The word "enzyme" has Latin roots. In translation, it means "sourdough". In English, the concept "enzyme" is used, derived from the Greek term, meaning the same thing. 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 consider further what constitutes the specificity of the action of enzymes. The types of specificity will also be described in the article.
General characteristics
The manifestation of the catalytic activity of some 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).
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 activethe center is isolated catalytic and substrate sites. The latter is what determines the specificity of enzymes. The substrate is the substance on which the protein acts. Previously, it was believed that their interaction is carried out on the principle of "the key to the castle." In other words, the active site must clearly correspond to the substrate. At present, a different hypothesis prevails. It is believed that there is no exact correspondence initially, but it appears in the course of 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.
Building
All enzymes are divided into one- and two-component. The former have a structure similar to the structure of simple proteins. They contain only amino acids. The second group - proteins - includes protein and non-protein parts. The last is the coenzyme, the first is the apoenzyme. The latter determines the substrate specificity of the enzyme. That is, it performs the function of a substrate site in the active center. The coenzyme, accordingly, acts as a catalytic region. It is related to the specificity of the action. Vitamins, metals, and other low molecular weight compounds can act as coenzymes.
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 take a transitioncondition. In other words, they must have enough strength to pass through the energy barrier. It represents the minimum amount of energy to make all molecules reactive. All catalysts, including enzymes, are capable of lowering the energy barrier. This contributes to the accelerated course of the reaction.
What is the specificity of enzymes?
This ability is expressed in the acceleration of only a certain reaction. Enzymes can act on the same substrate. However, each of them will accelerate only a specific reaction. The reactive specificity of the enzyme can be traced by the example of the pyruvate dehydrogenase complex. It includes proteins that affect PVK. The main ones are: pyruvate dehydrogenase, pyruvate decarboxylase, acetyltransferase. The reaction itself is called oxidative decarboxylation of PVC. Its product is active acetic acid.
Classification
There are the following types of enzyme specificity:
- 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, sucrase reacts exclusively with sucrose, arginase with arginine, and so on.
- Relative. The specificity of the enzymes in thiscase is expressed in the ability of a substance to influence a group of substrates that have a bond of the same type. For example, alpha-amylase reacts with glycogen and starch. They have a glycosidic type bond. Trypsin, pepsin, chymotrypsin affect many proteins of the peptide group.
Temperature
Enzymes have specificity under certain conditions. For most of them, a temperature of + 35 … + 45 degrees is taken as the optimum. When a substance is placed in conditions with lower rates, its activity will decrease. This state is called reversible inactivation. When the temperature rises, his abilities will be restored. It is worth saying that when placed in conditions where t is higher than the indicated values, inactivation will also occur. However, in this case, it will be irreversible, since it will not be restored when the temperature drops. This is due to the denaturation of the molecule.
Influence of pH
The charge of the molecule depends on the acidity. Accordingly, pH affects the activity of the active site and the specificity of the enzyme. The optimal acidity index for each substance is different. However, in most cases it is 4-7. For example, for saliva alpha-amylase, the optimal acidity is 6.8. Meanwhile, there are a number of exceptions. The optimal acidity of pepsin, for example, is 1.5-2.0, chymotrypsin and trypsin are 8-9.
Concentration
The more enzyme present, the faster the reaction rate. Similara conclusion can also be made regarding the concentration of the substrate. However, the saturating content of the target is theoretically determined for each substance. With it, all active centers will be occupied by the available substrate. In this case, the specificity of the enzyme will be maximum, regardless of the subsequent addition of targets.
Regulatory Substances
They can be divided into inhibitors and activators. Both of these categories are divided into non-specific and specific. The activators of the latter type include bile s alts (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 upon cleavage of 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 a terminal hexapeptide, which is a specific inhibitor. In the process of activation, it is split off. The active site of trypsin becomes open as a result. Nonspecific inhibitors are s alts from heavy metals. For example, copper sulfate. They provoke the denaturation of compounds.
Inhibition
It can be competitive. This phenomenon is expressed in the appearance of a structural similarity between the inhibitor and the substrate. They areenter into a struggle for communication with the active center. If the inhibitor content is higher than that of the substrate, a complex enzyme inhibitor is formed. When a target substance is added, the ratio will change. As a result, the inhibitor will be forced out. For example, succinate acts as a substrate for succinate dehydrogenase. Inhibitors are oxaloacetate or malonate. Competitive influences are considered to be reaction products. Often they are similar to 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 similarity between substances. Both the inhibitor and the substrate can bind to the enzyme at the same time. In this case, a new compound is 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 AC. An example is cytochrome oxidase. For this enzyme, oxygen acts as a substrate. Hydrocyanic acid s alts are inhibitors of cytochrome oxidase.
Allosteric regulation
In some cases, in addition to the active center that determines the specificity of the enzyme, there is one more link. It is an allosteric component. If the activator of the same name binds to it, the efficiency of the enzyme increases. If an inhibitor reacts with the allosteric center, then the activity of the substance decreases accordingly. For example, adenylate cyclase andguanylate cyclase are enzymes with regulation of the allosteric type.
