Function of enzymes. The role of enzymes in the body

Enzymes are globular proteins that help all cellular processes to flow. Like all catalysts, they can not reverse the reaction, but serve to accelerate it.

Enzyme localization in the cell

Inside the cell, individual enzymes are usually contained and act in strictly defined organelles. The localization of enzymes is directly related to the function that this section of the cell usually performs.

Almost all enzymes of glycolysis are located in the cytoplasm. The enzymes of the tricarboxylic acid cycle are in the mitochondrial matrix. The active substances of hydrolysis are contained in lysosomes.

Individual tissues and organs of animals and plants differ not only in the set of enzymes, but also in their activity. This feature of the tissues is used in the clinic for the diagnosis of certain diseases.

There are also age features in the activity and the set of enzymes in the tissues. They are most clearly visible during embryonic development in tissue differentiation.

Nomenclature of enzymes

There are several systems of names, each of which takes into account the properties of enzymes to varying degrees.

• Trivial. The names of substances are given by random signs. For example, pepsin (pepsis - "digestion", Greek.) And trypsin (tripsis - "dilute", Greek).
• Rational. The name of the enzyme consists of the substrate and the end of the "-as". For example, amylase accelerates the hydrolysis of starch (amylo - "starch", Greek).
• Moscow. It was adopted in 1961 by the International Commission on the Nomenclature of Enzymes at the 5th International Biochemical Congress. The name of the substance is made up of a substrate and a reaction that is catalyzed (accelerated) by the enzyme. If the function of enzymes is to transfer a group of atoms from one molecule (substrate) to another (acceptor), the name of the catalyst includes the chemical name of the acceptor. For example, in the transfer of the amino group from alanine to 2-oxyglutaric acid, the enzyme alanine: 2-oxoglutarate aminotransferase participates. The title reflects:
• Substrate - alanine;
• Acceptor - 2-oxoglutaric acid;
• The reaction carries an amino group.

The International Commission compiled a list of all known enzymes, which is constantly being supplemented. This is due to the discovery of new substances.

Classification of enzymes

You can divide enzymes into groups in two ways. The first offers two classes of these substances:

• Simple - consist only of protein;
• Complex - contain the protein part (apoenzyme) and non-protein, called coenzyme.

The non-protein part of the complex enzyme can include vitamins. Interaction with other substances occurs through an active center. Whole molecule of the enzyme does not participate in the process.

The properties of enzymes, like other proteins, are determined by their structure. Depending on it, the catalysts accelerate only their reactions.

The second method of classification divides substances according to the function that enzymes perform. The result is six classes:

• Oxidoreductase;
• Transferase;
• Hydrolases;
• Isomerase;
• Lyases;
• Ligase.

These are generally accepted groups, they differ not only in the types of reactions that regulate their enzymes. The substances of different groups differ in structure. And the functions of enzymes in the cell, therefore, can not be the same.

Oxidoreductases - oxidation-reduction

The main function of the enzymes of the first group is the acceleration of oxidation-reduction reactions. A characteristic feature: the ability to form chains of oxidative enzymes in which electrons or hydrogen atoms are transported from the very first substrate to the final acceptor. These substances are divided according to the principle of work or the place of work in the reaction.

1. Aerobic dehydrogenases (oxidases) accelerate the transfer of electrons or protons directly to oxygen atoms. Anaerobic ones do the same actions, but in reactions that take place without transfer of electrons or hydrogen atoms to oxygen atoms.
2. Primary dehydrogenases catalyze the removal of hydrogen atoms from the oxidizable substance (primary substrate). Secondary - accelerate the removal of hydrogen atoms from the secondary substrate, they were obtained with the help of primary dehydrogenase.

Another feature: being two-component catalysts with a very limited set of coenzymes (active groups), they can accelerate many of the most diverse oxidation-reduction reactions. This is achieved by a large number of options: the same coenzyme can join different apoenzymes. In each case, a special oxidoreductase with its properties is obtained.

There is another function of the enzymes of this group, which can not be ignored - they accelerate the flow of chemical processes associated with the release of energy. Such reactions are called exothermic.

Transferases - carriers

These enzymes perform the function of accelerating the reactions of molecular residue transfer and functional groups. For example, phosphofructokinase.

There are eight groups of catalysts, based on the tolerable group. Let us consider only some of them.

1. Phosphotransferases - help to transport the residues of phosphoric acid. They are divided into subclasses in accordance with the destination (alcohol, carboxyl and others).
2. Aminotransferase - accelerate the reactions of amino acid renamination.
3. Glycosyltransferases - transfer glycosyl residues from molecules of phosphoric esters to molecules of mono- and polysaccharides. Provide the decomposition and synthesis of oligo- or polysaccharides in plants and animals. For example, they are involved in the decay of sucrose.
4. Acyltransferases transfer the residues of carboxylic acids to amines, alcohols and amino acids. Acyl-coenzyme-A is a universal source of acyl groups. It can be considered as an active group of acyltransferases. Most often, acyl acetic acid is transferred.

Hydrolases - cleaved with water

In this group, the enzymes act as catalysts for the cleavage reactions (less often the synthesis) of organic compounds in which water participates. Substances of this group are contained in cells and in digestive juice. Molecules of catalysts in the gastrointestinal tract consist of one component.

The site of localization of these enzymes is lysosomes. They perform the protective functions of enzymes in the cell: they break down foreign substances that have passed through the membrane. They also destroy those substances that are no longer needed by the cage, for which the lysosomes were nicknamed medical orderlies.

Another "nickname" is cellular suicide, as they are the main tool for autolysis of the cell. If an infection appeared, inflammatory processes began, the lysosome membrane becomes permeable and the hydrolases exit into the cytoplasm, destroying everything in their path and destroying the cell.

Separate several types of catalysts from this group:

• Esterases - are responsible for the hydrolysis of esters of alcohols;
• Glycosidase - accelerate the hydrolysis of glycosides, depending on which isomer they act on, secrete α- or β-glycosidases;
• Peptide hydrolases - are responsible for the hydrolysis of peptide bonds in proteins, and under certain conditions and for their synthesis, but this method of protein synthesis is not used in a living cell;
• Amidases - are responsible for the hydrolysis of acid amides, for example, urease catalyses the decomposition of urea to ammonia and water.

Isomerase - molecule transformation

These substances accelerate changes within a single molecule. They can be geometric or structural. This can happen in different ways:

• Transfer of hydrogen atoms;
• Movement of the phosphate group;
• Change in the arrangement of atomic groupings in space;
• Movement of the double bond.

Isomerization can be affected by organic acids, carbohydrates or amino acids. Isomerases can convert aldehydes into ketones and, conversely, the cis-form can be rearranged into a trans-form and vice versa. To better understand what function the enzymes of this group perform, it is necessary to know the differences in isomers.

Lies tear the connection

These enzymes accelerate non-hydrolytic decomposition of organic compounds along bonds:

• Carbon-carbon;
• Phosphorus-oxygen;
• Carbon-sulfur;
• Carbon-nitrogen;
• Carbon-oxygen.

In this case, such simple products as carbon dioxide, water, ammonia are isolated, and double bonds are closed. Few of these reactions can go in the opposite direction, the corresponding enzymes catalyze the processes of not only decay, but also synthesis, under suitable conditions.

Classification of lyases occurs according to the type of connection they break. They are complex enzymes.

Ligase crosslinked

The main function of the enzymes of this group is the acceleration of the synthesis reactions. Their feature - the conjugation of the creation with the disintegration of substances that are capable of giving energy for the realization of the biosynthetic process. There are six subclasses according to the type of communication formed. Five of them are identical to the subgroups of lyases, and the sixth is responsible for creating a "nitrogen-metal" bond.

Some ligases take part in especially important cell processes. For example, DNA ligase is involved in the replication of deoxyribonucleic acid. It sews single-strand breaks, creating new phosphodiester bonds. It is she who unites the fragments of Okaucasia.

The same enzyme is actively used in genetic engineering. It allows scientists to sew DNA molecules from the pieces they need, creating unique chains of deoxyribonucleic acid. They can lay any information, thus creating a factory for manufacturing the necessary proteins. For example, you can sew a piece of DNA into the DNA that is responsible for the synthesis of insulin. And when the cell will broadcast its own proteins, it at the same time will do the useful substance necessary for medical purposes. It can only be cleared, and it will help a lot of sick people.

Enormous role of enzymes in the body

They can increase the reaction rate by more than ten times. This is simply necessary for the normal functioning of the cell. And enzymes are involved in every reaction. Therefore, the functions of enzymes in the body are diverse, as are all the processes that are taking place. A disruption of the work of these catalysts leads to severe consequences.

Widely used enzymes in the food, light industry, medicine: used to make cheeses, sausages, canned food, are part of detergent powders. They are also used in the manufacture of photographic materials.