The kinetics of enzymatic reactions is considered in the works of Menten and Michaelis. Scientists have described this issue in detail in the equation of the enzyme-substrate complex.
Definition
The kinetics of enzymatic reactions are considered in the science of enzymes, which studies the dependence of the rate of such a process on the chemical characteristics of the substrate, environment, and foreign factors affecting the course of the chemical reaction.
With a significant concentration of the substrate, it will not affect the speed of the process.
Leakage specificity
The analysis of enzyme activity is carried out at significant concentrations of substrates (zero order chemical process). Under such conditions, only the amount of the enzyme will affect the change in the speed of the process.
The kinetics of enzymatic reactions in living cells has some distinctive characteristics. Enzymes in them are not used to their full potential. With an excessive amount of substrate, which is possible under experimental conditions, the reaction rate will be proportional to the amount of enzyme. With a significant increase in this indicator, a violation of such proportionality is observed.
The action of modulators on enzymes
The kinetics of enzymatic reactions explains the linear increase in the rate of the process with an increase in substrate content. With an excessive increase in its concentration, a decrease in the substrate is observed, and the speed of the chemical process decreases.
The kinetics of enzymatic reactions confirms the dependence of the activity of enzymes on the pH of the medium, the specificity of the enzyme, its amount. Substances that affect the course of such a reaction are called modulators or effectors. They are usually divided into inhibitors and activators that help slow down or accelerate a certain process.
The basics of the kinetics of enzymatic reactions make it possible to fully understand the essence of the effects of these substances. Some of them are considered natural regulators of the metabolic process. There are different types of modulators of enzyme activity, which differ from each other in the mechanism of action and structure.
Activator Options
What characterizes the kinetics of enzymatic reactions? Biochemistry considers bile acids, metal ions, anions as activators. There are situations when one substance in relation to one enzyme will act as an activator, and otherwise it will be an inhibitor. Specific activators for the detection of enzymes are metal ions.
They can stimulate the process of attachment of the substrate to the enzyme, participate in the formation of its tertiary structure, or can act as part of the active center.
What is the kinetics of enzymatic reactions? It can be briefly noted that the cations of many metals are essential components necessary for the full functioning of many enzymes. Some of them require several different ions at once. For example, for ATPase, which produces ion transport through a plasma membrane, magnesium, sodium, and potassium ions are required.
Metals can be part of a prosthetic enzyme group. For example, iron is considered an important component of catalase in the composition of porphyrin compounds. Cobalt is present in the prosthetic group of methyl malonyl isomerase and homocysteine transmethylase, and manganese is necessary for the activation of isocitrate dehydrogenase. There is a group of enzymes that is activated by cAMP. Similar enzymes are called protein kinases. It consists of two subunits:
- catalytic, which contains an active center;
- regulatory, where the cAMP binding center is located.
Only with the interaction of the regulatory center of the enzyme and c-AMP does it acquire activity.
Kinetics of enzymatic reactions: Michaelis constant, flow conditions, all this is considered in detail in physical chemistry.
Enzyme Features
They are compact molecules, have a relative molecular weight of 104, and a diameter of 20A. Enzymes, which are part of globular proteins, are formed when certain peptide bonds connect 20 amino acid residues.
The internal structure of enzymes in biochemistry is characterized by four types of structures:
- primary associated with the genetic code;
- the secondary structure characterizes the spiralization of the chain;
- tertiary determines the spatial folding of the helix of the polypeptide chain;
- Quaternary is associated with the union of globules into an active oligomeric enzyme.
Specificity of single substrate processes
The kinetics of enzymatic reactions of the Michaelis-Menten equation explains the relationship between the rate and substrate concentrations.
In 1903, L. Henry admitted that the enzyme with the substrate forms a kind of intermediate compound. If the enzyme itself is considered E, the substrate S, then the intermediate will be ES.
L. Michaelis took for the analysis of the kinetics of this process a mechanism that includes two stages: reversible, irreversible.
The kinetic equations of these two processes are quite complex. To solve them, stationary concentrations are used. The rate of preparation of the intermediate compound is described by the law of the acting masses, it relates the initial concentrations of the substrate and the enzyme, current indicators, as well as the concentrations of the intermediate and the reaction product.
Solution Features
What are the main kinetics of enzymatic reactions? The table used in physical chemistry allows you to solve a system of equations in the following cases:
- with a decrease in the concentration of starting materials;
- when the amount of product is exceeded in comparison with the intermediate complex.
For enzymatic processes, the velocity ratio is satisfied, at which the second constant significantly exceeds the value of the first. The reason is the instability of the intermediate compound, its insignificant concentration.
By the decision of IUPAC, a constant that allows us to describe the kinetics of the chemical process was called the Michaelis constant.
The linear dependence of the initial velocity on the concentration of the substrate was confirmed experimentally.
The physical meaning of the Michaelis constant
In order to answer this question, take the concentration of the substrate at which the enzyme shows half of its activity. Michaelis constant has the same dimension as the initial concentration of the substrate: mol \ l.
The numerical parameters of this constant value range from 10 -2-10-8 M. In the course of experimental studies, it was found that the Michaelis constant is a function of temperature. It depends on the presence of other substances that play the role of an activator or inhibitor in the process.
Special case
If during the process a state is reached in which equality of constants is observed, equilibrium is established in the system. This makes it possible to apply the approximation of quasi-equilibrium concentrations in the analysis of enzymatic processes.
As a result, the expression for the Michaelis constant is significantly simplified; it characterizes the affinity of the enzyme for the substrate used.
Inhibition of enzymatic processes
Reagents act as such substances, which, when introduced into the reaction system, significantly reduce the rate of interaction. Enzymatic catalysis requires preliminary adsorption of the substrate, its clear orientation with respect to the active groups of the catalytic center, and for inhibition, one can restrict oneself to the usual binding of the inhibitor to some fragments of the adsorption site.
Compound inhibitors can exhibit properties due to the formation of strong complexes (cyanides), as well as when exposed to a carbonyl group with protein denaturation.
Types of inhibition
The effect of a slowdown in chemical interaction is observed for several reasons:
- The inhibitor competes for the active center with the substrate, creating an inactive center with the enzyme. In the case of an increase in substrate concentration, activity in the solution of the enzyme itself is restored.
- The inhibitor attaches to another part of the protein molecule, forming an inactive complex. The enzyme restores its original activity under the influence of other substances, without affecting the substrate.
The speed of the process is related to the rate of formation of the final product through concentration, Michaelis constant. The last value can be determined graphically, as well as expressed mathematically from the formula. With an inactive complex, the inhibitor does not interfere with the reaction between the enzyme and the substrate, but significantly reduces the speed of the process.
During the statistical processing of experimental data, for non-competitive inhibition, it was possible to identify the main parameters, to prove the relationship between the magnitude of the velocity and the concentration indices.
The kinetics of chemical processes involves a description of the features of all stages of chemical processes using constant values, the Michaelis-Menten equation. In the course of experimental studies, a relationship was found between the rate of the enzymatic process and the change in the concentration of the reaction product or the initial substrate.
In addition, a relationship has been established between the rate and nature of the enzyme. It is precisely on its characteristics that the activity and behavior in the course of interaction directly depend. A measure of enzyme activity is considered one standard unit, which characterizes the amount of enzyme that catalyzes the conversion to micromoles of the starting substrate per minute.
Enzymes are widely used in modern medicine, the speed of determining the problem, as well as the quality of the medical diagnosis of the patient, directly depends on their activity.