory chain.

RH + NAD H + O 2 = ROH + NAD + H 2 O

1.3. Monoxidases - cytochrome P450. According to its structure, it is both a hemoprotein and a flavoprotein. It hydroxylates lipophilic xenobiotics (according to the mechanism described above).

1.4. PeroxidasesAnd catalase- catalyze the decomposition of hydrogen peroxide, which is formed during metabolic reactions.

1.5. Oxygenases - catalyze reactions of oxygen addition to the substrate.

2. Transferases - catalyze the transfer of various radicals from a donor molecule to an acceptor molecule.

A A+ E + B = E A+ A + B = E + B A+ A

2.1. Methyltransferase (CH 3 -).

2.2.Carboxyl- and carbamoyltransferases.

2.2. Acyltransferases – Coenzyme A (transfer of acyl group - R -C=O).

Example: synthesis of the neurotransmitter acetylcholine (see chapter “Protein Metabolism”).

2.3. Hexosyltransferases catalyze the transfer of glycosyl residues.

Example: the cleavage of a glucose molecule from glycogen under the influence of phosphorylases.

2.4. Aminotransferases - transfer of amino groups

R 1- CO - R 2 + R 1 - CH - N.H. 3 - R 2 = R 1 - CH - N.H. 3 - R 2 + R 1- CO - R 2

They play an important role in the transformation of AK. The common coenzyme is pyridoxal phosphate.

Example: alanine aminotransferase(ALT): pyruvate + glutamate = alanine + alpha-ketoglutarate (see chapter “Protein Metabolism”).

2.5. Phosphotransferase (kinase) - catalyze the transfer of a phosphoric acid residue. In most cases, the phosphate donor is ATP. Enzymes of this class mainly take part in the breakdown of glucose.

Example: Hexo(gluco)kinase.

3. Hydrolases - catalyze hydrolysis reactions, i.e. splitting of substances with addition at the site where the water bond is broken. This class includes mainly digestive enzymes; they are single-component (do not contain a non-protein part)

R1-R2 +H 2 O = R1H + R2OH

3.1. Esterases - break down ester bonds. This is a large subclass of enzymes that catalyze the hydrolysis of thiol esters and phosphoesters.
Example: NH 2 ).

Example: arginase(urea cycle).

4.Lyases - catalyze reactions of molecular splitting without adding water. These enzymes have a non-protein part in the form of thiamine pyrophosphate (B 1) and pyridoxal phosphate (B 6).

4.1. C-C bond lyases. They are usually called decarboxylases.

Example: pyruvate decarboxylase.

5.Isomerases - catalyze isomerization reactions.

Example: phosphopentose isomerase, pentose phosphate isomerase(enzymes of the non-oxidative branch of the pentose phosphate pathway).

6.Ligases catalyze reactions for the synthesis of more complex substances from simpler ones. Such reactions require the energy of ATP. “Synthetase” is added to the name of such enzymes.

REFERENCES FOR THE CHAPTER IV.3.

1. Byshevsky A. Sh., Tersenov O. A. Biochemistry for the doctor // Ekaterinburg: Uralsky Rabochiy, 1994, 384 pp.;

2. Knorre D. G., Myzina S. D. Biological chemistry. – M.: Higher. school 1998, 479 pp.;

3. Filippovich Yu. B., Egorova T. A., Sevastyanova G. A. Workshop on general biochemistry // M.: Enlightenment, 1982, 311 pp.;

4. Leninger A. Biochemistry. Molecular basis of cell structure and functions // M.: Mir, 1974, 956 pp.;

5. Pustovalova L.M. Workshop on biochemistry // Rostov-on-Don: Phoenix, 1999, 540 p.

· Structure and mechanism of action of enzymes · Multiple forms of enzymes · Medical significance · Practical use · Notes · Literature ·

The activity of enzymes is determined by their three-dimensional structure.

Like all proteins, enzymes are synthesized in the form of a linear chain of amino acids, which folds in a certain way. Each sequence of amino acids folds in a special way, and the resulting molecule (protein globule) has unique properties. Several protein chains can be combined to form a protein complex. The tertiary structure of proteins is destroyed by heat or exposure to certain chemicals.

Active site of enzymes

The study of the mechanism of a chemical reaction catalyzed by an enzyme, along with the determination of intermediate and final products at different stages of the reaction, implies precise knowledge of the geometry of the tertiary structure of the enzyme, the nature of the functional groups of its molecule, providing specificity of action and high catalytic activity on this substrate, and in addition the chemical nature of the site ( sites) of an enzyme molecule that provides a high rate of catalytic reaction. Typically, the substrate molecules involved in enzymatic reactions are relatively small in size compared to enzyme molecules. Thus, during the formation of enzyme-substrate complexes, only limited fragments of the amino acid sequence of the polypeptide chain enter into direct chemical interaction - the “active center” - a unique combination of amino acid residues in the enzyme molecule, ensuring direct interaction with the substrate molecule and direct participation in the act of catalysis.

The active center is conventionally divided into:

• catalytic center - directly chemically interacting with the substrate;
• binding center (contact or “anchor” site) - providing specific affinity for the substrate and the formation of the enzyme-substrate complex.

To catalyze a reaction, an enzyme must bind to one or more substrates. The protein chain of the enzyme folds in such a way that a gap, or depression, is formed on the surface of the globule where substrates bind. This region is called the substrate binding site. It usually coincides with or is close to the active site of the enzyme. Some enzymes also contain binding sites for cofactors or metal ions.

The enzyme combines with the substrate:

• cleans the substrate from water “coat”
• arranges reacting substrate molecules in space in the manner necessary for the reaction to occur
• prepares substrate molecules for reaction (for example, polarizes).

Usually, the enzyme attaches to the substrate through ionic or hydrogen bonds, rarely through covalent bonds. At the end of the reaction, its product (or products) are separated from the enzyme.

As a result, the enzyme reduces the activation energy of the reaction. This happens because in the presence of an enzyme the reaction follows a different path (in fact a different reaction occurs), for example:

In the absence of an enzyme:

• A+B = AB

In the presence of an enzyme:

• A+F = AF
• AF+B = AVF
• AVF = AB+F

where A, B are substrates, AB is the reaction product, F is the enzyme.

Enzymes cannot independently provide energy for endergonic reactions (which require energy to occur). Therefore, enzymes that carry out such reactions couple them with exergonic reactions that release more energy. For example, the synthesis reactions of biopolymers are often coupled with the ATP hydrolysis reaction.

The active centers of some enzymes are characterized by the phenomenon of cooperativity.

Specificity

Enzymes generally exhibit high specificity for their substrates (substrate specificity). This is achieved by partial complementarity between the shape, charge distribution and hydrophobic regions on the substrate molecule and the substrate binding site on the enzyme. Enzymes also typically exhibit high levels of stereospecificity (forming only one of the possible stereoisomers as a product or using only one stereoisomer as a substrate), regioselectivity (forming or breaking a chemical bond at only one of the possible positions of the substrate), and chemoselectivity (catalyzing only one chemical reaction from several possible for given conditions). Despite the overall high level of specificity, the degree of substrate and reaction specificity of enzymes may vary. For example, the endopeptidase trypsin only breaks the peptide bond after arginine or lysine unless they are followed by a proline, but pepsin is much less specific and can break the peptide bond following many amino acids.

Key-lock model

In 1890, Emil Fischer proposed that the specificity of enzymes is determined by the exact match between the shape of the enzyme and the substrate. This assumption is called the key-lock model. The enzyme combines with the substrate to form a short-lived enzyme-substrate complex. At the same time, despite the fact that this model explains the high specificity of enzymes, it does not explain the phenomenon of stabilization of the transition state, which is observed in practice.

Induced correspondence model

In 1958, Daniel Koshland proposed a modification of the “key-lock” model. Enzymes are generally not rigid, but flexible molecules. The active site of an enzyme can change conformation after binding a substrate. The side groups of the amino acids of the active site take a position that allows the enzyme to perform its catalytic function. In some cases, the substrate molecule also changes conformation after binding at the active site. Unlike the key-lock model, the induced-fit model explains not only the specificity of enzymes, but also the stabilization of the transition state. This model is called the “glove hand”.

Modifications

Many enzymes undergo modifications after the synthesis of the protein chain, without which the enzyme does not fully exhibit its activity. Such modifications are called post-translational modifications (processing). One of the most common types of modification is the addition of chemical groups to side residues of the polypeptide chain. For example, the addition of a phosphoric acid residue is called phosphorylation and is catalyzed by the enzyme kinase. Many eukaryotic enzymes are glycosylated, that is, modified by oligomers of carbohydrate nature.

Another common type of post-translational modification is cleavage of the polypeptide chain. For example, chymotrypsin (a protease involved in digestion) is obtained by cleaving a polypeptide region from chymotrypsinogen. Chymotrypsinogen is an inactive precursor of chymotrypsin and is synthesized in the pancreas. The inactive form is transported to the stomach, where it is converted into chymotrypsin. This mechanism is necessary in order to avoid the splitting of the pancreas and other tissues before the enzyme enters the stomach. The inactive enzyme precursor is also called a "zymogen".

Enzyme cofactors

Some enzymes perform the catalytic function on their own, without any additional components. However, there are enzymes that require non-protein components to carry out catalysis. Cofactors can be either inorganic molecules (metal ions, iron-sulfur clusters, etc.) or organic (for example, flavin or heme). Organic cofactors that are tightly bound to an enzyme are also called prosthetic groups. Organic cofactors that can be separated from the enzyme are called coenzymes.

An enzyme that requires the presence of a cofactor for catalytic activity, but is not bound to it, is called an apo enzyme. An apo enzyme in combination with a cofactor is called a holo enzyme. Most of the cofactors are associated with the enzyme by non-covalent, but rather strong interactions. There are also prosthetic groups that are covalently bound to the enzyme, for example, thiamine pyrophosphate in pyruvate dehydrogenase.

Regulation of enzymes

Some enzymes have small molecule binding sites and may be substrates or products of the metabolic pathway in which the enzyme enters. They decrease or increase the activity of the enzyme, which creates the opportunity for feedback.

Inhibition by end product

Metabolic pathway is a chain of sequential enzymatic reactions. Often the end product of a metabolic pathway is an inhibitor of an enzyme that accelerates the first reaction in that metabolic pathway. If there is too much of the final product, then it acts as an inhibitor for the very first enzyme, and if after this there is too little of the final product, then the first enzyme is activated again. Thus, inhibition by the final product according to the principle of negative feedback is an important way of maintaining homeostasis (relative constancy of the conditions of the internal environment of the body).

Influence of environmental conditions on enzyme activity

The activity of enzymes depends on the conditions in the cell or body - pressure, acidity of the environment, temperature, concentration of dissolved salts (ionic strength of the solution), etc.

Enzymes and vitamins

The role of biological molecules that make up the body.

Lecture No. 7

(2 hours)

General characteristics of enzymes

The structure of enzymes

Main stages of enzymatic catalysis

Properties of enzymes

Nomenclature and classification of enzymes

Enzyme inhibitors and activators

Classification of vitamins

Fat-soluble vitamins

Water soluble vitamins

B vitamins

General characteristics of enzymes and inorganic catalysts:

Only energetically possible reactions are catalyzed.

Does not change the direction of the reaction

Are not consumed during the reaction process,

They do not participate in the formation of reaction products.

Enzyme differences from non-biological catalysts:

Protein structure;

High sensitivity to physical and chemical environmental factors, work in milder conditions (atmospheric P, 30-40 o C, pH close to neutral);

High sensitivity to chemical reagents;

High efficiency (can accelerate the reaction by 10 8 -10 12 times; one molecule of F can catalyze 1000-1000000 molecules of substrate in 1 min);

High selectivity of F to substrates (substrate specificity) and to the type of reaction catalyzed (specificity of action);

F activity is regulated by special mechanisms.

According to their structure, enzymes are divided into simple(one-component) and complex(two-component). Simple consists only of the protein part, complex ( holoenzyme) - from protein and non-protein parts. Protein part - apoenzyme, non-protein - coenzyme(vitamins B1, B2, B5, B6, H, Q, etc.). Separately, apoenzyme and coenzyme do not have catalytic activity. The area on the surface of an enzyme molecule that interacts with a substrate molecule - active center.

Active center formed from amino acid residues located in various parts of the polypeptide chain or various close polypeptide chains. It is formed at the level of the tertiary structure of the enzyme protein. Within its boundaries, a substrate (adsorption) center and a catalytic center are distinguished. In addition to the active center, there are special functional areas - allosteric (regulatory) centers.

Catalytic center- this is the region of the active center of the enzyme, which is directly involved in the chemical transformations of the substrate. CC of simple enzymes is a combination of several amino acid residues located in different places in the polypeptide chain of the enzyme, but spatially close to each other due to the bends of this chain (serine, cysteine, tyrosine, histidine, arginine, asp. and glut. acids). The CC of a complex protein is more complex, because The prosthetic group of the enzyme is involved - coenzyme (water-soluble vitamins and fat-soluble vitamin K).

Substrate (adsorption) cent p is the site of the active center of the enzyme where sorption (binding) of the substrate molecule occurs. SC is formed by one, two, more often three amino acid radicals, which are usually located near the catalytic center. The main function of the SC is the binding of a substrate molecule and its transfer to the catalytic center in the most convenient position for it.

Allosteric center(“having a different spatial structure”) - a section of an enzyme molecule outside its active center that reversibly binds to any substance. This binding leads to a change in the conformation of the enzyme molecule and its activity. The active center either begins to work faster or slower. Accordingly, such substances are called allosteric activators or allosteric inhibitors.

Allosteric centers not found in all enzymes. They are present in enzymes, the work of which changes under the influence of hormones, mediators and other biologically active substances.

Enzymes (enzymes): importance for health, classification, application. Plant (food) enzymes: sources, benefits.

Enzymes (enzymes) are high-molecular substances of protein nature that perform the functions of catalysts in the body (they activate and accelerate various biochemical reactions). Fermentum translated from Latin means fermentation. The word enzyme has Greek roots: “en” - inside, “zyme” - leaven. These two terms, enzymes and enzymes, are used interchangeably, and the science of enzymes is called enzymology.

The importance of enzymes for health. Application of enzymes

Enzymes are called the keys to life for a reason. They have the unique property of acting specifically, selectively, only on a narrow range of substances. Enzymes cannot replace each other.

To date, more than 3 thousand enzymes have been known. Each cell of a living organism contains hundreds of different enzymes. Without them, not only is it impossible to digest food and convert it into substances that cells can absorb. Enzymes take part in the processes of renewal of skin, blood, bones, regulation of metabolism, cleansing of the body, wound healing, visual and auditory perception, the functioning of the central nervous system, and the implementation of genetic information. Breathing, muscle contraction, heart function, cell growth and division - all these processes are supported by the uninterrupted operation of enzyme systems.

Enzymes play an extremely important role in supporting our immunity. Specialized enzymes are involved in the production of antibodies necessary to fight viruses and bacteria, and activate the work of macrophages - large predatory cells that recognize and neutralize any foreign particles that enter the body. Removing cell waste products, neutralizing poisons, protecting against infection - all these are the functions of enzymes.

Special enzymes (bacteria, yeast, rennet enzymes) play an important role in the production of pickled vegetables, fermented milk products, dough fermentation, and cheese making.

Classification of enzymes

According to the principle of action, all enzymes (according to the international hierarchical classification) are divided into 6 classes:

1. Oxidoreductases – catalase, alcohol dehydrogenase, lactate dehydrogenase, polyphenol oxidase, etc.;
2. Transferases (transfer enzymes) – aminotransferases, acyltransferases, phosphorustransferases, etc.;
3. Hydrolases – amylase, pepsin, trypsin, pectinase, lactase, maltase, lipoprotein lipase, etc.;
4. Lyases;
5. Isomerases;
6. Ligases (synthetases) – DNA polymerase, etc.

Each class consists of subclasses, and each subclass consists of groups.

All enzymes can be divided into 3 large groups:

1. Digestive - act in the gastrointestinal tract, responsible for the processing of nutrients and their absorption into the systemic bloodstream. Enzymes that are secreted by the walls of the small intestine and the pancreas are called pancreatic;
2. Food (plant) – come (should come) with food. Foods that contain food enzymes are sometimes called live food;
3. Metabolic - trigger metabolic processes inside cells. Each system of the human body has its own network of enzymes.

Digestive enzymes, in turn, are divided into 3 categories:

1. Amylases – salivary amylase, pancreatic juice lactase, salivary maltase. These enzymes are present in both saliva and the intestines. They act on carbohydrates: the latter break down into simple sugars and easily penetrate into the blood;
2. Proteases are produced by the pancreas and gastric mucosa. They help digest proteins and also normalize the microflora of the digestive tract. Present in the intestines and gastric juice. Proteases include gastric pepsin and chymosin, erepsin in sparrow juice, pancreatic carboxypeptidase, chymotrypsin, trypsin;
3. Lipase – produced by the pancreas. Present in gastric juice. Helps break down and absorb fats.

Action of enzymes

The optimal temperature for enzyme activity is about 37 degrees, that is, body temperature. Enzymes have enormous power: they make seeds germinate and fats “burn.” On the other hand, they are extremely sensitive: at temperatures above 42 degrees, enzymes begin to break down. Both culinary processing of food and deep freezing lead to the death of enzymes and loss of their vitality. In canned, sterilized, pasteurized and even frozen foods, enzymes are partially or completely destroyed. But not only dead food, but also too cold and hot dishes kill enzymes. When we eat food that is too hot, we kill digestive enzymes and burn the esophagus. The stomach greatly increases in size, and then, due to spasms of the muscles that hold it, it becomes like a cockscomb. As a result, food enters the duodenum in an unprocessed state. If this happens constantly, problems such as dysbiosis, constipation, intestinal upset, and stomach ulcers may appear. The stomach also suffers from cold foods (ice cream, for example) - first it shrinks, and then increases in size, and the enzymes freeze. The ice cream begins to ferment, gases are released and the person gets bloated.

Digestive enzymes

It's no secret that good digestion is an essential condition for a full life and active longevity. Digestive enzymes play a crucial role in this process. They are responsible for the digestion, adsorption and assimilation of food, building our body like workers at a construction site. We can have all the building materials - minerals, proteins, fats, water, vitamins, but without enzymes, as without workers, construction will not advance a single step.

Modern man consumes too much food, for the digestion of which there are practically no enzymes in the body, for example, starchy foods - pasta, baked goods, potatoes.

If you eat a fresh apple, it will be digested by its own enzymes, and the effect of the latter is visible to the naked eye: the darkening of a bitten apple is the work of enzymes that are trying to heal the “wound” and protect the body from the threat of mold and bacteria. But if you bake an apple, in order to digest it, the body will have to use its own enzymes for digestion, since cooked food lacks natural enzymes. In addition, we lose forever those enzymes that “dead” foods take from our body, since their reserves in our body are not unlimited.

Plant (food) enzymes

Eating foods rich in enzymes not only facilitates digestion, but also releases energy that the body can use to cleanse the liver, patch holes in the immune system, rejuvenate cells, protect against tumors, etc. At the same time, a person feels light in his stomach, feels cheerful, and looks good. And raw plant fiber, which enters the body with live food, is required to feed microorganisms that produce metabolic enzymes.

Plant enzymes give us life and energy. If you plant two nuts in the ground - one roasted, and the other raw, soaked in water, then the roasted one will simply rot in the ground, and vitality will awaken in the raw grain in the spring, because it contains enzymes. And it is quite possible that a large lush tree will grow from it. Likewise, a person, consuming food that contains enzymes, receives life along with it. Enzyme-deprived foods cause our cells to work without rest, become overloaded, age and die. If there are not enough enzymes, “waste” begins to accumulate in the body: poisons, toxins, dead cells. This leads to weight gain, disease and early aging. A curious and at the same time sad fact: in the blood of elderly people, the content of enzymes is approximately 100 times lower than in young people.

Enzymes in products. Sources of plant enzymes

Sources of food enzymes are plant products from the garden, garden, and ocean. These are mainly vegetables, fruits, berries, herbs, and grains. Bananas, mangoes, papaya, pineapples, avocados, aspergillus plant, and sprouted grains contain their own enzymes. Plant enzymes are present only in raw, live foods.

Wheat sprouts are a source of amylase (which breaks down carbohydrates), papaya fruits contain proteases, and papaya and pineapple fruits contain peptidases. Sources of lipase (which breaks down fats) are fruits, seeds, rhizomes, tubers of cereal crops, mustard and sunflower seeds, and legume seeds. Bananas, pineapples, kiwi, papaya, and mango are rich in papain (which breaks down proteins). The source of lactase (an enzyme that breaks down milk sugar) is barley malt.

Advantages of plant (food) enzymes over animal (pancreatic) enzymes

Plant enzymes begin to process food already in the stomach, but pancreatic enzymes cannot work in the acidic gastric environment. When food enters the small intestine, plant enzymes will pre-digest it, reducing stress on the intestines and allowing nutrients to be better absorbed. In addition, plant enzymes continue their work in the intestines.

How to eat so that the body has enough enzymes?

Everything is very simple. Breakfast should consist of fresh berries and fruits (plus protein dishes - cottage cheese, nuts, sour cream). Every meal should start with vegetable salads with herbs. It is advisable that one meal every day includes only raw fruits, berries and vegetables. Dinner should be light - consist of vegetables (with a piece of chicken breast, boiled fish or a portion of seafood). Several times a month it is useful to have fasting days on fruits or freshly squeezed juices.

For high-quality digestion of food and full health, enzymes are simply irreplaceable. Excess weight, allergies, various gastrointestinal diseases - all these and many other problems can be overcome with a healthy diet. And the role of enzymes in nutrition is enormous. Our task is simply to make sure that they are present in our dishes every day and in sufficient quantities. Good health to you!