Active center of the enzyme: structure, properties. Who discovered the active center of the enzyme? What is called the active center of the enzyme?

We've all heard about enzymes, but it's unlikely that we all know how exactly these substances are arranged and why they are needed. This article will help to understand the structure and functions of enzymes (enzymes) in general and their active centers in particular.

History of research

In 1833 the French chemist Anselm Payen discovered and described the properties of the enzyme amylase.

Several years later, Louis Pasteur, studying the conversion of sugar into alcohol with the participation of yeast, suggested that this process is due to the chemical substances that make up the yeast.

At the end of the XIX century, physiologist Willie Kühne first introduced the term "enzyme".

The German Eduard Buchner in 1897 singled out and described the zymase, an enzymatic complex that catalyzes the reaction of the conversion of sucrose to ethyl alcohol. In nature, zymase is found in large quantities in yeast.

It is not known exactly when and who discovered the active center of the enzyme. This discovery is attributed to the Nobel Prize winner chemist Eduard Buchner, American biologist James Sumner and other well-known scientists who worked on the study of enzymatic catalysis.

General Information on Enzymes

Recall that enzymes are substances of protein nature that perform in living organisms as catalysts for chemical reactions. In the enzyme there are areas that do not directly take part in this, the course of the reaction provides the active center of the enzyme.

We give some properties of enzymes:

1) Efficiency. A small amount of catalyst is sufficient to accelerate the chemical reaction 10 ⁶ times.

2) Specificity. One enzyme is not a universal catalyst for any reaction in the cell. For enzymes, the specificity of the action is expressed: each enzyme catalyzes only one or several reactions with similar substrates (initial reagents), but for reagents of a different chemical nature the same enzyme can be useless. Interaction with suitable substrates and further acceleration of the reaction provides the active center of the enzyme.

3) Variable activity. The activity of enzymes in the cell is constantly changing from low to high.

4) The concentration of certain enzymes in the cell is not constant and can vary depending on external conditions. Such enzymes are called inducible in biology.

Classification of enzymes

By its structure, it is common to divide enzymes into simple and complex ones. Simple consists exclusively of amino acid residues, complex compounds have a non-protein group. Complex are called coenzymes.

By type of catalyzed reactions, enzymes are divided into:

1) Oxidoreductases (catalyze redox reactions).

2) Transferases (carry separate groups of atoms).

3) Liases (cleavage chemical bonds).

4) Lipases (form bonds in the reactions due to the energy of ATP).

5) Isomerases (are involved in the reactions of mutual conversion of isomers).

6) Hydrolases (catalyze chemical reactions with hydrolytic bond cleavage).

Structure of the enzyme

The enzyme is a complex three-dimensional structure, which consists mainly of amino acid residues. Also there is a prosthetic group - a component of a non-protein nature, associated with amino acid residues.

Enzymes are basically globular proteins that can be combined into complex complexes. Like other substances of a protein nature, enzymes are denatured when the temperature rises or under the influence of certain chemical reagents. During the denaturation, the tertiary structure of the enzyme changes and, accordingly, the properties of the active center of the enzymes. As a result, the activity of the enzyme decreases sharply.

The catalyzed substrate is usually much smaller than the enzyme itself. The simplest enzyme consists of sixty amino acid residues, and its active center is only two.

There are enzymes, the catalytic site of which is not represented by amino acids, but a prosthetic group of organic or (more often) inorganic origin - cofactor.

The concept of an active center

Only a small part of the enzyme takes a direct part in chemical reactions. This part of the enzyme is called the active center. The active center of the enzyme is a lipid, several amino acid residues or a prosthetic group that binds to the substrate and catalyzes the reaction. Amino acid residues of the active site can belong to any amino acids - polar, nonpolar, charged, aromatic, uncharged.

The active center of the enzyme (it is a lipid, amino acids or other substances capable of interacting with reagents) is the most important part of the enzyme; without it, these substances would be useless.

Typically, the enzyme molecule has only one active site that binds to one or more similar reagents. Amino acid residues of the active center form hydrogen, hydrophobic or covalent bonds, forming an enzyme-substrate complex.

Structure of the active center

The active center of simple and complex enzymes is a pocket or a slit. This structure of the active center of the enzyme must correspond electrostatically and geometrically to the substrate, since a change in the tertiary structure of the enzyme can change the active site.

The binding and catalytic center are the sites of the active center of the enzyme. Obviously, the binding center "checks" the substrate for compatibility and communicates with it, and the catalytic center takes a direct part in the reaction.

Binding of active center to substrate

In order to explain how the active center of the enzyme binds to a particular reagent, several theories have been proposed. The most popular of these is Fisher's theory, it is also the theory of "lock and key". Fischer suggested that there is an enzyme that is ideally suited to each substrate in terms of its physicochemical properties. After the formation of the enzyme-substrate complex, no modification takes place.

Another American scientist, Daniel Koschland, supplemented Fisher's theory with the assumption that the active center of the enzyme can change its conformation until it reaches a certain substrate.

Kinetics of enzymatic reactions

Features of the course of enzymatic reactions are studied by a separate branch of biochemistry - enzymatic kinetics. This science studies the features of the course of reactions at various concentrations of enzymes and substrates, the dependence of the reaction rate on the temperature inside the cell, and the properties of the active center of enzymes, depending on the change in the physical and chemical parameters of the medium.

Enzymatic kinetics operates with such concepts as reaction rate, activation energy, activation barrier, molecular activity, specific activity, etc. Let us consider some of these concepts.

In order for a biological reaction to occur, the reagents need to transfer some energy. This energy is called the activation energy.

Adding an enzyme to the reagents can reduce the activation energy. Some substances react without the participation of enzymes, since the activation energy is too high. The equilibrium of the reaction does not shift with the addition of the enzyme.

The reaction rate is the amount of the reaction product that appears or disappears per unit time.

The dependence of the reaction rate on the concentration of the substrate is characterized by a dimensionless physical quantity, the Michaelis constant.

Molecular activity - the number of molecules of the substrate, converted by one molecule of the enzyme per unit time.