Specificity of the enzyme: types and features of the action

The word "enzyme" has Latin roots. In translation, it means "leaven". In English, the term "enzyme" is used, derived from the Greek term meaning the same. Enzymes are called specialized proteins. They are formed in cells and have the ability to accelerate the course of biochemical processes. In other words, they act as biological catalysts. Let us further consider what the specificity of the action of enzymes is. также будут описаны в статье. Specificity types will also be described in the article.

general characteristics

The manifestation of the catalytic activity of certain enzymes is due to the presence of a number of non-protein compounds. They are called cofactors. They are divided into 2 groups: metal ions and a number of inorganic substances, as well as coenzymes (organic compounds).

The mechanism of activity

By their chemical nature, enzymes belong to the group of proteins. However, unlike the latter, the elements under consideration contain an active center. It is a unique complex of functional groups of amino acid residues. They are strictly oriented in space due to the tertiary or quaternary structure of the enzyme. In the active center, the catalytic and substrate regions are isolated. The latter is what determines the specificity of enzymes. The substrate is the substance that the protein acts on. Previously it was believed that their interaction is carried out on the principle of "key to the lock." In other words, the active center must clearly correspond to the substrate. Currently, a different hypothesis prevails. It is believed that the exact correspondence is initially absent, but it appears during the interaction of substances. The second - catalytic - site affects the specificity of the action. In other words, it determines the nature of the accelerated reaction.

Structure

All enzymes are divided into one- and two-component. The former have a structure similar to that of simple proteins. They contain exclusively amino acids. The second group - the protein - includes the protein and non-protein parts. The last is coenzyme, the first is apoenzyme. The latter determines the substrate specificity of the enzyme. That is, it acts as a substratum in the active center. Coenzyme, respectively, acts as a catalytic region. The specificity of the action is associated with it. As coenzymes, vitamins, metals, and other low-molecular compounds can act.

Catalysis

The occurrence of any chemical reaction is associated with the collision of molecules of interacting substances. Their motion in the system is determined by the presence of potential free energy. For a chemical reaction, it is necessary that the molecules adopt a transition state. In other words, they must have enough strength to pass through the energy barrier. It represents the minimum volume of energy for giving all molecules reactivity. All catalysts, enzymes including, are able to reduce the energy barrier. This promotes an accelerated flow of the reaction.

What is the specificity of enzymes?

This ability is expressed in the acceleration of only a certain reaction. Enzymes can affect the same substrate. However, each of them will accelerate only a specific reaction. The reactive specificity of the enzyme can be traced to the example of the pyruvate dehydrogenase complex. It includes proteins that affect the PVC. The main ones are: pyruvate dehydrogenase, pyruvate decarboxylase, acetyltransferase. The reaction itself is called oxidative decarboxylation of PVC. As its product acts acetic acid.

Classification

There are following types of enzyme specificity:

1. Stereochemical. It is expressed in the ability of a substance to influence one of the possible substrate stereoisomers. For example, fumarate hydratase is able to act on fumarate. However, it does not affect the cis-isomer-maleic acid.
2. Absolute. этого типа выражается в способности вещества влиять только на конкретный субстрат. Specificity of enzymes of this type is expressed in the ability of a substance to affect only a specific substrate. For example, sucrose reacts exclusively with sucrose, arginase - with arginine and so on.
3. Relative. в этом случае выражена в способности вещества влиять на группу субстратов, имеющих связь одинакового типа. The specificity of enzymes in this case is expressed in the ability of a substance to affect a group of substrates having a bond of the same type. For example, alpha-amylase reacts with glycogen and starch. They have a glycoside-type bond. Trypsin, pepsin, chymotrypsin affect many proteins of the peptide group.

Temperature

в определенных условиях. Enzymes have specificity under certain conditions. For most of them, the optimum temperature is + 35 ... + 45 deg. When the substance is placed in conditions with lower values, its activity will decrease. This condition is called reversible inactivation. As the temperature rises, his abilities will be restored. It is worth mentioning that, if placed in conditions where t is higher than the specified values, inactivation will also occur. However, in this case it will be irreversible, since it does not recover with decreasing temperature. This is due to the denaturation of the molecule.

Effect of pH

The charge of the molecule depends on the acidity. Accordingly, the pH affects the activity of the active site and the specificity of the enzyme. The optimum acidity index for each substance is different. However, in most cases it is 4-7. For example, for alpha salivary amylase, the optimum acidity is 6.8. Meanwhile, there are a number of exceptions. Optimum acidity of pepsin, for example, 1.5-2.0, chymotrypsin and trypsin - 8-9.

Concentration

The more the enzyme is present, the higher the reaction rate. A similar conclusion can be drawn about the concentration of the substrate. However, in theory, the saturating content of the target is determined for each substance. With it all active centers will be occupied by the existing substrate. будет максимальной, вне зависимости от последующего добавления мишеней. In this case, the specificity of the enzyme will be maximal, regardless of the subsequent addition of the targets.

Substances-regulators

They can be divided into inhibitors and activators. Both these categories are divided into nonspecific and specific. The latter type of avtivators include bile salts (for lipase in the pancreas), chloride ions (for alpha-amylase), hydrochloric acid (for pepsin). Nonspecific activators are magnesium ions that affect kinases and phosphatases, and specific inhibitors are terminal peptides of proenzymes. The latter are inactive forms of substances. They are activated by cleavage of the terminal peptides. Their specific types correspond to each individual proenzyme. For example, in an inactive form, trypsin is produced in the form of trypsinogen. Its active center is closed by the terminal hexapeptide, which is a specific inhibitor. In the process of activation, it splits off. The active center of trypsin as a result of this becomes open. Nonspecific inhibitors are salts from heavy metals. For example, copper sulfate. They provoke the denaturation of the compounds.

Inhibition

It can be competitive. This phenomenon is expressed in the occurrence of a structural similarity between the inhibitor and the substrate. They enter into a struggle for communication with the active center. If the content of the inhibitor is higher than that of the substrate, a coplex-enzyme inhibitor is formed. When the target substance is added, the ratio will change. As a result, the inhibitor will be dislodged. For example, succinate for succinate dehydrogenase acts as a substrate. The inhibitors are oxaloacetate or malonate. The influence of reaction products is considered competitive. Often they are like substrates. For example, for glucose-6-phosphate, the product is glucose. The substrate will be glucose-6 phosphate. Noncompetitive inhibition does not imply a structural similarity between substances. The inhibitor and the substrate can simultaneously bind to the enzyme. This leads to the formation of a new compound. He is a complex enzyme-substrate-inhibitor. During the interaction, the active center is blocked. This is due to the binding of the inhibitor to the catalytic site of the AC. An example is cytochrome oxidase. For this enzyme, oxygen acts as a substrate. Inhibitors of cytochrome oxidase are salts of hydrocyanic acid.

Allosteric Regulation

In some cases, in addition to the active center that determines the specificity of the enzyme, there is one more link. The allosteric component acts as it. If an activator of the same name is associated with it, the effectiveness of the enzyme is increased. If the inhibitor enters the reaction with the allosteric center, then the activity of the substance, respectively, decreases. For example, adenylate cyclase and guanylate cyclase refer to enzymes with the regulation of the allosteric type.