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

Enzymes are a special type of proteins, which by nature play the role of catalysts for various chemical processes.

This term is constantly heard, however, not everyone understands what an enzyme or enzyme is, what functions this substance performs, and also how enzymes differ from enzymes and whether they differ at all. We will find out all this now.

Without these substances, neither people nor animals would be able to digest food. And for the first time, humanity resorted to using enzymes in everyday life more than 5 thousand years ago, when our ancestors learned to store milk in “vessels” from the stomachs of animals. Under such conditions, under the influence of rennet, milk turned into cheese. And this is just one example of how an enzyme works as a catalyst that accelerates biological processes. Today, enzymes are indispensable in industry, they are important for the production of sugar, margarines, yoghurts, beer, leather, textiles, alcohol and even concrete. Detergents and washing powders also contain these useful substances - they help remove stains at low temperatures.

History of discovery

Enzyme translated from Greek means “leaven”. And humanity owes the discovery of this substance to the Dutchman Jan Baptist Van Helmont, who lived in the 16th century. At one time, he became very interested in alcoholic fermentation and during the course of his research he found an unknown substance that accelerates this process. The Dutchman called it fermentum, which means “fermentation.” Then, almost three centuries later, the Frenchman Louis Pasteur, also observing fermentation processes, came to the conclusion that enzymes are nothing more than substances of a living cell. And after some time, the German Eduard Buchner extracted an enzyme from yeast and determined that this substance was not a living organism. He also gave it his name - “zimaza”. A few years later, another German, Willi Kühne, proposed that all protein catalysts be divided into two groups: enzymes and enzymes. Moreover, he proposed to call the second term “sourdough”, the actions of which extend beyond living organisms. And only 1897 put an end to all scientific disputes: it was decided to use both terms (enzyme and enzyme) as absolute synonyms.

Structure: chain of thousands of amino acids

All enzymes are proteins, but not all proteins are enzymes. Like other proteins, enzymes are composed of. And what’s interesting is that the creation of each enzyme takes from one hundred to a million amino acids, strung like pearls on a thread. But this thread is never straight - it is usually curved hundreds of times. This creates a three-dimensional structure unique to each enzyme. Meanwhile, the enzyme molecule is a relatively large formation, and only a small part of its structure, the so-called active center, is involved in biochemical reactions.

Each amino acid is connected to another by a specific type of chemical bond, and each enzyme has its own unique sequence of amino acids. To create most of them, approximately 20 types of amino substances are used. Even minor changes in the amino acid sequence can dramatically change the appearance and “talents” of an enzyme.

Biochemical properties

Although a huge number of reactions occur in nature with the participation of enzymes, they can all be grouped into 6 categories. Accordingly, each of these six reactions occurs under the influence of a specific type of enzyme.

Reactions involving enzymes:

1. Oxidation and reduction.

The enzymes involved in these reactions are called oxidoreductases. As an example, we can recall how alcohol dehydrogenases convert primary alcohols to aldehyde.

1. Group transfer reaction.

The enzymes that enable these reactions to occur are called transferases. They have the ability to move functional groups from one molecule to another. This occurs, for example, when alanine aminotransferases transfer alpha amino groups between alanine and aspartate. Transferases also move phosphate groups between ATP and other compounds, and create disaccharides from glucose residues.

1. Hydrolysis.

The hydrolases involved in the reaction are able to break single bonds by adding water elements.

1. Creation or removal of a double bond.

This type of reaction occurs non-hydrolytically with the participation of lyase.

1. Isomerization of functional groups.

In many chemical reactions, the position of a functional group changes within the molecule, but the molecule itself consists of the same number and types of atoms as it was before the reaction began. In other words, the substrate and the reaction product are isomers. This type of transformation is possible under the influence of isomerase enzymes.

1. Formation of a single bond with elimination of the element water.

Hydrolases break the bond by adding water elements to the molecule. Lyases carry out the reverse reaction, removing the aqueous part from the functional groups. In this way, a simple connection is created.

How they work in the body

Enzymes speed up almost all chemical reactions that occur in cells. They are vital for humans, facilitating digestion and speeding up metabolism.

Some of these substances help break down overly large molecules into smaller “chunks” that the body can digest. Others, on the contrary, bind small molecules. But enzymes, scientifically speaking, are highly selective. This means that each of these substances is capable of accelerating only a certain reaction. The molecules that enzymes “work” with are called substrates. The substrates in turn create a bond with a part of the enzyme called the active site.

There are two principles that explain the specificity of the interaction between enzymes and substrates. In the so-called “key-lock” model, the active center of the enzyme occupies a strictly defined position in the substrate. According to another model, both participants in the reaction, the active site and the substrate, change their shapes to combine.

Regardless of the principle of interaction, the result is always the same - the reaction under the influence of the enzyme proceeds many times faster. As a result of this interaction, new molecules are “born”, which are then separated from the enzyme. And the catalyst substance continues to perform its work, but with the participation of other particles.

Hyper- and hypoactivity

There are times when enzymes perform their functions at the wrong intensity. Excessive activity causes excessive reaction product formation and substrate deficiency. The result is deterioration in health and serious illness. The cause of enzyme hyperactivity can be either a genetic disorder or an excess of vitamins or vitamins used in the reaction.

Enzyme underactivity can even cause death when, for example, enzymes do not remove toxins from the body or ATP deficiency occurs. The cause of this condition can also be mutated genes or, conversely, hypovitaminosis and deficiency of other nutrients. In addition, lower body temperature similarly slows down the functioning of enzymes.

Catalyst and more

Today you can often hear about the benefits of enzymes. But what are these substances on which the performance of our body depends?

Enzymes are biological molecules whose life cycle is not defined by birth and death. They simply work in the body until they dissolve. As a rule, this occurs under the influence of other enzymes.

During the biochemical reaction they do not become part of the final product. When the reaction is complete, the enzyme leaves the substrate. After this, the substance is ready to start working again, but on a different molecule. And this continues as long as the body needs.

The uniqueness of enzymes is that each of them performs only one assigned function. A biological reaction occurs only when the enzyme finds the correct substrate for it. This interaction can be compared to the principle of operation of a key and a lock - only correctly selected elements can “work together.” Another feature: they can work at low temperatures and moderate pH, and as catalysts they are more stable than any other chemicals.

Enzymes act as catalysts to speed up metabolic processes and other reactions.

Typically, these processes consist of specific steps, each of which requires the work of a specific enzyme. Without this, the conversion or acceleration cycle will not be able to complete.

Perhaps the best known of all the functions of enzymes is that of a catalyst. This means that enzymes combine chemical reagents in such a way as to reduce the energy costs required to form a product more quickly. Without these substances, chemical reactions would proceed hundreds of times slower. But the abilities of enzymes do not end there. All living organisms contain the energy they need to continue living. Adenosine triphosphate, or ATP, is a kind of charged battery that supplies cells with energy. But the functioning of ATP is impossible without enzymes. And the main enzyme that produces ATP is synthase. For every molecule of glucose that is converted into energy, the synthase produces about 32-34 molecules of ATP.

In addition, enzymes (lipase, amylase, protease) are actively used in medicine. In particular, they serve as a component of enzymatic preparations such as Festal, Mezim, Panzinorm, Pancreatin, used to treat indigestion. But some enzymes can also influence the circulatory system (dissolve blood clots) and accelerate the healing of purulent wounds. And even in anti-cancer therapy they also resort to the help of enzymes.

Factors determining enzyme activity

Since the enzyme is capable of accelerating reactions many times, its activity is determined by the so-called turnover number. This term refers to the number of molecules of substrate (reacting substance) that 1 molecule of enzyme can transform in 1 minute. However, there are a number of factors that determine the speed of the reaction:

1. Substrate concentration.

Increasing the substrate concentration leads to an acceleration of the reaction. The more molecules of the active substance, the faster the reaction occurs, since more active centers are involved. However, acceleration is possible only until all enzyme molecules are used. After this, even increasing the substrate concentration will not speed up the reaction.

1. Temperature.

Typically, increasing the temperature speeds up reactions. This rule works for most enzymatic reactions, as long as the temperature does not rise above 40 degrees Celsius. After this mark, the reaction rate, on the contrary, begins to decrease sharply. If the temperature drops below a critical level, the rate of enzymatic reactions will increase again. If the temperature continues to rise, the covalent bonds break down and the catalytic activity of the enzyme is lost forever.

1. Acidity.

The rate of enzymatic reactions is also affected by pH. Each enzyme has its own optimal acidity level at which the reaction occurs most adequately. Changing the pH level affects the activity of the enzyme, and therefore the speed of the reaction. If the changes are too great, the substrate loses its ability to bind to the active nucleus and the enzyme can no longer catalyze the reaction. With the restoration of the required pH level, enzyme activity is also restored.

Enzymes present in the human body can be divided into 2 groups:

• metabolic;
• digestive.

Metabolic “work” to neutralize toxic substances, and also contribute to the production of energy and proteins. And, of course, they accelerate biochemical processes in the body.

What the digestive organs are responsible for is clear from the name. But here, too, the principle of selectivity comes into play: a certain type of enzyme affects only one type of food. Therefore, to improve digestion, you can resort to a little trick. If the body does not digest something from food well, then it is necessary to supplement the diet with a product containing an enzyme that can break down difficult-to-digest food.

Food enzymes are catalysts that break down food to a state in which the body is able to absorb useful substances from them. Digestive enzymes come in several types. In the human body, different types of enzymes are found in different parts of the digestive tract.

Oral cavity

At this stage, the food is exposed to alpha-amylase. It breaks down carbohydrates, starches and glucose found in potatoes, fruits, vegetables and other foods.

Stomach

Here pepsin breaks down proteins into peptides, and gelatinase breaks down gelatin and collagen contained in meat.

Pancreas

At this stage they “work”:

• trypsin – responsible for the breakdown of proteins;
• alpha-chymotrypsin - helps digest proteins;
• elastases - break down some types of proteins;
• Nucleases – help break down nucleic acids;
• Steapsin – promotes the absorption of fatty foods;
• amylase – responsible for the absorption of starches;
• lipase – breaks down fats (lipids) found in dairy products, nuts, oils and meat.

Small intestine

They “conjure” food particles:

• peptidases – break down peptide compounds to the level of amino acids;
• sucrase – helps digest complex sugars and starches;
• maltase – breaks down disaccharides into monosaccharides (malt sugar);
• lactase – breaks down lactose (glucose found in dairy products);
• lipase – promotes the absorption of triglycerides and fatty acids;
• Erepsin – affects proteins;
• isomaltase – “works” with maltose and isomaltose.

Colon

Here the functions of enzymes are performed by:

• Escherichia coli – responsible for digesting lactose;
• lactobacilli - affect lactose and some other carbohydrates.

In addition to the enzymes mentioned above, there are also:

• diastase – digests plant starch;
• invertase – breaks down sucrose (table sugar);
• glucoamylase - converts starch into glucose;
• alpha-galactosidase – promotes the digestion of beans, seeds, soy products, root and leafy vegetables;
• bromelain - an enzyme obtained from, promotes the breakdown of various types of proteins, is effective at different levels of environmental acidity, and has anti-inflammatory properties;
• Papain is an enzyme isolated from raw papaya that promotes the breakdown of small and large proteins and is effective in a wide range of substrates and acidities.
• cellulase – breaks down cellulose, plant fibers (not found in the human body);
• endoprotease – breaks down peptide bonds;
• ox bile extract – an enzyme of animal origin, stimulates intestinal motility;
and other minerals;
• xylanase – breaks down glucose from grains.

Catalysts in products

Enzymes are critical to health because they help the body break down food components into a usable state for the nutrients. The intestines and pancreas produce a wide range of enzymes. But besides this, many of their beneficial substances that promote digestion are also found in some foods.

Fermented foods are an almost ideal source of beneficial bacteria necessary for proper digestion. And while pharmaceutical probiotics “work” only in the upper part of the digestive system and often do not reach the intestines, the effect of enzymatic products is felt throughout the gastrointestinal tract.

For example, apricots contain a mixture of beneficial enzymes, including invertase, which is responsible for the breakdown of glucose and promotes the rapid release of energy.

Avocado can serve as a natural source of lipase (promotes faster digestion of lipids). In the body, this substance is produced by the pancreas. But in order to make life easier for this organ, you can treat yourself, for example, to a salad with avocado - tasty and healthy.

In addition to being perhaps the best-known source of potassium, bananas also supply amylase and maltase to the body. Amylase is also found in bread, potatoes, and cereals. Maltase helps break down maltose, the so-called malt sugar that is found in abundance in beer and corn syrup.

Another exotic fruit, pineapple contains a whole set of enzymes, including bromelain. And it, according to some studies, also has anti-cancer and anti-inflammatory properties.

Extremophiles and industry

Extremophiles are substances that are able to maintain vital functions in extreme conditions.

Living organisms, as well as the enzymes that allow them to function, have been found in geysers where the temperature is close to the boiling point, and deep in ice, as well as in conditions of extreme salinity (Death Valley in the USA). In addition, scientists have found enzymes for which the pH level, as it turns out, is also not a fundamental requirement for effective operation. Researchers are studying extremophile enzymes with particular interest as substances that can be widely used in industry. Although today enzymes have already found their use in industry as biologically and environmentally friendly substances. Enzymes are used in the food industry, cosmetology, and the production of household chemicals.

Moreover, the “services” of enzymes in such cases are cheaper than synthetic analogues. In addition, natural substances are biodegradable, which makes their use environmentally friendly. In nature, there are microorganisms that can break down enzymes into individual amino acids, which then become components of a new biological chain. But that, as they say, is a completely different story.

Millions of chemical reactions take place in the cell of any living organism. Each of them is of great importance, so it is important to maintain the speed of biological processes at a high level. Almost every reaction is catalyzed by its own enzyme. What are enzymes? What is their role in the cell?

Enzymes. Definition

The term "enzyme" comes from the Latin fermentum - leaven. They can also be called enzymes from the Greek en zyme - “in yeast”.

Enzymes are biologically active substances, so any reaction occurring in a cell cannot occur without their participation. These substances act as catalysts. Accordingly, any enzyme has two main properties:

1) The enzyme accelerates the biochemical reaction, but is not consumed.

2) The value of the equilibrium constant does not change, but only accelerates the achievement of this value.

Enzymes speed up biochemical reactions a thousand, and in some cases a million, times. This means that in the absence of the enzymatic apparatus, all intracellular processes will practically stop, and the cell itself will die. Therefore, the role of enzymes as biologically active substances is great.

The variety of enzymes allows for versatile regulation of cell metabolism. Many enzymes of different classes take part in any reaction cascade. Biological catalysts are highly selective due to the specific conformation of the molecule. Since enzymes in most cases are of a protein nature, they are located in a tertiary or quaternary structure. This is again explained by the specificity of the molecule.

Functions of enzymes in the cell

The main task of the enzyme is to accelerate the corresponding reaction. Any cascade of processes, from the decomposition of hydrogen peroxide to glycolysis, requires the presence of a biological catalyst.

The correct functioning of enzymes is achieved by high specificity to a specific substrate. This means that a catalyst can only accelerate a certain reaction and no other, even very similar ones. According to the degree of specificity, the following groups of enzymes are distinguished:

1) Enzymes with absolute specificity, when only one single reaction is catalyzed. For example, collagenase breaks down collagen, and maltase breaks down maltose.

2) Enzymes with relative specificity. This includes substances that can catalyze a certain class of reactions, for example, hydrolytic cleavage.

The work of a biocatalyst begins from the moment its active center attaches to the substrate. In this case, they talk about complementary interaction like a lock and key. Here we mean the complete coincidence of the shape of the active center with the substrate, which makes it possible to accelerate the reaction.

The next stage is the reaction itself. Its speed increases due to the action of an enzymatic complex. Ultimately, we get an enzyme that is associated with the reaction products.

The final stage is the detachment of the reaction products from the enzyme, after which the active center again becomes free for the next job.

Schematically, the work of the enzyme at each stage can be written as follows:

1) S + E ——> SE

2) SE ——> SP

3) SP ——> S + P, where S is the substrate, E is the enzyme, and P is the product.

Classification of enzymes

A huge number of enzymes can be found in the human body. All knowledge about their functions and operation was systematized, and as a result, a single classification emerged, thanks to which you can easily determine what a particular catalyst is intended for. The 6 main classes of enzymes are presented here, as well as examples of some of the subgroups.

1. Oxidoreductases.

Enzymes of this class catalyze redox reactions. A total of 17 subgroups are distinguished. Oxidoreductases usually have a non-protein part, represented by a vitamin or heme.

Among the oxidoreductases, the following subgroups are often found:

a) Dehydrogenases. The biochemistry of dehydrogenase enzymes involves the removal of hydrogen atoms and their transfer to another substrate. This subgroup is most often found in the reactions of respiration and photosynthesis. Dehydrogenases necessarily contain a coenzyme in the form of NAD/NADP or flavoproteins FAD/FMN. Metal ions are often found. Examples include enzymes such as cytochrome reductase, pyruvate dehydrogenase, isocitrate dehydrogenase, as well as many liver enzymes (lactate dehydrogenase, glutamate dehydrogenase, etc.).

b) Oxidases. A number of enzymes catalyze the addition of oxygen to hydrogen, as a result of which the reaction products can be water or hydrogen peroxide (H 2 0, H 2 0 2). Examples of enzymes: cytochrome oxidase, tyrosinase.

c) Peroxidases and catalases are enzymes that catalyze the decomposition of H 2 O 2 into oxygen and water.

d) Oxygenases. These biocatalysts accelerate the addition of oxygen to the substrate. Dopamine hydroxylase is one example of such enzymes.

2. Transferases.

The task of enzymes of this group is to transfer radicals from a donor substance to a recipient substance.

a) Methyltransferases. DNA methyltransferases are the main enzymes that control the process of nucleotide replication and play a large role in regulating the functioning of nucleic acids.

b) Acyltransferases. Enzymes of this subgroup transport an acyl group from one molecule to another. Examples of acyltransferases: lecithin cholesterol acyltransferase (transfers a functional group from a fatty acid to cholesterol), lysophosphatidylcholine acyltransferase (transfers an acyl group to lysophosphatidylcholine).

c) Aminotransferases are enzymes that are involved in the conversion of amino acids. Examples of enzymes: alanine aminotransferase, which catalyzes the synthesis of alanine from pyruvate and glutamate by amino group transfer.

d) Phosphotransferases. Enzymes of this subgroup catalyze the addition of a phosphate group. Another name for phosphotransferases, kinases, is much more common. Examples include enzymes such as hexokinases and aspartate kinases, which add phosphorus residues to hexoses (most often glucose) and aspartic acid, respectively.

3. Hydrolases - a class of enzymes that catalyze the cleavage of bonds in a molecule with the subsequent addition of water. Substances that belong to this group are the main digestive enzymes.

a) Esterases - break ether bonds. An example is lipases, which break down fats.

b) Glycosidases. The biochemistry of enzymes of this series consists in the destruction of glycosidic bonds of polymers (polysaccharides and oligosaccharides). Examples: amylase, sucrase, maltase.

c) Peptidases are enzymes that catalyze the breakdown of proteins into amino acids. Peptidases include enzymes such as pepsins, trypsin, chymotrypsin, and carboxypeptidase.

d) Amidases - cleave amide bonds. Examples: arginase, urease, glutaminase, etc. Many amidase enzymes are found in

4. Lyases are enzymes that are similar in function to hydrolases, but the cleavage of bonds in molecules does not require water. Enzymes of this class always contain a non-protein part, for example, in the form of vitamins B1 or B6.

a) Decarboxylase. These enzymes act on the C-C bond. Examples include glutamate decarboxylase or pyruvate decarboxylase.

b) Hydratases and dehydratases are enzymes that catalyze the reaction of cleavage of C-O bonds.

c) Amidine lyases - destroy C-N bonds. Example: arginine succinate lyase.

d) P-O lyase. Such enzymes, as a rule, cleave a phosphate group from a substrate substance. Example: adenylate cyclase.

The biochemistry of enzymes is based on their structure

The abilities of each enzyme are determined by its individual, unique structure. Any enzyme is first and foremost a protein, and its structure and degree of folding play a decisive role in determining its function.

Each biocatalyst is characterized by the presence of an active center, which, in turn, is divided into several independent functional areas:

1) The catalytic center is a special region of the protein through which the enzyme attaches to the substrate. Depending on the conformation of the protein molecule, the catalytic center can take on a variety of shapes, which must fit the substrate just like a lock fits a key. This complex structure explains what is in the tertiary or quaternary state.

2) Adsorption center - acts as a “holder”. Here, first of all, the connection between the enzyme molecule and the substrate molecule occurs. However, the bonds formed by the adsorption center are very weak, which means that the catalytic reaction at this stage is reversible.

3) Allosteric centers can be located both in the active center and over the entire surface of the enzyme as a whole. Their function is to regulate the functioning of the enzyme. Regulation occurs with the help of inhibitor molecules and activator molecules.

Activator proteins, by binding to the enzyme molecule, speed up its work. Inhibitors, on the other hand, inhibit catalytic activity, and this can happen in two ways: either the molecule binds to an allosteric site in the region of the active site of the enzyme (competitive inhibition), or it attaches to another region of the protein (non-competitive inhibition). considered more effective. After all, this closes the place for the substrate to bind to the enzyme, and this process is possible only in the case of an almost complete coincidence of the shape of the inhibitor molecule and the active center.

An enzyme often consists not only of amino acids, but also of other organic and inorganic substances. Accordingly, apoenzyme is the protein part, coenzyme is the organic part, and cofactor is the inorganic part. The coenzyme can be represented by carbohydrates, fats, nucleic acids, and vitamins. In turn, a cofactor is most often auxiliary metal ions. The activity of enzymes is determined by its structure: additional substances included in the composition change the catalytic properties. Various types of enzymes are the result of a combination of all the listed factors in the formation of the complex.

Regulation of enzymes

Enzymes as biologically active substances are not always necessary for the body. The biochemistry of enzymes is such that they can, if catalyzed excessively, harm a living cell. To prevent the harmful effects of enzymes on the body, it is necessary to somehow regulate their work.

Since enzymes are protein in nature, they are easily destroyed at high temperatures. The denaturation process is reversible, but it can significantly affect the performance of substances.

pH also plays a big role in regulation. The highest enzyme activity is usually observed at neutral pH values ​​(7.0-7.2). There are also enzymes that work only in acidic environments or only in alkaline environments. Thus, a low pH is maintained in cellular lysosomes, at which the activity of hydrolytic enzymes is maximum. If they accidentally enter the cytoplasm, where the environment is already closer to neutral, their activity will decrease. This protection against “self-eating” is based on the peculiarities of the work of hydrolases.

It is worth mentioning the importance of coenzyme and cofactor in the composition of enzymes. The presence of vitamins or metal ions significantly affects the functioning of some specific enzymes.

Enzyme nomenclature

All enzymes in the body are usually named depending on their belonging to any of the classes, as well as on the substrate with which they react. Sometimes not one, but two substrates are used in the name.

Examples of the names of some enzymes:

1. Liver enzymes: lactate dehydrogenase, glutamate dehydrogenase.
2. Full systematic name of the enzyme: lactate-NAD+-oxidoreductase.

Trivial names that do not adhere to the rules of nomenclature have also been preserved. Examples are digestive enzymes: trypsin, chymotrypsin, pepsin.

Enzyme synthesis process

The functions of enzymes are determined at the genetic level. Since the molecule is, by and large, a protein, its synthesis exactly repeats the processes of transcription and translation.

Enzyme synthesis occurs according to the following scheme. First, information about the desired enzyme is read from DNA, resulting in the formation of mRNA. Messenger RNA encodes all the amino acids that make up the enzyme. Regulation of enzymes can also occur at the DNA level: if the product of the catalyzed reaction is sufficient, gene transcription stops and vice versa, if there is a need for the product, the transcription process is activated.

After the mRNA has entered the cytoplasm of the cell, the next stage begins - translation. On the ribosomes of the endoplasmic reticulum, the primary chain is synthesized, consisting of amino acids connected by peptide bonds. However, the protein molecule in the primary structure cannot yet perform its enzymatic functions.

The activity of enzymes depends on the structure of the protein. On the same EPS, protein twisting occurs, as a result of which first secondary and then tertiary structures are formed. The synthesis of some enzymes stops already at this stage, but to activate catalytic activity it is often necessary to add a coenzyme and a cofactor.

In certain areas of the endoplasmic reticulum, the organic components of the enzyme are added: monosaccharides, nucleic acids, fats, vitamins. Some enzymes cannot work without the presence of a coenzyme.

The cofactor plays a crucial role in the formation of Some enzyme functions are available only when the protein reaches a domain organization. Therefore, the presence of a quaternary structure, in which the connecting link between several protein globules is a metal ion, is very important for them.

Multiple Forms of Enzymes

There are situations when it is necessary to have several enzymes that catalyze the same reaction, but differ from each other in some parameters. For example, an enzyme can work at 20 degrees, but at 0 degrees it will no longer be able to perform its functions. What should a living organism do in such a situation at low ambient temperatures?

This problem is easily solved by the presence of several enzymes that catalyze the same reaction, but operate under different conditions. There are two types of multiple forms of enzymes:

1. Isoenzymes. Such proteins are encoded by different genes, consist of different amino acids, but catalyze the same reaction.
2. True plural forms. These proteins are transcribed from the same gene, but modification of the peptides occurs on the ribosomes. The output is several forms of the same enzyme.

As a result, the first type of multiple forms is formed at the genetic level, while the second type is formed at the post-translational level.

The importance of enzymes

In medicine, it comes down to the release of new medicines, which already contain substances in the required quantities. Scientists have not yet found a way to stimulate the synthesis of missing enzymes in the body, but today there are widespread drugs that can temporarily compensate for their deficiency.

Various enzymes in the cell catalyze a large number of reactions associated with maintaining life. One of these enisms are representatives of the group of nucleases: endonucleases and exonucleases. Their job is to maintain a constant level of nucleic acids in the cell and remove damaged DNA and RNA.

Don't forget about the phenomenon of blood clotting. As an effective protective measure, this process is controlled by a number of enzymes. The main one is thrombin, which converts the inactive protein fibrinogen into active fibrin. Its threads create a kind of network that clogs the site of damage to the vessel, thereby preventing excessive blood loss.

Enzymes are used in winemaking, brewing, and the production of many fermented milk products. Yeast can be used to produce alcohol from glucose, but an extract from it is sufficient for this process to proceed successfully.

Interesting facts you didn't know about

All enzymes in the body have a huge mass - from 5000 to 1,000,000 Da. This is due to the presence of protein in the molecule. For comparison: the molecular weight of glucose is 180 Da, and carbon dioxide is only 44 Da.

To date, more than 2000 enzymes have been discovered that have been found in the cells of various organisms. However, most of these substances have not yet been fully studied.

Enzyme activity is used to produce effective washing powders. Here, enzymes perform the same role as in the body: they break down organic matter, and this property helps in the fight against stains. It is recommended to use such washing powder at a temperature no higher than 50 degrees, otherwise denaturation may occur.

According to statistics, 20% of people around the world suffer from a deficiency of any of the enzymes.

The properties of enzymes were known for a very long time, but only in 1897 did people realize that not the yeast itself, but an extract from its cells, could be used to ferment sugar into alcohol.

Structure and mechanism of action of enzymes

Like all proteins, enzymes are synthesized as a linear chain of amino acids that folds in a specific 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.
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.
Since all enzymes are proteins (but not all proteins are enzymes), let us dwell in more detail on the structure of proteins

Proteins are complex high-molecular natural organic substances made from

amino acids , connected by peptide bonds. The sequence of amino acids in a protein is determined by the gene and encrypted in the genetic code. Although this genetic coding determines the 20 "standard" amino acids, their arrangement in the protein (protein) allows for the creation of countless different proteins. Proteins can work together to achieve a specific function, and they often bind to form a stabilized complex.

Model of 1,3-beta-D-glucanase from
crystal stalk
sea ​​mollusk Spisula sachalinensis

Protein molecules are linear polymers consisting of 20 basic L-α-amino acids (which are monomers) and, in some cases, modified basic amino acids (although modifications occur after protein synthesis at the ribosome). One- or three-letter abbreviations are used to designate amino acids in the scientific literature.

When a protein is formed as a result of the interaction of the α-amino group (-NH 2) of one amino acid with the α-carboxyl group (-COOH) of another amino acid, peptide bonds are formed. The ends of the protein are called the C- and N-terminus (depending on which of the terminal amino acid groups is free: -COOH or -NH 2, respectively). During protein synthesis on the ribosome, new amino acids are added to the C-terminus, so the name of the peptide or protein is given by listing the amino acid residues starting from the N-terminus.

Proteins with a length of 2 to 100 amino acid residues are often called peptides, and with a higher degree of polymerization - proteins, although this division is very arbitrary.

The sequence of amino acids in a protein corresponds to the information contained in the gene for that protein. This information is presented in the form of a sequence of nucleotides, with one amino acid corresponding to one or more sequences of three nucleotides - the so-called triplets or codons. Which amino acid corresponds to a given codon in mRNA is determined by the genetic code, which may differ slightly from organism to organism.

Homologous proteins (performing the same function and presumably having a common evolutionary origin, for example, hemoglobins) from different organisms have different amino acid residues at many places in the chain, called variable, as opposed to invariant, common residues. Based on the degree of homology, it is possible to estimate the evolutionary distance between taxa.

Simple and complex proteins

There are simple proteins (proteins) and complex proteins (proteids). Simple proteins contain only amino acids linked in a chain. Complex proteins also have non-amino acid groups. These additional groups within complex proteins are called “prosthetic groups.” Many eukaryotic proteins, for example, have polysaccharide chains that help the protein adopt the desired conformation and provide additional stability. Disulfide bridges also play a role as elements necessary for the protein to adopt the correct 3-dimensional shape, and are the main component of complex proteins. But it is important to note that basically only eukaryotes are capable of synthesizing complex proteins (proteins), since prokaryotes do not have enough compartmentalization to create additional changes present in complex proteins, and even if they can do this in the periplasmic space, this happens either rarely , or ineffective.

Levels of structural organization of proteins

In addition to the sequence (primary structure), the three-dimensional structure of the protein, which is formed during the process of folding (from the English folding, i.e. folding), is extremely important. It has been shown that despite the enormous size of the molecules, natural proteins have only one conformation; proteins that have lost their structure lose their properties.
There are four levels of protein structure:
. Primary structure— the sequence of amino acid residues in a polypeptide chain.

Secondary structure- local ordering of a fragment of a polypeptide chain, stabilized by hydrogen bonds and hydrophobic interactions. Below are some common types of protein secondary structure:
α-helices are dense turns around the long axis of the molecule, one turn consists of 4 amino acid residues, the helix is ​​stabilized by hydrogen bonds between H and O peptide groups, spaced 4 units apart. The helix can be constructed exclusively from one type of amino acid stereoisomer (L or D), although it can be either left-handed or right-handed; in proteins, right-handed is predominant. The helix is ​​disrupted by electrostatic interactions of glutamic acid, lysine, arginine, closely located asparagine, serine, threonine and leucine can sterically interfere with the formation of the helix, proline causes the chain to bend and also disrupts the α-helix.
β-sheets (folded layers) are several zigzag polypeptide chains in which hydrogen bonds are formed between different chains, and not within one, as is the case in an α-helix. These chains usually have their N-termini pointing in different directions (antiparallel orientation). For the formation of sheets, the small size of the R-groups of amino acids is important; glycine and alanine usually predominate.
unordered fragments. ъ

Tertiary structure
- spatial structure of the polypeptide chain - the relative arrangement of secondary structure elements, stabilized by the interaction between the side chains of amino acid residues. The following take part in stabilizing the tertiary structure:
covalent bonds (between two cysteines - disulfide bridges);
ionic (electrostatic) interactions (between oppositely charged amino acid residues);
hydrogen bonds;
hydrophobic interactions.

Quaternary structure
- subunit structure of the protein. The relative arrangement of several polypeptide chains as part of a single protein complex.

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.

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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.