Inorganic catalysts and enzymes (biocatalysts), without being consumed themselves, accelerate the course of chemical reactions and their energy capabilities. In the presence of any catalysts, the energy in chemical system keeps constant. In the process of catalysis, the direction chemical reaction remains unchanged.

What are enzymes and inorganic catalysts

Enzymes are biological catalysts. Their basis is protein. The active part of enzymes contains inorganic matter, for example, metal atoms. In this case, the catalytic efficiency of the metals included in the enzyme molecule increases millions of times. It is noteworthy that the organic and inorganic fragments of the enzyme are not able to exhibit the properties of a catalyst separately, while in tandem they are powerful catalysts.
Inorganic catalysts speed up all kinds of chemical reactions.

Comparison of enzymes and inorganic catalysts

What is the difference between enzymes and inorganic catalysts? Inorganic catalysts are inherently not organic matter and enzymes are proteins. As part of inorganic catalysts no protein.
Enzymes, in comparison with inorganic catalysts, have a specificity of action to the substrate and the most high efficiency. Thanks to enzymes, the reaction proceeds millions of times faster.
For example, hydrogen peroxide decomposes rather slowly without the presence of catalysts. In the presence of an inorganic catalyst (usually iron salts), the reaction is somewhat accelerated. And when the enzyme catalase is added, the peroxide decomposes at an unimaginable rate.
Enzymes are able to work in a limited temperature range (usually 370 C). The rate of action of inorganic catalysts with each increase in temperature by 10 degrees increases by 2-4 times. Enzymes are subject to regulation (there are enzyme inhibitors and activators). Inorganic catalysts are characterized by unregulated operation.
Enzymes are characterized by conformational lability (their structure undergoes minor changes that are formed in the process of breaking old bonds and forming new bonds, the strength of which is weaker). Reactions involving enzymes proceed only under physiological conditions. Enzymes are able to work inside the body, its tissues and cells, where the necessary temperature, pressure and pH are created.

TheDifference.ru determined that the difference between enzymes and inorganic catalysts is as follows:

Enzymes - high molecular weight protein bodies, they are quite specific. Enzymes can only catalyze one type of reaction. They are catalysts for biochemical reactions. Inorganic catalysts speed up various reactions.
Enzymes can act in a specific narrow temperature range, a certain pressure and acidity of the medium.
Enzymatic reactions are fast.

Question 18. Similarities and differences between enzymes and inorganic catalysts. Dependence of the rate of enzymatic reactions on temperature, pH. Types of specificity.

The structure of simple and complex enzymes (on the example of hydrolases, dehydrogenases).

By composition, enzymes are divided into simple and complex.

Simple enzymes are made up of amino acids. These include enzymes of the gastrointestinal tract - α-amylase, pepsin, trypsin, lipase, etc. All these enzymes belong to the 3rd class - hydrolases.

Complex enzymes consist of a protein part - an apoenzyme and a non-protein part - a cofactor. The catalytically active enzyme-cofactor complex is called a holoenzyme. As cofactors, both metal ions and organic compounds, many of which are derivatives of vitamins.

For example, oxidoreductases are used as cofactors Fe²+, Сu²+, Mn²+, Mg²+ kinase; glutathione peroxidase, an enzyme that detoxifies hydrogen peroxide, requires selenium.

Coenzymes are organic substances that are loosely bound to the protein part. For example, NAD-dependent dehydrogenases consist of protein and coenzymes NAD, NADP, vitamin PP derivatives.

The prosthetic group is the coenzymes that are firmly (often covalently) bound to the apoenzyme. For example, flavin dehydrogenases consist of protein and prosthetic groups FAD, FMN, vitamin B 2 derivatives. Apoenzyme determines the direction or specificity of the action of the enzyme.

. General properties enzymes: specificity, influence of temperature, pH of the medium on the activity of enzymes.

Enzyme activity is influenced by temperature, pH, ionic strength solutions.

Since the enzymes chemical nature are proteins, an increase in temperature above 45-50 ° C leads to thermal denaturation and enzymes are inactivated (with the exception of muscle myokinase, papain).

Low temperatures do not destroy enzymes, but only suspend their action. The optimum temperature for the manifestation of enzyme activity is 37-40°C.

The activity of enzymes is influenced by the reaction of the medium. The pH value of the medium at which the enzyme exhibits maximum activity is called the optimum pH of the medium for the activity of this enzyme. The pH-optimum of the action of enzymes lies within the physiological range of 6.0-8.0. Exceptions: pepsin, the pH optimum of which is 2.0; arginase - the pH optimum is 10.0.

Enzymes are specific. There are several types of specificity:

1. Absolute specificity - the enzyme interacts with only one substrate. For example, urease accelerates the hydrolysis of urea, but does not cleave thiourea.

2. Stereospecificity - the enzyme interacts with a certain optical and geometric isomer.

3. Absolute group specificity - enzymes are specific in relation to the nature of the bond, as well as those compounds that form this bond. For example, α-amylase cleaves the α-glycosidic bond in the maltose molecule, which consists of two glucose molecules, but does not cleave the sucrose molecule, which consists of a glucose molecule and a fructose molecule.

4. Relative group specificity. In this case, the enzymes are specific only in relation to the bond, but are indifferent to those compounds that form this bond. For example, proteases accelerate the hydrolysis of peptide bonds in various proteins, lipases accelerate the cleavage of ester bonds in fats.

Question 19 Enzyme activators and inhibitors. The mechanism of their action. Reversible and irreversible, competitive and non-competitive inhibition. Using the principle of competitive inhibition in medicine.

.Activators and inhibitors of enzymes, mechanisms of their influence and significance.

The rate of chemical reactions is influenced by various substances. According to the nature of the influence, substances are divided into activators, which increase the activity of enzymes, and inhibitors (paralyzers), which suppress the activity of enzymes.

Enzyme activation can be caused by:

1. The presence of cofactors - metal ions Fe² +, Mg² +, Mn² +, Cu² +, Zn² +, ATP, lipoic acid.

2. Partial proteolysis.

Enzymes of the gastrointestinal tract are produced in the form of inactive forms - zymogens. Under influence various factors the cleavage of the peptide occurs with the formation of the active center and the zymogen turns into active form enzyme.

Pepsinogen HCl pepsin + peptide

Trypsinogen enterokinase trypsin + peptide

This type of activation prevents the cells of the gastrointestinal tract from self-digestion.

3. Phosphorylation and dephosphorylation. For example:

inactive lipase + ATP → lipase-phosphate (active lipase);

lipase-phosphate + H3PO4 → lipase (inactive lipase)

Inhibitors according to the nature of their action are divided into reversible and irreversible. This division is based on the strength of the inhibitor-enzyme bond.

Reversible inhibitors are compounds that interact non-covalently with an enzyme and can be cleaved from the enzyme.

Irreversible inhibitors are compounds that form covalent, strong bonds with an enzyme.

Irreversible inhibition can be specific and non-specific.

With specific inhibition, inhibitors inhibit the action of certain enzymes by binding individual functional groups active center. For example, thiol poisons inhibit enzymes whose active center includes SH groups; carbon monoxide (CO) inhibits enzymes that have Fe² + in the active center.

Nonspecific inhibitors inhibit the action of all enzymes. These include all denaturing factors ( heat, organic and mineral acids, salts heavy metals and etc.).

Reversible inhibition can be competitive. In this case, the inhibitor is a structural analogue of the substrate and competes with it for binding in the substrate-binding site of the active center.

Distinctive feature competitive inhibition is that it can be weakened or completely eliminated by increasing the concentration of the substrate.

Succinate dehydrogenase (SDH) is an enzyme of the citrate cycle that dehydrates succinate, converting it to fumarate. Malonate, which is structurally similar to succinate, binds to the active site of SDH but cannot be dehydrated. Therefore, malonate is a competitive inhibitor of SDH.

Many medications are competitive enzyme inhibitors. For example, sulfanilamide preparations, being structural analogues of para-aminobenzoic acid (PABA), the main growth factor of pathogenic microorganisms, compete with it for binding in the substrate-binding site of the active center of the enzyme. This is the basis of the antimicrobial action of sulfanilamide preparations.

the basis of all life processes make up thousands of chemical reactions catalyzed by enzymes. The significance of enzymes was accurately and figuratively determined by I.P. Pavlov, calling them "activators of life". Enzyme dysfunction leads to serious illnesses- phenylketonuria, glycogenosis, galactosemia, tyrosinemia or a significant decrease in the quality of life - dyslipoproteinemia, hemophilia.

It is known that for the implementation of a chemical reaction, it is necessary that the reacting substances have a total energy higher than the value called energy barrier reactions. To characterize the magnitude of the energy barrier, Arrhenius introduced the concept activation energy. Overcoming the activation energy in a chemical reaction is achieved either by increasing the energy of interacting molecules, for example, by heating, irradiating, increasing pressure, or by reducing the energy costs required for the reaction (i.e., activation energy) using catalysts.

Activation energy with and without enzyme

By their function, enzymes are biological catalysts. The essence of the action of enzymes, as well as inorganic catalysts, is:

• in the activation of molecules of reactants,
• in dividing the reaction into several stages, the energy barrier of each of which is lower than that of the overall reaction.

However, enzymes will not catalyze energetically impossible reactions; they accelerate only those reactions that can take place under given conditions.

Similarities and differences between enzymes and inorganic catalysts

The acceleration of reactions with the help of enzymes is very significant, for example:

A. Urease accelerates the reaction of decomposition of quite stable urea to ammonia and water by 10-13 times, therefore, with a urinary tract infection (appearance of bacterial urease), urine acquires an ammonia smell.

B. Consider the decomposition reaction of hydrogen peroxide:

2H 2 O 2 → O 2 + 2H 2 O

If the reaction rate without a catalyst is taken as unity, then in the presence of platinum black the reaction rate increases by 2 × 10 4 times and the activation energy decreases from 18 to 12 kcal / mol, in the presence of the catalase enzyme, the reaction rate increases by 2 × 10 11 times with energy activation 2 kcal/mol.

similarity
1. Catalyze only energetically possible reactions. 2. Do not change the direction of the reaction. 3. Accelerate the onset of reaction equilibrium, but do not shift it. 4. Not consumed in the reaction process.	1. The speed of the enzymatic reaction is much higher. 2. High specificity. 3. Soft working conditions (intracellular). 4. Ability to control the reaction rate. 5. The rate of the enzymatic reaction is proportional to the amount of the enzyme.

Enzymatic catalysis has its own characteristics

Stages of catalysis

In an enzymatic reaction, the following stages can be distinguished:

1. Attachment of a substrate (S) to an enzyme (E) to form an enzyme-substrate complex (E-S).

2. Transformation of the enzyme-substrate complex into one or more transition complexes (E-X) in one or more steps.

3. Conversion of the transition complex to an enzyme-product complex (E-P).

4. Separation of end products from the enzyme.

Mechanisms of catalysis

Donors	Acceptors
COOH -NH 3 + -SH	COO- -NH 2 -S-

1. Acid-base catalysis– in the active center of the enzyme there are groups of specific amino acid residues that are good donors or acceptors of protons. Such groups are powerful catalysts for many organic reactions.

2. covalent catalysis- Enzymes react with their substrates, forming very unstable enzyme-substrate complexes with the help of covalent bonds, from which reaction products are formed during intramolecular rearrangements.

Types of enzymatic reactions

1. Ping pong type- the enzyme first interacts with substrate A, taking away from it any chemical groups and turning into the corresponding product. Substrate B is then attached to the enzyme, receiving these chemical groups. An example is the transfer of amino groups from amino acids to keto acids - transamination.

Enzymatic reaction like "ping-pong"

2. Type of sequential reactions– Substrates A and B are sequentially added to the enzyme, forming a "triple complex", after which catalysis occurs. The reaction products are also sequentially cleaved off from the enzyme.

Enzymatic reaction according to the type of "successive reactions"

3. Type of random interactions– substrates A and B are attached to the enzyme in any order, randomly, and after catalysis they are also cleaved off.

Enzymatic reaction according to the type of "random interactions"

Enzymes are proteins

It has long been found that all enzymes are proteins and have all the properties of proteins. Therefore, like proteins, enzymes are divided into simple and complex.

simple enzymes are made up of only amino acids, for example, pepsin , trypsin , lysozyme.

Complex enzymes(holoenzymes) have in their composition a protein part consisting of amino acids - apoenzyme, and the non-protein part - cofactor. The cofactor, in turn, can be called coenzyme or prosthetic group. An example might be succinate dehydrogenase (contains FAD) (in the tricarboxylic acid cycle), aminotransferases (contain pyridoxal phosphate) (function), peroxidase(contains heme). For the implementation of catalysis, a full-fledged complex of apoprotein and cofactor is required; they cannot catalyze separately.

Like many proteins, enzymes can be monomers, i.e. consist of one subunit, and polymers consisting of several subunits.

Comparison of inorganic enzyme catalysts Signs of comparison Inorganic catalysts Enzymes 1. Chemical nature 2. Selectivity 3. Optimum pH 4. Temperature ranges 5. Changes in the structure of kat during the reaction 6. Increasing the reaction rate.

Comparison of inorganic enzyme catalysts Signs of comparison Inorganic catalysts Enzymes 1. Chemical nature Low molecular weight substances formed by 1 or several elements. Proteins - high molecular weight polymers 2. Selectivity Low, universal kat - Pt accelerates multiplier. reactions. High. Each district needs its own enzyme. 3. Optimum pH Strongly acidic or alkaline Small range, each. organ - his own. 4. Temperature ranges Very wide. 35 - 42 degrees, then denatured. 5. Changes in the structure of kat during the reaction Changes slightly, or does not change at all. They change strongly and are restored to the original structure at the end of the reaction. 6. Increasing the reaction rate. 100 - times From 10 to the 8th power to 10 to the 12th power of times.

General: capable of dissolving in water and forming colloidal solutions; increase the rate of reaction; are not consumed in the reaction; amphoteric; their presence does not affect the properties of the reaction products; the flow of color reactions is characteristic; change the activation energy at which the reaction can occur; do not significantly change the temperature at which the reaction occurs; capable of denaturation and hydrolysis.

Specific: Combination highest activity subject to a strict set of conditions; The specificity of the action on the principle of "key - lock" or "hand - glove"; Stability; Reversibility of action: E + S ES E + P, where E is an enzyme; S—substrate, P—reaction product, ES—enzyme-substrate complex.

The role of enzymes in the vital activity of organisms: Congenital metabolic disorders; Interconversions of substances; biochemical revolution; Energy transformation; Biosynthesis; Pharmacology; membrane ultrastructure; genetic apparatus; Nutrition; Cellular metabolism; Catalysis; Physiological regulation; bacterial fermentation.