The foundations of the kinetics of enzymatic processes were laid down in the works of Michaelis and Menten, in particular, in the equation of the enzyme-substrate complex.

The kinetics of enzymatic processes is understood as a section of the science of enzymes that studies the dependence of the rate of an enzymatic reaction on the chemical nature of the substrate, environmental conditions, and extraneous factors that affect the course of the reaction.
When the substrate concentration is high enough, it no longer affects the rate, because the latter has become maximum (indicating that the entire enzyme is bound to the substrate).
The study of enzyme activity is carried out at high concentrations of substrates (zero order of the reaction). Under these conditions, all changes in the reaction rate will depend only on the amount of enzyme. However, in living cells, substrate concentrations are, as a rule, far from saturation of enzymes. This means that enzymes in cells do not use their full power.
Dependence of the enzymatic reaction rate on the amount of enzyme
If the substrate is in excess, which is practically the case under experimental conditions, then the reaction rate is proportional to the amount of enzyme. But, if the amount of enzyme is increased so that the substrate is not in excess, then this proportionality will be violated.
The rate of the enzymatic reaction increases linearly with the increase in the content of the enzyme. But an excessive increase in the concentration of the enzyme leads to the fact that the substrate becomes less than the enzyme, and this is manifested by a decrease in the increase in the reaction rate.
Effects on enzyme modulators
The activity of enzymes can change not only due to changes in the amount of substrate, enzyme, pH of the medium, but also under the influence of various chemicals. Substances that affect the course of enzymatic reactions are called their modulators, or effectors. They are divided into activators and inhibitors, that is, under their influence, the reaction can be accelerated or slowed down. The study of the action of enzyme modulators is of practical importance, since it allows a deeper understanding of the nature of the action of enzymes. Some of them play the role of natural regulators of metabolism. There are many types of enzyme activity modulators that differ in structure and mechanism of action.
enzyme activators
The role of activators can be played by both organic (bile acids, enzymes, etc.) and inorganic substances (metal ions, anions). Often there are cases when the same substance in relation to one enzyme is an activator, and in relation to another - an inhibitor. Metal ions are very specific activators for certain enzymes. They can contribute to the attachment of the substrate to the enzyme, participate in the formation of the tertiary structure of the enzyme, or be part of the active site. Ions of many metals (sodium, potassium, calcium, magnesium, iron, copper, etc.) are essential components that are necessary for the normal functioning of many enzymes. Sometimes, some enzymes need several different ions. For example, for Na +, K + -ATPase, which transports ions through the plasma membrane, potassium, sodium and magnesium ions are necessary for normal functioning.
Metals can be part of the prosthetic group of enzymes. For example, iron in the composition of porphyrin compounds is a necessary component of the enzymes of the cytochrome system, catalase and peroxidase; cobalt is included in the prosthetic group of homocysteine ​​transmethylase and methylmalonyl isomerase enzymes; copper - to ascorbate oxidase; manganese is an activator of isocitrate dehydrogenase.
Metalloenzymes containing predominantly di- and trivalent ions in their composition form claw-like chelate compounds with the residues of functional groups of amino acids and the corresponding ions. In such compounds, ions provide enzymes with a certain spatial structure and contribute to the formation of enzyme-substrate complexes. Some enzymes in the absence of metals simply do not show enzymatic action. For example, carbonic anhydrase without zinc does not have the properties of an enzyme and the action of zinc cannot be replaced by any other ion.
There is a group of enzymes that are activated by cAMP. Such enzymes are called protein kinases. The mechanism of their activation is as follows. Protein kinase consists of two subunits: a catalytic one containing an active site, and a regulatory one, in which the cAMP binding site is located. The enzyme is inactive because its active site is closed. It is released only by the interaction of c-AMP and the regulatory center of the enzyme.

Enzymatic kinetics studies the influence of various factors (S and E concentration, pH, temperature, pressure, inhibitors and activators) on the rate of enzymatic reactions. The main goal of studying the kinetics of enzymatic reactions is to obtain information that allows a deeper understanding of the mechanism of action of enzymes.

Kinetic curve allows you to determine the initial reaction rate V 0 .

Substrate saturation curve.

Dependence of reaction rate on enzyme concentration.

The dependence of the reaction rate on temperature.

The dependence of the reaction rate on pH.

The optimum pH for the action of most enzymes lies within the physiological range of 6.0-8.0. Pepsin is active at pH 1.5-2.0, which corresponds to the acidity of gastric juice. Arginase, a specific liver enzyme, is active at 10.0. The influence of the pH of the medium on the rate of the enzymatic reaction is associated with the state and degree of ionization of ionogenic groups in the molecule of the enzyme and substrate. This factor determines the conformation of the protein, the state of the active center and substrate, the formation of the enzyme-substrate complex, and the process of catalysis itself.

Mathematical description of the substrate saturation curve, Michaelis constant .

The equation describing the substrate saturation curve was proposed by Michaelis and Menton and bears their names (the Michaelis-Menten equation): V = (V MAX *[ S])/(km+[ S]) , where Km is the Michaelis constant. It is easy to calculate that for V = V MAX /2 Km = [S], i.e. Km is the substrate concentration at which the reaction rate is ½ V MAX . In order to simplify the determination of V MAX and Km, the Michaelis-Menten equation can be recalculated. 1/V = (Km+[S])/(V MAX *[S]), 1/V = Km/(V MAX *[S]) + 1/V MAX ,

1/ V = km/ V MAX *1/[ S] + 1/ V MAX the Lineweaver-Burk equation. The equation describing the Lineweaver-Burk plot is the equation of a straight line (y = mx + c), where 1/V MAX is the segment intercepted by the straight line on the y-axis; Km/V MAX - tangent of the slope of the straight line; the intersection of the straight line with the x-axis gives the value 1/Km. The Lineweaver-Burk plot allows Km to be determined from a relatively small number of points. This graph is also used when evaluating the effect of inhibitors, as will be discussed below. The Km values ​​vary over a wide range: from 10 -6 mol/l for very active enzymes to 10 -2 for inactive enzymes.

Km estimates are of practical value. At substrate concentrations 100 times Km, the enzyme will operate at nearly maximum rate, so the maximum V MAX rate will reflect the amount of active enzyme present. This circumstance is used to assess the content of the enzyme in the preparation. In addition, Km is a characteristic of the enzyme, which is used to diagnose enzymopathies.

Inhibition of enzyme activity.

An extremely characteristic and important feature of enzymes is their inactivation under the influence of certain inhibitors.

Inhibitors - These are substances that cause partial or complete inhibition of reactions catalyzed by enzymes.

Inhibition of enzymatic activity may be irreversible or reversible, competitive or non-competitive.

irreversible inhibition - this is a persistent inactivation of the enzyme resulting from the covalent binding of an inhibitor molecule in the active site or in another special site that changes the conformation of the enzyme. The dissociation of such stable complexes with the regeneration of the free enzyme is practically excluded. To overcome the consequences of such inhibition, the body must synthesize new enzyme molecules.

Reversible inhibition – is characterized by equilibrium complexation of the inhibitor with the enzyme due to non-covalent bonds, as a result of which such complexes are capable of dissociation with the restoration of enzyme activity.

The classification of inhibitors into competitive and non-competitive is based on being attenuated ( competitive inhibition ) or is not weakened ( noncompetitive inhibition ) their inhibitory action with an increase in the concentration of the substrate.

Competitive inhibitors are, as a rule, compounds whose structure is similar to that of the substrate. This allows them to bind in the same active site as the substrates, preventing the interaction of the enzyme with the substrate already at the binding stage. Once bound, the inhibitor can be converted to a product or remain in the active site until dissociation occurs.

Reversible competitive inhibition can be represented as a diagram:

E↔ E-I → E + P 1

S (inactive)

The degree of enzyme inhibition is determined by the ratio of substrate and enzyme concentrations.

A classic example of this type of inhibition is the inhibition of succinate dehydrogenase (SDH) activity by malate, which displaces succinate from the substrate site and prevents its conversion to fumarate:

Covalent binding of the inhibitor to the active site leads to enzyme inactivation (irreversible inhibition). An example irreversible competitive inhibition inactivation of triosephosphate isomerase by 3-chloroacetolphosphate can serve. This inhibitor is a structural analogue of the substrate, dihydroxyacetone phosphate, and irreversibly attaches to the glutamic acid residue in the active site:

Some inhibitors act less selectively, interacting with a certain functional group in the active center of various enzymes. Thus, the binding of iodoacetate or its amide to the SH group of the amino acid cysteine, which is located in the active center of the enzyme and takes part in catalysis, leads to a complete loss of enzyme activity:

R-SH + JCH 2 COOH → HJ + R-S-CH 2 COOH

Therefore, these inhibitors inactivate all enzymes that have SH groups involved in catalysis.

Irreversible inhibition of hydrolases under the action of nerve gases (sarin, soman) is due to their covalent binding to the serine residue in the active center.

The method of competitive inhibition has found wide application in medical practice. Sulfanilamide drugs - antagonists of p-aminobenzoic acid, can serve as an example of metabolizable competitive inhibitors. They bind to dihydropterate synthetase, a bacterial enzyme that converts p-aminobenzoate to folic acid, which is necessary for bacterial growth. The bacterium dies as a result of the fact that the bound sulfanilamide is converted into another compound and folic acid is not formed.

Noncompetitive inhibitors usually bind to the enzyme molecule at a site different from the substrate binding site, and the substrate does not directly compete with the inhibitor. Since the inhibitor and substrate bind to different centers, both the E-I complex and the S-E-I complex can be formed. The S-E-I complex also breaks down to form a product, but at a slower rate than E-S, so the reaction will slow down but not stop. Thus, the following parallel reactions can take place:

E↔ E-I ↔ S-E-I → E-I + P

Reversible non-competitive inhibition is relatively rare.

Non-competitive inhibitors are called allosteric as opposed to competitive isosteric ).

Reversible inhibition can be quantitatively studied based on the Michaelis-Menten equation.

With competitive inhibition, V MAX remains constant, while Km increases.

With non-competitive inhibition, V MAX decreases with unchanged Km.

If the reaction product inhibits the enzyme that catalyzes its formation, this method of inhibition is called retroinhibition or feedback inhibition . For example, glucose inhibits glucose-6-phosphatase, which catalyzes the hydrolysis of glucose-6-phosphate.

The biological significance of this inhibition is the regulation of certain metabolic pathways (see next session).

PRACTICAL PART

Assignment to students

1. To study the denaturation of proteins under the action of solutions of mineral and organic acids and when heated.

2. Detect NAD coenzyme in yeast.

3. Determine amylase activity in urine (blood serum).

9. STANDARDS OF ANSWERS TO TASKS, test questions used in the control of knowledge in the classroom (can be in the form of an application)

10. NATURE AND SCOPE OF POSSIBLE TRAINING AND RESEARCH WORK ON THE TOPIC

(Indicate specifically the nature and form of UIRS: preparation of abstract presentations, independent research, simulation game, registration of a medical history using monographic literature, etc. forms)

Enzymatic kinetics studies the influence of the chemical nature of reacting substances (enzymes, substrates) and the conditions of their interaction (pH, temperature, concentration, presence of activators or inhibitors) on the rate of an enzymatic reaction. The enzymatic reaction rate (u) is measured by the decrease in the amount of substrate or the increase in the reaction product per unit of time.

At a low substrate concentration, the reaction rate

directly proportional to its concentration. At a high substrate concentration, when all active sites of the enzyme are occupied by the substrate ( saturation of the enzyme with the substrate), the reaction rate is maximum, becomes constant and does not depend on the concentration of the substrate [S] and completely depends on the concentration of the enzyme (Fig. 19).

K S is the dissociation constant of the enzyme-substrate complex ES, inverse to the equilibrium constant:

.

The lower the K S value, the higher the affinity of the enzyme for the substrate.

Rice. 19. Dependence of the rate of the enzymatic reaction on the concentration of the substrate at a constant concentration of the enzyme

The quantitative relationship between the concentration of the substrate and the rate of the enzymatic reaction expresses Michaelis-Menten equation:

,

u is the reaction rate, u max is the maximum rate of the enzymatic reaction.

Briggs and Haldane improved the equation by introducing into it Michaelis constant K m determined experimentally.

Briggs–Haldane equation:

,

.

The Michaelis constant is numerically equal to the substrate concentration (mol/l) at which the enzymatic reaction rate is half of the maximum (Fig. 20). K m shows the affinity of the enzyme to the substrate: the smaller its value, the greater the affinity.

Experimental values ​​of K m for most enzymatic reactions involving a single substrate are usually 10 -2 -10 -5 M. If the reaction is reversible, then the interaction of the enzyme with the substrate of the direct reaction is characterized by K m that differs from that for the substrate of the reverse reaction.

G. Lineweaver and D. Burke transformed the Briggs-Haldane equation and obtained the equation of a straight line: y = ax + b (Fig. 21):

.

The Lineweaver-Burk method gives a more accurate result.

Rice. 21. Graphical definition of the Michaelis constant

according to the Lineweaver-Burk method

PROPERTIES OF ENZYMES

Enzymes differ from conventional catalysts in a number of ways.

Thermolability, or sensitivity to temperature increase (Fig. 22).

Rice. 22. Dependence of the enzymatic reaction rate on temperature

At a temperature not exceeding 45–50 °C, the rate of most biochemical reactions increases by a factor of 2 with an increase in temperature by 10 °C according to the van't Hoff rule. At temperatures above 50 °C, the rate of reaction is affected by thermal denaturation of the enzyme protein, gradually leading to its complete deactivation.

The temperature at which the catalytic activity of an enzyme is maximum is called its temperature optimum. The temperature optimum for most mammalian enzymes is in the range of 37-40 °C. At low temperatures (0 °C and below), enzymes, as a rule, are not destroyed, although their activity decreases almost to zero.

Dependence of the enzyme activity on the pH value of the medium(Fig. 23).

For each enzyme, there is an optimal pH value of the medium at which it exhibits maximum activity. pH optimum The action of animal tissue enzymes lies within a narrow zone of hydrogen ion concentration, corresponding to the physiological pH values ​​of 6.0-8.0 developed in the process of evolution. Exceptions are pepsin - 1.5-2.5; arginase - 9.5-10.

Rice. 23. Dependence of the enzymatic reaction rate on the pH of the medium

The influence of changes in the pH of the medium on the enzyme molecule consists in the effect on the degree of ionization of its active groups, and, consequently, on the tertiary structure of the protein and the state of the active center. pH also changes the ionization of cofactors, substrates, enzyme-substrate complexes, and reaction products.

Specificity. The high specificity of the action of enzymes is due to the conformational and electrostatic complementarity between the molecules of the substrate and the enzyme and the unique structural organization of the active center, which ensure the selectivity of the reaction.

Absolute specificity - the ability of an enzyme to catalyze a single reaction. For example, urease catalyzes the hydrolysis of urea to NH3 and CO2, while arginase catalyzes the hydrolysis of arginine.

Relative (group) specificity - the ability of an enzyme to catalyze a group of reactions of a certain type. Relative specificity, for example, is possessed by hydrolytic peptidase enzymes, which hydrolyze peptide bonds in molecules of proteins and peptides, and lipase, which hydrolyzes ester bonds in fat molecules.

stereochemical specificity possess enzymes that catalyze the transformation of only one of the spatial isomers. The fumarase enzyme catalyzes the conversion of the trans-isomer of butenedioic acid, fumaric acid, into malic acid, and does not act on the cis-isomer, maleic acid.

The high specificity of the action of enzymes ensures that only certain chemical reactions occur out of all possible transformations.

Enzyme Properties

1. Dependence of the reaction rate on temperature

The dependence of enzyme activity (reaction rate) on temperature is described bell curve with a maximum speed at values optimal temperature for a given enzyme. The increase in the reaction rate as the optimum temperature is approached is explained by the increase in the kinetic energy of the reacting molecules.

Temperature dependence of the reaction rate

The law on the increase in the reaction rate by 2-4 times with an increase in temperature by 10°C is also valid for enzymatic reactions, but only in the range up to 55-60°C, i.e. up to temperatures denaturation proteins. With a decrease in temperature, the activity of enzymes decreases, but does not disappear completely.

As an exception, there are enzymes of some microorganisms that exist in the water of hot springs and geysers; their optimum temperature approaches the boiling point of water. An example of weak activity at low temperatures is the hibernation of some animals (ground squirrels, hedgehogs), whose body temperature drops to 3-5°C. This property of enzymes is also used in surgical practice during operations on the chest cavity, when the patient is subjected to cooling to 22°C.

Enzymes can be very sensitive to temperature changes:

• Siamese cats have a black muzzle, tips of the ears, tail, paws. In these areas, the temperature is only 0.5 ° C lower than in the central regions of the body. But this allows the enzyme that forms the pigment in the hair follicles to work, with the slightest increase in temperature, the enzyme is inactivated,
• the opposite case - when the ambient temperature drops in the hare, the pigment-forming enzyme is inactivated and the hare gets a white coat,
• antiviral protein interferon begins to be synthesized in cells only when the body temperature reaches 38 ° C,

There are also unique situations:

• for most people, an increase in body temperature by 5°C (up to 42°C) is incompatible with life due to an imbalance in the rate of enzymatic reactions. At the same time, it was found in some athletes that during marathon running their body temperature was about 40°C, the maximum recorded body temperature was 44°C.

2. Dependence of the reaction rate on pH

Dependency is also described bell curve with maximum speed at optimal for this enzyme pH value.

This feature of enzymes is essential for the body in its adaptation to changing external and internal conditions. Shifts in the pH value outside and inside the cell plays a role in the pathogenesis of diseases by changing the activity of enzymes of various metabolic pathways.

For each enzyme, there is a certain narrow pH range of the medium, which is optimal for the manifestation of its highest activity. For example, the optimal pH values ​​for pepsin are 1.5-2.5, trypsin 8.0-8.5, salivary amylase 7.2, arginase 9.7, acid phosphatase 4.5-5.0, succinate dehydrogenase 9.0.

The dependence of the reaction rate on the pH value

The dependence of activity on the acidity of the medium is explained by the presence of amino acids in the structure of the enzyme, the charge of which changes with a shift in pH (glutamate, aspartate, lysine, arginine, histidine). A change in the charge of the radicals of these amino acids leads to a change in their ionic interaction during the formation of the tertiary structure of the protein, a change in its charge and the appearance of a different configuration of the active center and, therefore, the substrate binds or does not bind to the active center.

Changes in the activity of enzymes with a shift in pH can also adaptive functions. For example, in the liver, gluconeogenesis enzymes require a lower pH than glycolysis enzymes, which is successfully combined with acidification of body fluids during fasting or exercise.

For most people, shifts in blood pH beyond 6.8-7.8 (at a rate of 7.35-7.45) are incompatible with life due to an imbalance in the rate of enzymatic reactions. At the same time, some marathon runners showed a decrease in blood pH at the end of the distance to 6.8-7.0. And yet they kept working!

3. Dependence on the amount of enzyme

With an increase in the number of enzyme molecules, the reaction rate increases continuously and is directly proportional to the amount of enzyme, because more enzyme molecules produce more product molecules.

Almost all biochemical reactions are enzymatic. Enzymes(biocatalysts) are substances of a protein nature activated by metal cations. About 2000 different enzymes are known, and about 150 of them have been isolated, some of which are used as drugs. Trypsin and chymotrypsin are used to treat bronchitis and pneumonia; pepsin - for the treatment of gastritis; plasmin - for the treatment of heart attack; pancreatin - for the treatment of the pancreas. Enzymes differ from conventional catalysts in (a) higher catalytic activity; (b) high specificity, i.e. selective action.

The mechanism of a single-substrate enzymatic reaction can be represented by the scheme:

where E is an enzyme,

S - substrate,

ES - enzyme-substrate complex,

R is the product of the reaction.

The characteristic of the first stage of the enzymatic reaction is Michaelis constant (K M). K M is the reciprocal of the equilibrium constant:

the Michaelis constant (KM) characterizes the stability of the enzyme-substrate complex (ES). The smaller the Michaelis constant (KM), the more stable the complex.

The rate of an enzymatic reaction is equal to the rate of its rate-limiting step:

where k 2 is the rate constant, called number of revolutions or molecular activity of the enzyme.

molecular activity of an enzyme(k 2) is equal to the number of substrate molecules undergoing transformations under the influence of one enzyme molecule in 1 minute at 25 0 C. This constant takes values ​​in the range: 1 10 4< k 2 < 6·10 6 мин‾ 1 .

For urease, which accelerates the hydrolysis of urea, k 2 = 1.85∙10 6 min‾ 1; for adenosine triphosphatase, which accelerates the hydrolysis of ATP, k 2 = 6.24∙10 6 min‾ 1; for catalase, which accelerates the decomposition of H 2 O 2, k 2 = 5∙10 6 min‾ 1.

However, the kinetic equation of the enzymatic reaction in the form in which it is given above is practically impossible to use due to the impossibility of experimentally determining the concentration of the enzyme-substrate complex (). Expressing in terms of other quantities, easily determined experimentally, we obtain the kinetic equation of enzymatic reactions, called Michaelis-Menten equation (1913):

,

where the product k 2 [E]tot is the value of the constant, which is denoted by (maximum speed).

Respectively:

Consider special cases of the Michaelis-Menten equation.

1) At a low substrate concentration, K M >> [S], therefore

which corresponds to the kinetic equation of the first order reaction.

2) At a high concentration of the substrate K m<< [S], поэтому

which corresponds to the kinetic equation of the zero order reaction.

Thus, at a low substrate concentration, the enzymatic reaction rate increases with an increase in the substrate content in the system, and at a high substrate concentration, the kinetic curve reaches a plateau (the reaction rate does not depend on the substrate concentration) (Fig. 30).

Figure 30. - Kinetic curve of the enzymatic reaction

If [S] = K M, then

which allows you to graphically determine the Michaelis constant K m (Fig. 31).

Figure 31. - Graphical definition of the Michaelis constant

Enzyme activity is influenced by: (a) temperature, (b) acidity of the medium, (c) the presence of inhibitors. The effect of temperature on the rate of an enzymatic reaction is discussed in chapter 9.3.

The influence of the acidity of the medium on the rate of the enzymatic reaction is shown in Figure 32. The maximum activity of the enzyme corresponds to the optimal value of the pH value (pH opt).

Figure 32. - Influence of the acidity of solutions on the activity of enzymes

For most enzymes, the optimal pH values ​​coincide with physiological values ​​(7.3 - 7.4). However, there are enzymes that require a strongly acidic (pepsin - 1.5-2.5) or fairly alkaline environment (arginase - 9.5 - 9.9) for their normal functioning.

Enzyme inhibitors- These are substances that occupy part of the active centers of the enzyme molecules, as a result of which the rate of the enzymatic reaction decreases. Heavy metal cations, organic acids and other compounds act as inhibitors.

Lecture 11

The structure of the atom

There are two definitions of the term "atom". Atom is the smallest particle of a chemical element that retains its chemical properties.

Atom is an electrically neutral microsystem consisting of a positively charged nucleus and a negatively charged electron shell.

The doctrine of the atom has come a long way of development. The main stages in the development of atomistics include:

1) natural-philosophical stage - the period of formation of the concept of the atomic structure of matter, not confirmed by experiment (5th century BC - 16th century AD);

2) the stage of formation of the hypothesis about the atom as the smallest particle of a chemical element (XVIII-XIX centuries);

3) the stage of creating physical models that reflect the complexity of the structure of the atom and make it possible to describe its properties (beginning of the 20th century)

4) the modern stage of atomistics is called quantum mechanical. Quantum mechanics is a branch of physics that studies the motion of elementary particles.

PLAN

11.1. The structure of the nucleus. Isotopes.

11.2. Quantum-mechanical model of the electron shell of the atom.

11.3. Physical and chemical characteristics of atoms.

The structure of the nucleus. isotopes

atom nucleus- This is a positively charged particle, consisting of protons, neutrons and some other elementary particles.

It is generally accepted that the main elementary particles of the nucleus are protons and neutrons. Proton (p) - it is an elementary particle whose relative atomic mass is 1 amu and whose relative charge is + 1. Neutron (n) - it is an elementary particle that does not have an electric charge, the mass of which is equal to the mass of a proton.

The nucleus contains 99.95% of the mass of an atom. Special nuclear forces of extension act between elementary particles, significantly exceeding the forces of electrostatic repulsion.

The fundamental characteristic of an atom is charge his nuclei, equal to the number of protons and coinciding with the serial number of the element in the periodic system of chemical elements. A collection (type) of atoms with the same nuclear charge is called chemical element. Elements with numbers from 1 to 92 are found in nature.

isotopes- These are atoms of the same chemical element containing the same number of protons and a different number of neutrons in the nucleus.

where the mass number (A) is the mass of the nucleus, z is the charge of the nucleus.

Each chemical element is a mixture of isotopes. As a rule, the name of isotopes coincides with the name of a chemical element. However, special names have been introduced for hydrogen isotopes. The chemical element hydrogen is represented by three isotopes:

Number p Number n

Protium H 1 0

Deuterium D 1 1

Tritium T 1 2

Isotopes of a chemical element can be either stable or radioactive. Radioactive isotopes contain nuclei that spontaneously collapse with the release of particles and energy. The stability of a nucleus is determined by its neutron-proton ratio.

Getting into the body, radionuclides disrupt the course of the most important biochemical processes, reduce immunity, doom the body to diseases. The body protects itself from the effects of radiation by selectively absorbing elements from the environment. Stable isotopes take precedence over radioactive isotopes. In other words, stable isotopes block the accumulation of radioactive isotopes in living organisms (Table 8).

S. Shannon's book "Nutrition in the Atomic Age" provides the following data. If a blocking dose of a stable isotope of iodine, equal to ~100 mg, is taken no later than 2 hours after I-131 enters the body, then the absorption of radioiodine in the thyroid gland will decrease by 90%.

Radioisotopes are used in medicine

for the diagnosis of certain diseases,

for the treatment of all forms of cancer,

for pathophysiological studies.

Table 8 - Blocking effect of stable isotopes