What is the enzymatic function of proteins? Enzymatic function of proteins: examples

The work of our body is an extremely complex process, involving millions of cells, thousands of very diverse substances. But there is one area that entirely depends on the special proteins, without which the life of man or animal will be absolutely impossible. As you probably guessed, we are now talking about enzymes.

Today we will consider the enzymatic function of proteins. This is an important area of biochemistry.

Since the basis of these substances are mainly proteins, they themselves can be considered them. It is necessary to know that for the first time enzymes were discovered as far back as the 30s of the 19th century, but it took scientists more than a century to come to a more or less uniform definition for them. So what function does the enzyme protein do? About this, as well as their structure and examples of reactions you will learn from our article.

It should be understood that not every protein can be an enzyme, even theoretically. Only globular proteins are capable of exhibiting catalytic activity against other organic compounds. Like all natural compounds of this class, the enzymes consist of amino acid residues. Remember that the enzymatic function of proteins (examples of which will be in the article) can be performed only by those of them whose molar mass is not less than 5000.

What is an enzyme, modern definitions

Enzymes are catalysts of biological origin. They have the ability to accelerate reactions due to the closest contact between the two reactants (substrates) involved in the reaction. It can be said that the enzymatic function of proteins is the process of catalysis of certain biochemical reactions that are characteristic only of a living organism. Only a small part of them can be reproduced in the laboratory.

It should be noted that in recent years there has been some breakthrough in this direction. Scientists are gradually approaching the creation of artificial enzymes that can be used not only for the national economy, but also for medicine. Enzymes are being developed that can effectively destroy even small areas of the onset of cancer.

Which parts of the enzyme are directly involved in the reaction?

Note that the contact with the substrate does not include the whole body of the enzyme, but only its small area, which is called the active center. This is their main property, complementarity. This concept implies that the enzyme is ideally suited to the substrate in form and its physico-chemical properties. It can be said that the function of protein-enzymes in this case is as follows:

• Their water shell comes off the surface.
• There is a definite deformation (polarization, for example).
• After that, they are located in a special way in space, simultaneously approaching each other.

It is these factors that lead to an acceleration of the reaction. And now let's make a comparison between enzymes and inorganic catalysts.

As you can see, the enzymatic function of proteins assumes specificity. We also add that many of these proteins also have specific specificity. Simply put, human enzymes are unlikely to be suitable for guinea pigs.

Important information about the structure of enzymes

In the structure of these compounds, three levels are immediately distinguished. The primary structure can be identified by the amino acid residues that are part of the enzymes. Since the enzymatic function of proteins, examples of which we repeatedly cite in this article, can be carried out only by certain categories of compounds, it is quite realistic to determine them precisely by this feature.

As for the secondary level, membership is determined by additional types of bonds that can arise between these amino acid residues. These bonds are hydrogen, electrostatic, hydrophobic, and van der Waals interactions. As a result of the stress that these bonds cause, α-helices, loops and β-strands are formed in different parts of the enzyme.

The tertiary structure appears as a result of the relatively large sections of the polypeptide chain simply folding. The resulting strands are called domains. Finally, the final formation of this structure occurs only after a stable interaction is established between different domains. It should be remembered that the formation of the domains themselves takes place in an absolutely independent order.

Some characteristics of domains

Typically, the polypeptide chain from which they are formed consists of approximately 150 amino acid residues. When domains interact with each other, a globule is formed. Since the enzymatic function is performed by the active centers on their basis, the importance of this process should be understood.

The domain itself is distinguished by the fact that numerous interactions are observed between its amino acid residues. Their number is much larger than those for the reactions between the domains themselves. Thus, the cavities between them are relatively "vulnerable" to the action of various organic solvents. Their volume is of the order of 20-30 cubic angstroms, which can accommodate several molecules of water. Different domains often have a completely unique spatial structure, which is associated with the performance of completely different functions.

Active centers

As a rule, active centers are located strictly between domains. Accordingly, each of them plays a very important role in the course of the reaction. Due to this arrangement of domains, considerable flexibility and mobility of this region of the enzyme are found. This is extremely important, since the enzymatic function is performed only by those compounds that can appropriately change their spatial position.

Between the length of the polypeptide bond in the body of the enzyme and the way in which complex functions are performed, there is a direct relationship. Complication of the role is achieved both by forming an active reaction center between the two catalytic domains, and by the formation of completely new domains.

Some enzyme proteins (examples - lysozyme and glycogen phosphorylase) can vary very much in their sizes (129 and 842 amino acid residues, respectively), although they catalyze the cleavage reaction of the same types of chemical bonds. The difference is that more massive and larger enzymes are able to better control their position in space, which ensures greater stability and speed of reaction.

Basic classification of enzymes

At present, the standard classification is common and widespread throughout the world. According to her, six main classes are distinguished, with the corresponding subclasses. We will consider only the basic ones. Here they are:

1. Oxidoreductases. The function of protein-enzymes in this case is stimulation of oxidation-reduction reactions.

2. Transferase. Can carry out the transfer between the substrates of the following groups:

• One-carbon residues.
• Remains of aldehydes, as well as ketones.
• Acyl and glycosyl components.
• Alkyl (as an exception can not carry CH3) residues.
• Nitrogen bases.
• Groups containing phosphorus.

3. Hydrolases. In this case, the value of the enzymatic function of proteins consists in splitting the following types of compounds:

• Esters.
• Glycosides.
• Ethers, as well as thioethers.
• Peptide type bonds.
• Links of type CN (except for all the same peptides).

4. Lyses. They have the ability to disengage groups with the subsequent formation of a double bond. In addition, the reverse process can also be performed: joining separate groups to double bonds.

5. Isomerases. In this case, the enzymatic function of proteins is the catalysis of complex isomeric reactions. This group includes the following enzymes:

• Racemases, epimerases.
• Cisstransisomerase.
• Intramolecular oxidoreductases.
• Intramolecular transferases.
• Intramolecular lyases.

6. Ligases (otherwise known as synthetases). Served for the cleavage of ATP with the simultaneous formation of certain bonds.

It is easy to see that the enzymatic function of proteins is incredibly important, since they to some extent control almost all the reactions that occur in your body every second.

What remains of the enzyme after interaction with the substrate?

Often, the enzyme is a protein of globular origin, the active center of which is represented by its amino acid residues. In all other cases, the center includes a firmly connected prosthetic group or coenzyme (ATP, for example), whose connection is much weaker. The whole catalyst is called a holoenzyme, and its residue, formed after removal of ATP, is an apoenzyme.

Thus, according to this feature, the enzymes are divided into the following groups:

• Simple hydrolases, lyases and isomerases, which do not contain any coenzyme base.
• Protein-enzymes (examples - some transaminases) containing a prosthetic group (lipoic acid, for example). This group also includes many peroxidases.
• Ennisms, for which coenzyme regeneration is mandatory. These include kinases, as well as most of the oxidoreductases.
• Other catalysts, whose composition is not yet fully understood.

All substances that are part of the first group are widely used in the food industry. All other catalysts require very specific conditions for their activation, and therefore work only in the body or in some laboratory experiments. Thus, the enzymatic function is a very specific reaction, which consists in stimulating (catalyzing) certain types of reactions in strictly defined conditions of the human or animal body.

What happens in an active center, or Why do enzymes work so effectively?

We have already said more than once that the key to understanding enzymatic catalysis is the creation of an active center. It is there that a specific binding of the substrate occurs, which under such conditions becomes much more active in the reaction. In order for you to understand the complexity of the reactions conducted there, let's give a simple example: to ferment the glucose, 12 enzymes must be taken at once! Such an uneasy interaction becomes possible solely because the protein performing the enzymatic function has the highest degree of specificity.

Species specificity of enzymes

It can be absolute. In this case, specificity is manifested only to one, strictly defined type of enzyme. Thus, urease interacts only with urea. With lactose milk in the reaction, it will not enter under any circumstances. This is the function of protein-enzymes in the body.

In addition, there is often absolute group specificity. As can be understood from the title, in this case there is "susceptibility" strictly to one class of organic substances (esters, including complex ones, alcohols or aldehydes). Thus, pepsin, which is one of the main enzymes of the stomach, shows specificity only with respect to hydrolysis of the peptide bond. Alcohol dehydrogenase interacts exclusively with alcohols, and lactide dehydrogenase does not break anything except α-hydroxy acids.

It also happens that the enzymatic function is characteristic of a certain group of compounds, but under certain conditions, the enzymes can act on substances quite different from their basic "goal." In this case, the catalyst "gravitates" to a certain class of substances, but under certain conditions it can split other compounds (not necessarily analogous). True, in this case the reaction will go many times slower.

The ability of trypsin to act on peptide bonds is widely known, but very few people know that this protein, performing an enzymatic function in the gastrointestinal tract, can quite easily interact with various ester compounds.

Finally, specificity is optical. These enzymes can interact with the widest range of completely diverse substances, but only on the condition that they have strictly defined optical properties. Thus, the enzymatic function of proteins in this case is largely similar to the principle of action of non-enzymes, and catalysts of inorganic origin.

What factors determine the effectiveness of catalysis?

Today, it is believed that the factors that determine the extremely high degree of enzyme effectiveness are:

• The effect of concentration.
• The effect of spatial orientation.
• Multifunctionality of the active reaction center.

In general, the essence of the concentration effect is no different from that of the inorganic catalysis reaction. In this case, a concentration of the substrate is created in the active center, which is several times greater than the same value for the whole other volume of the solution. At the center of the reaction, the molecules of the substance are selectively sorted, which must react with each other. It is not difficult to guess that this effect leads to an increase in the rate of the chemical reaction by several orders of magnitude.

When a standard chemical process proceeds, it is extremely important which part of the interacting molecules will collide with each other. Simply put, the molecules of matter at the time of the collision must necessarily be strictly oriented with respect to each other. Due to the fact that in the active center of the enzyme such a rotation is performed in a forced manner, after which all the participating components line up in a certain line, the catalysis reaction is accelerated by approximately three orders of magnitude.

Multifunctionality in this case means the property of all components of the active center simultaneously (or strictly coordinated) to act on the molecule of the "processed" substance. Moreover, it (the molecule) is not only properly fixed in space (see above), but also significantly changes its characteristics. All this in combination leads to the fact that enzymes become much easier to act on the substrate in the necessary way.