The word "enzyme" has Latin roots. Translated, it means "leaven." In English, the term "enzyme" is used, derived from the Greek term meaning the same. Enzymes are 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 constitutes the specificity of the action of enzymes. Types of specificity will also be described in the article.
general characteristics
The manifestation of the catalytic activity of some enzymes is determined by 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).
Activity mechanism
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, catalytic and substrate sites are isolated. The latter is what determines the specificity of enzymes. A substrate is a substance on which a protein acts. Previously, it was believed that their interaction is carried out on a key-to-lock basis. In other words, the active center must clearly match the substrate. At present, a different hypothesis prevails. It is believed that exact correspondence is initially absent, however, 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 - proteids - includes protein and non-protein parts. The last is coenzyme, the first is an apoenzyme. The latter determines the substrate specificity of the enzyme. That is, it serves as a substrate site in the active center. Coenzyme, respectively, acts as a catalytic region. The specificity of the action is associated with it. Coenzymes can be vitamins, metals, and other low molecular weight compounds.
Catalysis
The occurrence of any chemical reaction is associated with the collision of molecules of interacting substances. Their movement in the system is determined by the presence of potential free energy. For a chemical reaction, the molecules need to transition. In other words, they must have enough strength to pass the energy barrier. It represents the minimum amount of energy to give all molecules reactivity. All catalysts, including enzymes, are able to lower the energy barrier. This contributes to the accelerated flow of the reaction.
What is the specificity of enzymes?
This ability is expressed in accelerating 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 on the example of the pyruvate dehydrogenase complex. It includes proteins that affect PVC. The main ones are: pyruvate dehydrogenase, pyruvate decarboxylase, acetyltransferase. The reaction itself is called oxidative decarboxylation of PVC. Acetic active acid acts as its product.
Classification
The following types of specificity of enzymes are available:
- Stereochemical. It is expressed in the ability of a substance to influence one of the possible substrate stereoisomers. For example, fumarate hydrotase is able to act on fumarate. However, it does not affect the cis isomer - maleic acid.
- Absolute. The 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.
- Relative. The specificity of enzymes in this case is expressed in the ability of a substance to influence a group of substrates having a bond of the same type. For example, alpha-amylase reacts with glycogen and starch. They have a glycosidic bond type. Trypsin, pepsin, chymotrypsin affect many proteins of the peptide group.
Temperature
Enzymes have specificity under certain conditions. For most of them, the optimum temperature is + 35 ... + 45 degrees. When a substance is placed in conditions with lower rates, its activity will decrease. This condition is called reversible inactivation. With increasing temperature, his abilities will be restored. It is worth saying that when placed in conditions where t will be above the specified values, inactivation will also occur. However, in this case it will be irreversible, since it will not recover when the temperature decreases. This is due to denaturation of the molecule.
PH effect
The charge of a molecule depends on acidity. Accordingly, pH affects the activity of the active center and the specificity of the enzyme. The optimal acidity for each substance is different. However, in most cases, it is 4-7. For example, for saliva alpha-amylase, the optimum acidity is 6.8. Meanwhile, there are a number of exceptions. The optimum acidity of pepsin, for example, 1.5-2.0, chymotrypsin and trypsin - 8-9.
Concentration
The more enzyme present, the higher the reaction rate. A similar conclusion can be made regarding the concentration of the substrate. However, theoretically, for each substance, the saturating content of the target is determined. With it, all active centers will be occupied by the existing substrate. Moreover, the specificity of the enzyme will be maximum, regardless of the subsequent addition of targets.
Regulators
They can be divided into inhibitors and activators. Both of these categories are divided into non-specific and specific. The authors of the latter type include bile salts (for lipase in the pancreas), perchloric ions (for alpha-amylase), hydrochloric acid (for pepsin). Nonspecific activators are magnesium ions that affect kinases and phosphatases, and specific proenzymes are terminal inhibitors. The latter are inactive forms of substances. They are activated by cleaving terminal peptides. Their specific types correspond to each individual proenzyme. For example, inactive form trypsin is produced as trypsinogen. Its active center is closed by the terminal hexapeptide, which is a specific inhibitor. In the process of activation, it is cleaved. The active center of trypsin as a result of this becomes open. Non-specific inhibitors are salts from heavy metals. For example, copper sulfate. They provoke the denaturation of compounds.
Inhibition
It can be competitive. This phenomenon is expressed in the occurrence of structural similarities between the inhibitor and the substrate. They enter the struggle for communication with the active center. If the content of the inhibitor is higher than the substrate, a co-enzyme inhibitor is formed. When a target substance is added, the ratio will change. As a result, the inhibitor will be displaced. For example, succinate for succinate dehydrogenase acts as a substrate. Inhibitors are oxaloacetate or malonate. Competitive are considered influences as reaction products. Often they look like substrates. For example, for glucose-6-phosphate, the product is glucose. The substrate will be glucose-6 phosphate. Non-competitive inhibition does not imply structural similarities between substances. The inhibitor and substrate can simultaneously bind to the enzyme. At the same time, a new compound is being formed. It 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. Cytochrome oxidase inhibitors are hydrocyanic acid salts.
Allosteric regulation
In some cases, in addition to the active center, which determines the specificity of the enzyme, there is another link. It acts as an allosteric component. If an activator of the same name binds to it, the effectiveness of the enzyme increases. If an inhibitor enters into a reaction with an allosteric center, then the activity of the substance, accordingly, decreases. For example, adenylate cyclase and guanylate cyclase are allosteric-regulated enzymes.