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Enzyme classification

All enzymes are divided into six main classes:
Oxidoreductases catalyze redox reactions.
Transferases catalyze the intermolecular transfer of chemical groups and residues.
Hydrolases - catalyze the reactions of hydrolytic cleavage of intramolecular bonds.
LiAZ - catalyze the addition reactions of groups by double bonds and the reverse reactions of detachment of such groups.

Isomerases - catalyze isomerization reactions.

Ligases (synthetases) - catalyze the reaction of a compound of two molecules, coupled with the cleavage of the pyrophosphate bond in the adenosine triphosphate molecule (ATP) or similar nucleotide triphosphate.

Each class of enzymes is divided into subclasses, which, in turn, depending on the nature of the enzymatic reaction, are further divided into subclasses, within which are numbered. The most important representatives of certain classes of enzymes are listed in the table (Art. 274). Previously, many enzymes involved in deep cleavage of organic compounds (desmolase) were combined under the general name desmolase (for example, a complex of fermentation enzymes, catalase, carbonic anhydrase, etc.).


Along with a single nomenclature, there are standard units for the expression of enzyme activity: one unit (E) of any enzyme is the amount of enzyme that, under given conditions, catalyzes the conversion of 1 μmol of substrate to 1 minute; enzyme solution concentrations are given in units of activity per 1 ml of solution; molecular activity of the enzyme - expresses the number of substrate molecules (or equivalents of the affected group), converted in 1 minute by one molecule of the enzyme.

Enzymatic reactions, like ordinary chemical reactions, are accelerated with increasing temperature. The temperature optimum of action of enzymes lies within 40-60 °. At a higher temperature, as a rule, inactivation of enzymes occurs. Some enzymes are quite resistant to high temperatures, for example, ribonuclease can withstand temperatures of up to 100 °. Enzymes show maximum activity only at a certain pH value of the medium. Enzyme activity is suppressed by substances called inhibitors (see). The action of inhibitors may be reversible when the activity of enzymes is restored when the inhibitor is removed, and irreversible when the activity of enzymes is practically not restored when the inhibitor is removed.

Enzymes are localized in certain cellular structures. The structural organization of enzyme systems provides a specific sequence of enzymatic reactions and a certain rate of the whole process. For the normal functioning of the enzyme system it is necessary that the activity of all the enzymes contained in it is optimal. If one of the enzymes for one reason or another reduces its activity or falls out of the system, then the activity of the entire enzyme system as a whole is disrupted, which can cause illness of the whole organism. Hence the importance for the diagnosis of the disease to determine the activity and amount of enzymes. In clinical practice, the study of enzymes is of great importance. The most widely studied enzymes are serum (plasma) and whole blood.

Changes in the “enzyme spectrum” of blood can be due to an increase (hyperfermentemia), a decrease (hypofermentemia), or the appearance in the blood of enzymes that are absent in the blood of a healthy person (dysfermentemia). The appearance of non-specific enzymes in the blood may be due to a violation of the permeability of biological membranes, cell destruction or the result of a protective reaction of the body.