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Enzymes are organic substances. Biochemistry of enzymes




Enzymes are a special type of proteins that nature has assigned the role of catalysts for various chemical processes.

This term is constantly heard, however, not everyone understands what an enzyme or enzyme is, what functions this substance performs, and how enzymes differ from enzymes and whether they differ at all. We'll find out all this now.

Without these substances, neither humans nor animals would be able to digest food. And for the first time, mankind resorted to the use of enzymes in everyday life more than 5 thousand years ago, when our ancestors learned to store milk in "dishes" from the stomachs of animals. Under such conditions, under the influence of rennet, it turned into cheese. And this is just one example of how an enzyme works as a catalyst that speeds up biological processes. Today, enzymes are indispensable in industry, they are important for the production of leather, textiles, alcohol and even concrete. These beneficial substances are also present in detergents and washing powders - they help remove stains at low temperatures.

Discovery history

Enzyme in Greek means "sourdough". And mankind owes the discovery of this substance to the Dutchman Jan Baptist Van Helmont, who lived in the 16th century. At one time he became very interested in alcoholic fermentation and during the study he found an unknown substance that accelerates this process. The Dutchman called it fermentum, which means fermentation. Then, almost three centuries later, the Frenchman Louis Pasteur, also observing fermentation processes, came to the conclusion that enzymes are nothing but the substances of a living cell. And after some time, the German Eduard Buchner extracted the enzyme from yeast and determined that this substance is not a living organism. He also gave him his name - "zimaza". A few years later, another German, Willy Kuehne, proposed to divide all protein catalysts into two groups: enzymes and enzymes. Moreover, he proposed to call the second term “sourdough”, the actions of which extend outside living organisms. And only 1897 put an end to all scientific disputes: it was decided to use both terms (enzyme and enzyme) as absolute synonyms.

Structure: a chain of thousands of amino acids

All enzymes are proteins, but not all proteins are enzymes. Like other proteins, enzymes are made up of . And interestingly, the creation of each enzyme takes from a hundred to a million amino acids strung like pearls on a string. But this thread is not even - it is usually bent hundreds of times. Thus, a three-dimensional structure unique for each enzyme is created. Meanwhile, the enzyme molecule is a relatively large formation, and only a small part of its structure, the so-called active center, is involved in biochemical reactions.

Each amino acid is connected to a specific type of chemical bond, and each enzyme has its own unique amino acid sequence. To create most of them, about 20 types are used. Even minor changes in the amino acid sequence can dramatically change the look and feel of an enzyme.

Biochemical properties

Although a huge number of reactions occur in nature with the participation of enzymes, they can all be divided into 6 categories. Accordingly, each of these six reactions proceeds under the influence of a certain type of enzyme.

Reactions involving enzymes:

  1. Oxidation and reduction.

The enzymes involved in these reactions are called oxidoreductases. As an example, remember how alcohol dehydrogenases convert primary alcohols to aldehyde.

  1. Group transfer reaction.

The enzymes responsible for these reactions are called transferases. They have the ability to move functional groups from one molecule to another. This happens, for example, when alanine aminotransferases move alpha-amino groups between alanine and aspartate. Transferases also move phosphate groups between ATP and other compounds, and create them from residues.

  1. Hydrolysis.

The hydrolases involved in the reaction are able to break single bonds by adding elements of water.

  1. Create or remove a double bond.

This type of reaction occurs in a non-hydrolytic way with the participation of lyase.

  1. Isomerization of functional groups.

In many chemical reactions, the position of the functional group changes within the molecule, but the molecule itself is made up of the same number and types of atoms as it was before the reaction began. In other words, the substrate and product of the reaction are isomers. This type of transformation is possible under the influence of isomerase enzymes.

  1. The formation of a single bond with the elimination of the element water.

Hydrolases break bonds by adding water elements to the molecule. Lyases carry out the reverse reaction, removing the aqueous part from the functional groups. Thus, a simple connection is created.

How they work in the body

Enzymes speed up almost all chemical reactions that occur in cells. They are vital for humans, facilitate digestion and speed up metabolism.

Some of these substances help break down molecules that are too large into smaller "chunks" that the body can digest. Others, on the contrary, bind small molecules. But enzymes, scientifically speaking, are highly selective. This means that each of these substances is capable of accelerating only a certain reaction. The molecules that enzymes work with are called substrates. The substrates, in turn, form a bond with a part of the enzyme called the active site.

There are two principles that explain the specifics of the interaction of enzymes and substrates. In the so-called "key-lock" model, the active site of the enzyme occupies the place of a strictly defined configuration in the substrate. According to another model, both participants in the reaction, the active site and the substrate, change their shapes in order to connect.

Whatever the principle of the interaction, the result is always the same - the reaction under the influence of the enzyme proceeds many times faster. As a result of this interaction, new molecules are “born”, which are then separated from the enzyme. And the catalyst substance continues to do its job, but with the participation of other particles.

Hyper- and hypoactivity

There are times when enzymes perform their functions with the wrong intensity. Excessive activity causes excessive reaction product formation and substrate deficiency. The result is poor health and serious illness. The cause of enzyme hyperactivity can be either a genetic disorder or an excess of vitamins or used in the reaction.

Enzyme hypoactivity can even cause death when, for example, enzymes do not remove toxins from the body or ATP deficiency occurs. The cause of this condition can also be mutated genes or, conversely, hypovitaminosis and a deficiency of other nutrients. In addition, lower body temperature similarly slows down the functioning of enzymes.

Catalyst and more

Today you can often hear about the benefits of enzymes. But what are these substances on which the performance of our body depends?

Enzymes are biological molecules whose life cycle is not determined by the boundaries of birth and death. They just work in the body until they dissolve. As a rule, this occurs under the influence of other enzymes.

In the course of a biochemical reaction, they do not become part of the final product. When the reaction is complete, the enzyme leaves the substrate. After that, the substance is ready to start working again, but on a different molecule. And so it goes on for as long as the body needs.

The uniqueness of enzymes is that each of them performs only one assigned function. A biological reaction occurs only when the enzyme finds the right substrate for it. This interaction can be compared with the principle of operation of a key and a lock - only correctly selected elements can work together. Another feature: they can work at low temperatures and moderate pH, and as catalysts they are more stable than any other chemicals.

Enzymes as catalysts speed up metabolic processes and other reactions.

As a rule, these processes consist of certain stages, each of which requires the work of a certain enzyme. Without this, the transformation or acceleration cycle cannot be completed.

Perhaps the most well-known of all the functions of enzymes is the role of a catalyst. This means that enzymes combine chemicals in such a way as to reduce the energy costs required to form a product more quickly. Without these substances, chemical reactions would proceed hundreds of times slower. But the abilities of enzymes do not end there. All living organisms contain the energy they need to continue living. Adenosine triphosphate, or ATP, is a kind of charged battery that supplies energy to cells. But the functioning of ATP is impossible without enzymes. And the main enzyme that produces ATP is synthase. For each glucose molecule that is converted into energy, synthase produces about 32-34 ATP molecules.

In addition, enzymes (lipase, amylase, protease) are actively used in medicine. In particular, they serve as a component of enzymatic preparations, such as Festal, Mezim, Panzinorm, Pancreatin, used to treat indigestion. But some enzymes can also affect the circulatory system (dissolve blood clots), accelerate the healing of purulent wounds. And even in anti-cancer therapy, they also resort to the help of enzymes.

Factors that determine the activity of enzymes

Since the enzyme is able to speed up reactions many times over, its activity is determined by the so-called turnover number. This term refers to the number of substrate molecules (reactive substances) that 1 enzyme molecule can transform in 1 minute. However, there are a number of factors that determine the rate of a reaction:

  1. substrate concentration.

Increasing the substrate concentration leads to an acceleration of the reaction. The more molecules of the active substance, the faster the reaction proceeds, since more active centers are involved. However, acceleration is possible only until all enzyme molecules are involved. After that, even increasing the concentration of the substrate will not accelerate the reaction.

  1. Temperature.

Usually, an increase in temperature leads to an acceleration of reactions. This rule works for most enzymatic reactions, but only as long as the temperature does not rise above 40 degrees Celsius. After this mark, the reaction rate, on the contrary, begins to decrease sharply. If the temperature drops below a critical point, the rate of enzymatic reactions will increase again. If the temperature continues to rise, the covalent bonds are broken and the catalytic activity of the enzyme is lost forever.

  1. Acidity.

The rate of enzymatic reactions is also affected by the pH value. Each enzyme has its own optimal level of acidity, at which the reaction proceeds most adequately. Changing the pH level affects the activity of the enzyme, and hence the rate of the reaction. If the change is too great, the substrate loses its ability to bind to the active nucleus, and the enzyme can no longer catalyze the reaction. With the restoration of the required pH level, the activity of the enzyme is also restored.

Enzymes present in the human body can be divided into 2 groups:

  • metabolic;
  • digestive.

Metabolic "work" to neutralize toxic substances, and also contribute to the production of energy and proteins. And, of course, they accelerate the biochemical processes in the body.

What the digestive organs are responsible for is clear from the name. But even here the principle of selectivity works: a certain type of enzyme affects only one type of food. Therefore, to improve digestion, you can resort to a little trick. If the body does not digest something from food well, then it is necessary to supplement the diet with a product containing an enzyme that can break down hard-to-digest food.

Food enzymes are catalysts that break down food to a state in which the body is able to absorb useful substances from them. Digestive enzymes come in several types. In the human body, different types of enzymes are found in different parts of the digestive tract.

Oral cavity

At this stage, alpha-amylase acts on the food. It breaks down carbohydrates, starches and glucose found in potatoes, fruits, vegetables and other foods.

Stomach

Here, pepsin breaks down proteins into peptides, and gelatinase breaks down the gelatin and collagen found in meat.

Pancreas

At this stage, "work":

  • trypsin - responsible for the breakdown of proteins;
  • alpha-chymotrypsin - helps the absorption of proteins;
  • elastase - break down certain types of proteins;
  • nucleases - help break down nucleic acids;
  • steapsin - promotes the absorption of fatty foods;
  • amylase - responsible for the absorption of starches;
  • lipase - breaks down fats (lipids) found in dairy products, nuts, oils, and meats.

Small intestine

Over food particles "conjure":

  • peptidases - break down peptide compounds to the level of amino acids;
  • sucrase - helps to absorb complex sugars and starches;
  • maltase - breaks down disaccharides to the state of monosaccharides (malt sugar);
  • lactase - breaks down lactose (glucose found in dairy products);
  • lipase - promotes the absorption of triglycerides, fatty acids;
  • erepsin - affects proteins;
  • isomaltase - "works" with maltose and isomaltose.

Colon

Here the functions of enzymes are performed:

  • coli - responsible for digestion;
  • lactobacilli - affect lactose and some other carbohydrates.

In addition to these enzymes, there are also:

  • diastase - digests vegetable starch;
  • invertase - breaks down sucrose (table sugar);
  • glucoamylase - converts to glucose;
  • alpha-galactosidase - promotes the digestion of beans, seeds, soy products, root vegetables and leafy vegetables;
  • bromelain - an enzyme derived from, promotes the breakdown of different types of proteins, is effective at different levels of acidity of the environment, and has anti-inflammatory properties;
  • papain, an enzyme isolated from raw papaya, promotes the breakdown of small and large proteins, and is effective over a wide range of substrates and acidity.
  • cellulase - breaks down cellulose, plant fibers (not found in the human body);
  • endoprotease - cleaves peptide bonds;
  • ox bile extract - an enzyme of animal origin, stimulates intestinal motility;
  • pancreatin - an enzyme of animal origin, accelerates the digestion of proteins;
  • pancrelipase - an animal enzyme that promotes the absorption

    Fermented foods are a near-perfect source of beneficial bacteria needed for proper digestion. And while pharmacy probiotics "work" only in the upper digestive system and often do not reach the intestines, the effect of enzymatic products is felt throughout the gastrointestinal tract.

    For example, apricots contain a mixture of beneficial enzymes, including invertase, which is responsible for the breakdown of glucose and promotes rapid energy release.

    A natural source of lipase (promotes faster digestion of lipids) can serve. In the body, this substance is produced by the pancreas. But in order to make life easier for this body, you can treat yourself, for example, to a salad with avocado - tasty and healthy.

    In addition to being perhaps the most famous source, it also supplies amylase and maltase to the body. Amylase is also found in bread and cereals. Maltase aids in the breakdown of maltose, the so-called malt sugar, which is abundant in beer and corn syrup.

    Another exotic fruit - pineapple contains a whole range of enzymes, including bromelain. And it, according to some studies, also has anti-cancer and anti-inflammatory properties.

    Extremophiles and industry

    Extremophiles are substances that can survive in extreme conditions.

    Living organisms, as well as the enzymes that enable them to function, have been found in geysers where the temperature is close to the boiling point, and deep in ice, as well as in conditions of extreme salinity (Death Valley in the USA). In addition, scientists have found enzymes for which the pH level, as it turned out, is also not a fundamental requirement for effective work. Researchers are studying extremophile enzymes with particular interest as substances that can be widely used in industry. Although even today enzymes have already found their application in the industry as biologically and environmentally friendly substances. The use of enzymes is resorted to in the food industry, cosmetology, and the production of household chemicals.

    Izvozchikova Nina Vladislavovna

    Speciality: infectious disease specialist, gastroenterologist, pulmonologist.

    General experience: 35 years .

    Education:1975-1982, 1MMI, San-Gig, highest qualification, infectious diseases doctor.

    Science degree: doctor of the highest category, candidate of medical sciences.

8.7.1. In the cellular content, enzymes are not distributed randomly, but strictly ordered. With the help of intracellular membranes, the cell is divided into compartments or compartments(Figure 8.18). Strictly defined biochemical processes are carried out in each of them and the corresponding enzymes or polyenzymatic complexes are concentrated. Here are some typical examples.

Figure 8.18. Intracellular distribution of enzymes of various metabolic pathways.

Lysosomes contain predominantly a variety of hydrolytic enzymes. Here, the processes of splitting complex organic compounds into their structural components take place.

Mitochondria contain complex systems of redox enzymes.

Enzymes for activating amino acids are distributed in the hyaloplasm, but they are also present in the nucleus. The hyaloplasm contains numerous metabolons of glycolysis, structurally combined with those of the pentose phosphate cycle, which ensures the relationship between the dichotomous and apotomic pathways of carbohydrate breakdown.

At the same time, enzymes that accelerate the transfer of amino acid residues to the growing end of the polypeptide chain and catalyze some other reactions in the process of protein biosynthesis are concentrated in the ribosomal apparatus of the cell.

In the cell nucleus, mainly nucleotidyltransferases are localized, accelerating the transfer of nucleotide residues during the formation of nucleic acids.

8.7.2. The distribution of enzymes in subcellular organelles is studied after preliminary fractionation of cell homogenates by high-speed centrifugation, determining the content of enzymes in each fraction.

The localization of a given enzyme in a tissue or cell can often be established in situ by histochemical methods ("histoenzymology"). To do this, thin (from 2 to 10 µm) sections of frozen tissue are treated with a solution of a substrate to which this enzyme is specific. In those places where the enzyme is located, the product of the reaction catalyzed by this enzyme is formed. If the product is colored and insoluble, it remains at the site of formation and allows the localization of the enzyme. Histoenzymology provides a clear and, to a certain extent, physiological picture of the distribution of enzymes.

Enzyme systems of enzymes concentrated in intracellular structures are finely coordinated with each other. The interconnection of the reactions catalyzed by them ensures the vital activity of cells, organs, tissues and the organism as a whole.

When studying the activity of various enzymes in the tissues of a healthy body, one can get a picture of their distribution. It turns out that some enzymes are widely distributed in many tissues, but at different concentrations, while others are very active in extracts obtained from one or more tissues, and are practically absent in other tissues of the body.

Figure 8.19. The relative activity of certain enzymes in human tissues, expressed as a percentage of the activity in the tissue with the maximum concentration of this enzyme (Moss, Butterworth, 1978).

8.7.3. The concept of enzymopathies. In 1908, the English physician Archibald Garrod suggested that the cause of a number of diseases may be the absence of any of the key enzymes involved in metabolism. He introduced the concept of "inborn errors of metabolism" (congenital defect of metabolism). Subsequently, this theory was confirmed by new data obtained in the field of molecular biology and pathological biochemistry.

Information about the sequence of amino acids in the polypeptide chain of a protein is recorded in the corresponding section of the DNA molecule in the form of a sequence of trinucleotide fragments - triplets or codons. Each triplet codes for a specific amino acid. This correspondence is called the genetic code. Moreover, some amino acids can be encoded with several codons. There are also special codons that are signals for the start of the synthesis of the polypeptide chain and its termination. To date, the genetic code has been completely deciphered. It is universal for all kinds of living organisms.

The realization of the information contained in the DNA molecule includes several stages. First, messenger RNA (mRNA) is synthesized in the cell nucleus during transcription and enters the cytoplasm. In turn, mRNA serves as a template for translation - the synthesis of polypeptide chains on ribosomes. Thus, the nature of molecular diseases is determined by the disruption of the structure and function of nucleic acids and the proteins controlled by them.

8.7.4. Since information about the structure of all proteins in a cell is contained in the sequence of DNA nucleotides, and each amino acid is determined by a triplet of nucleotides, a change in the primary structure of DNA can ultimately have a profound effect on the synthesized protein. Such changes occur due to errors in DNA replication, when one nitrogenous base is replaced by another, either as a result of radiation or chemical modification. All inherited defects that have arisen in this way are called mutations. They can lead to misreading of the code and deletion (loss) of a key amino acid, substitution of one amino acid for another, premature cessation of protein synthesis, or addition of amino acid sequences. Taking into account the dependence of the spatial packing of a protein on the linear sequence of amino acids in it, it can be assumed that such defects can change the structure of the protein, and hence its function. However, many mutations are only found in the laboratory and do not adversely affect protein function. Thus, the key point is the localization of changes in the primary structure. If the position of the replaced amino acid is critical for the formation of the tertiary structure and the formation of the catalytic site of the enzyme, then the mutation is serious and may manifest as a disease.

The consequences of a deficiency of one enzyme in the chain of metabolic reactions can manifest themselves in different ways. We assume that the transformation of the compound A into the connection B catalyzes an enzyme E and what connection C occurs on an alternative transformation path (Figure 8.20):

Figure 8.20. Scheme of alternative ways of biochemical transformations.

The consequences of enzyme deficiency can be the following phenomena:

  1. insufficiency of the product of the enzymatic reaction ( B). As an example, we can point to a decrease in blood glucose in some forms of glycogenosis;
  2. accumulation of matter A), the conversion of which is catalyzed by an enzyme (for example, homogentisic acid in alkaptonuria). In many lysosomal storage diseases, substances that normally undergo hydrolysis in lysosomes accumulate in them due to a deficiency of one of the enzymes;
  3. deviation to an alternative path with the formation of some biologically active compounds ( C). This group of phenomena includes urinary excretion of phenylpyruvic and phenyllactic acids, which are formed in the body of patients with phenylketonuria as a result of activation of auxiliary pathways for the breakdown of phenylalanine.

If metabolic conversion as a whole is regulated by the end product feedback principle, then the effects of the last two types of anomalies will be more significant. So, for example, in porphyrias (congenital disorders of heme synthesis), the overwhelming effect of heme on the initial synthesis reactions is eliminated, which leads to the formation of excessive amounts of intermediate products of the metabolic pathway, which have a toxic effect on the cells of the skin and nervous system.

Environmental factors may enhance or even completely determine the clinical manifestations of some congenital metabolic disorders. For example, many patients with glucose-6-phosphate dehydrogenase deficiency do not develop disease until after taking drugs such as primaquine. In the absence of contact with drugs, such people give the impression of being healthy.

8.7.5. Enzyme deficiency is usually judged indirectly by an increase in the concentration of the starting substance, which normally undergoes transformations under the action of this enzyme (for example, phenylalanine in phenylketonuria). Direct determination of the activity of such enzymes is carried out only in specialized centers, but if possible, the diagnosis should be confirmed by this method. Prenatal (antenatal) diagnosis of some congenital metabolic disorders is possible by examining amniotic fluid cells obtained in the early stages of pregnancy and cultured in vitro.

Some congenital metabolic disorders can be treated by delivering the missing metabolite to the body or by limiting the intake of precursors of impaired metabolic processes into the gastrointestinal tract. Accumulating products (eg, iron in hemochromatosis) can sometimes be removed.

Digestive enzymes- These are substances of a protein nature that are produced in the gastrointestinal tract. They provide the process of digestion of food and stimulate its assimilation.

The main function of digestive enzymes is the decomposition of complex substances into simpler ones that are easily absorbed in the human intestine.

The action of protein molecules is directed to the following groups of substances:

  • proteins and peptides;
  • oligo- and polysaccharides;
  • fats, lipids;
  • nucleotides.

Types of enzymes

  1. Pepsin. An enzyme is a substance that is produced in the stomach. It acts on the protein molecules in the composition of food, decomposing them into elementary components - amino acids.
  2. Trypsin and chymotrypsin. These substances are part of the group of pancreatic enzymes that are produced by the pancreas and delivered to the duodenum. Here they also act on protein molecules.
  3. Amylase. The enzyme refers to substances that decompose sugars (carbohydrates). Amylase is produced in the mouth and in the small intestine. It decomposes one of the main polysaccharides - starch. The result is a small carbohydrate called maltose.
  4. Maltase. The enzyme also acts on carbohydrates. Its specific substrate is maltose. It decomposes into 2 glucose molecules, which are absorbed by the intestinal wall.
  5. Sucrase. Protein acts on another common disaccharide, sucrose, which is found in any high-carbohydrate food. Carbohydrate breaks down into fructose and glucose, which are easily absorbed by the body.
  6. Lactase. A specific enzyme that acts on the carbohydrate from milk is lactose. When it decomposes, other products are obtained - glucose and galactose.
  7. Nucleases. Enzymes from this group act on nucleic acids - DNA and RNA, which are found in food. After their impact, the substances break down into separate components - nucleotides.
  8. Nucleotidase. The second group of enzymes that act on nucleic acids are called nucleotidases. They decompose nucleotides into smaller components - nucleosides.
  9. Carboxypeptidase. The enzyme acts on small protein molecules - peptides. As a result of this process, individual amino acids are obtained.
  10. Lipase. The substance decomposes fats and lipids entering the digestive system. In this case, their constituent parts are formed - alcohol, glycerin and fatty acids.

Lack of digestive enzymes

Insufficient production of digestive enzymes is a serious problem that requires medical intervention. With a small amount of endogenous enzymes, food cannot be digested normally in the human intestine.

If the substances are not digested, then they cannot be absorbed in the intestines. The digestive system is able to assimilate only small fragments of organic molecules. Large components that are part of food will not be able to benefit a person. As a result, the body may develop a deficiency of certain substances.

Lack of carbohydrates or fats will lead to the fact that the body will lose the "fuel" for vigorous activity. Protein deficiency deprives the human body of building material, which are amino acids. In addition, indigestion leads to a change in the nature of the feces, which can adversely affect the character.

The reasons

  • inflammatory processes in the intestines and stomach;
  • eating disorders (overeating, insufficient heat treatment);
  • metabolic diseases;
  • pancreatitis and other diseases of the pancreas;
  • damage to the liver and biliary tract;
  • congenital pathologies of the enzyme system;
  • postoperative consequences (insufficiency of enzymes due to the removal of part of the digestive system);
  • medicinal effects on the stomach and intestines;
  • pregnancy;

Symptoms

Long-term preservation of insufficiency of digestion is accompanied by the appearance of general symptoms associated with a reduced intake of nutrients in the body. This group includes the following clinical manifestations:

  • general weakness;
  • decrease in working capacity;
  • headaches;
  • sleep disorders;
  • increased irritability;
  • in severe cases, symptoms of anemia due to insufficient absorption of iron.

Excess digestive enzymes

An excess of digestive enzymes is most commonly seen in conditions such as pancreatitis. The condition is associated with hyperproduction of these substances by pancreatic cells and a violation of their excretion into the intestine. In this regard, active inflammation develops in the tissue of the organ, caused by the action of enzymes.

Signs of pancreatitis may include:

  • severe pain in the abdomen;
  • nausea;
  • bloating;
  • violation of the nature of the chair.

Often a general deterioration in the patient's condition develops. General weakness, irritability appear, body weight decreases, normal sleep is disturbed.

How to detect violations in the synthesis of digestive enzymes?

Basic principles of therapy for enzyme disorders

A change in the production of digestive enzymes is a reason to see a doctor. After a comprehensive examination, the doctor will determine the cause of the violations and prescribe the appropriate treatment. It is not recommended to deal with pathology on your own.

An important component of treatment is proper nutrition. The patient is prescribed an appropriate diet, which is aimed at facilitating the digestion of food. Overeating should be avoided, as this provokes intestinal disorders. Patients are prescribed drug therapy, including substitution treatment.

Specific means and their dosages are selected by the doctor.

Enzymes are globular proteins that help all cellular processes to run. Like all catalysts, they cannot reverse the reaction, but serve to speed it up.

Localization of enzymes in the cell

Inside the cell, individual enzymes are usually contained and act in well-defined organelles. The localization of enzymes is directly related to the function that this part of the cell usually performs.

Almost all glycolytic enzymes are located in the cytoplasm. Enzymes of the tricarboxylic acid cycle - in the mitochondrial matrix. Active substances of hydrolysis are contained in lysosomes.

Separate tissues and organs of animals and plants differ not only in the set of enzymes, but also in their activity. This feature of tissues is used in the clinic in the diagnosis of certain diseases.

There are also age-related features in the activity and set of enzymes in tissues. They are most clearly seen during embryonic development during tissue differentiation.

Enzyme nomenclature

There are several naming systems, each of which takes into account the properties of enzymes to a different extent.

  • Trivial. The names of substances are given randomly. For example, pepsin (pepsis - "digestion", Greek) and trypsin (tripsis - "thinn", Greek)
  • Rational. The name of the enzyme consists of the substrate and the ending "-ase". For example, amylase accelerates (amylo - "starch", Greek).
  • Moscow. It was adopted in 1961 by the International Commission on Enzyme Nomenclature at the 5th International Congress of Biochemistry. The name of the substance is made up of the substrate and the reaction that is catalyzed (accelerated) by the enzyme. If the function of enzymes is to transfer a group of atoms from one molecule (substrate) to another (acceptor), the name of the catalyst includes the chemical name of the acceptor. For example, in the reaction of transferring an amino group from alanine to 2-hydroxyglutaric acid, the enzyme alanine: 2-oxoglutarate aminotransferase is involved. The name reflects:
    • substrate - alanine;
    • acceptor - 2-oxoglutaric acid;
    • the amino group is transferred in the reaction.

The International Commission has compiled a list of all known enzymes, which is constantly updated. This is due to the discovery of new substances.

Enzyme classification

Enzymes can be divided into groups in two ways. The first offers two classes of these substances:

  • simple - consist only of protein;
  • complex - contain a protein part (apoenzyme) and a non-protein part, called a coenzyme.

Vitamins can be included in the non-protein part of a complex enzyme. Interaction with other substances occurs through the active center. The whole enzyme molecule does not take part in the process.

The properties of enzymes, like other proteins, are determined by their structure. Depending on it, catalysts accelerate only their reactions.

The second classification method divides substances according to the function of enzymes. The result is six classes:

  • oxidoreductases;
  • transferases;
  • hydrolases;
  • isomerases;
  • lyases;
  • ligases.

These are generally accepted groups, they differ not only in the types of reactions that regulate the enzymes they contain. Substances of different groups have different structures. And the functions of enzymes in a cell, therefore, cannot be the same.

Oxidoreductases - redox

The main function of the enzymes of the first group is the acceleration of redox reactions. A characteristic feature: the ability to form chains of oxidative enzymes, in which electrons or hydrogen atoms are transferred from the very first substrate to the final acceptor. These substances are separated according to the principle of work or the place of work in the reaction.

  1. Aerobic dehydrogenases (oxidases) accelerate the transfer of electrons or protons directly to oxygen atoms. Anaerobic ones perform the same actions, but in reactions that proceed without the transfer of electrons or hydrogen atoms to oxygen atoms.
  2. Primary dehydrogenases catalyze the process of removing hydrogen atoms from the oxidized substance (primary substrate). Secondary - accelerate the removal of hydrogen atoms from the secondary substrate, they were obtained using primary dehydrogenase.

Another feature: being two-component catalysts with a very limited set of coenzymes (active groups), they can accelerate a wide variety of redox reactions. This is achieved by a large number of options: the same coenzyme can join different apoenzymes. In each case, a special oxidoreductase is obtained with its own properties.

There is another function of the enzymes of this group, which cannot be ignored - they accelerate the course of chemical processes associated with the release of energy. Such reactions are called exothermic.

Transferases - carriers

These enzymes perform the function of accelerating the transfer reactions of molecular residues and functional groups. For example, phosphofructokinase.

There are eight groups of catalysts based on the transferred group. Let's consider only some of them.

  1. Phosphotransferases - help carry residues They are divided into subclasses according to the destination (alcohol, carboxyl and others).
  2. Aminotransferases - speed up reactions
  3. Glycosyltransferases - transfer glycosyl residues from phosphate ester molecules to mono- and polysaccharide molecules. Provide reactions of decomposition and synthesis of oligo- or polysaccharides in organisms of plants and animals. For example, they are involved in the breakdown of sucrose.
  4. Acyltransferases transfer carboxylic acid residues to amines, alcohols, and amino acids. Acyl-coenzyme-A is a universal source of acyl groups. It can be considered as an active group of acyltransferases. Acyl acetic acid is most commonly tolerated.

Hydrolases - break down with the participation of water

In this group, enzymes act as catalysts for the reactions of splitting (less often synthesis) of organic compounds in which water is involved. Substances of this group are contained in the cells and in the digestive juice. Molecules of catalysts in the gastrointestinal tract consist of one component.

The site of localization of these enzymes are lysosomes. They perform the protective functions of enzymes in the cell: they break down foreign substances that have passed through the membrane. They also destroy those substances that are no longer needed by the cell, for which lysosomes were nicknamed orderlies.

Their other "nickname" is cell suicides, as they are the main tool for cell autolysis. If an infection occurs, inflammatory processes begin, the lysosome membrane becomes permeable and hydrolases enter the cytoplasm, destroying everything in its path and destroying the cell.

There are several types of catalysts from this group:

  • esterases - are responsible for the hydrolysis of esters of alcohols;
  • glycosidases - accelerate the hydrolysis of glycosides, depending on which isomer they act on, secrete α- or β-glycosidases;
  • peptide hydrolases - are responsible for the hydrolysis of peptide bonds in proteins, and under certain conditions for their synthesis, but this method of protein synthesis is not used in a living cell;
  • amidases - are responsible for the hydrolysis of acid amides, for example, urease catalyzes the breakdown of urea into ammonia and water.

Isomerases - transformation of a molecule

These substances accelerate changes within a single molecule. They can be geometric or structural. This can happen in many ways:

  • transfer of hydrogen atoms;
  • movement of the phosphate group;
  • change in the location of atomic groups in space;
  • movement of the double bond.

Isomerization can be organic acids, carbohydrates or amino acids. Isomerases can convert aldehydes to ketones and, conversely, rearrange the cis form to the trans form and vice versa. To better understand what function the enzymes of this group perform, it is necessary to know the differences in isomers.

Liases cut ties

These enzymes accelerate the non-hydrolytic decomposition of organic compounds along the bonds:

  • carbon-carbon;
  • phosphorus-oxygen;
  • carbon-sulfur;
  • carbon-nitrogen;
  • carbon-oxygen.

In this case, such simple products as water, ammonia are released, and double bonds are closed. Few of these reactions can go in the opposite direction; the corresponding enzymes, under suitable conditions, catalyze the processes of not only decay, but also synthesis.

Lyases are classified according to the type of bond they break. They are complex enzymes.

Ligases crosslink

The main function of the enzymes of this group is the acceleration of synthesis reactions. Their feature is the conjugation of the creation with the decay of substances that are able to provide energy for the implementation of the biosynthetic process. There are six subclasses according to the type of connection formed. Five of them are identical to the lyase subgroups, and the sixth is responsible for creating the nitrogen-metal bond.

Some ligases are involved in particularly important cell processes. For example, DNA ligase is involved in the replication of deoxyribonucleic acid. It crosslinks single-strand breaks, creating new phosphodiester bonds. It is she who connects the Okazaki fragments.

The same enzyme is actively used in genetic engineering. It allows scientists to stitch together from the pieces they need, creating unique chains of deoxyribonucleic acid. Any information can be put into them, thus creating a factory for the production of the necessary proteins. For example, you can sew into the DNA of a bacterium a piece that is responsible for the synthesis of insulin. And when the cell will translate its own proteins, at the same time it will make a useful substance necessary for medical purposes. It remains only to be cleansed, and it will help many sick people.

The huge role of enzymes in the body

They can increase more than ten times. It is simply necessary for the normal functioning of the cell. And enzymes are involved in every reaction. Therefore, the functions of enzymes in the body are diverse, like all ongoing processes. And the failure of these catalysts leads to serious consequences.

Enzymes are widely used in food, light industry, medicine: they are used to make cheeses, sausages, canned food, they are also used in the manufacture of photographic materials.

ENZYMES, organic substances of protein nature, which are synthesized in cells and many times accelerate the reactions occurring in them, without undergoing chemical transformations. Substances that have a similar effect exist in inanimate nature and are called catalysts.

Enzymes (from Latin fermentum - fermentation, leaven) are sometimes called enzymes (from Greek en - inside, zyme - leaven). All living cells contain a very large set of enzymes, on the catalytic activity of which the functioning of cells depends. Almost each of the many different reactions that occur in the cell requires the participation of a specific enzyme. The study of the chemical properties of enzymes and the reactions they catalyze is a special, very important area of ​​biochemistry - enzymology.

Many enzymes are in the cell in a free state, being simply dissolved in the cytoplasm; others are associated with complex highly organized structures. There are also enzymes that are normally outside the cell; thus, enzymes that catalyze the breakdown of starch and proteins are secreted by the pancreas into the intestines. Secrete enzymes and many microorganisms.

The action of enzymes

Enzymes involved in the fundamental processes of energy conversion, such as the breakdown of sugars, the formation and hydrolysis of the high-energy compound adenosine triphosphate (ATP), are present in all types of cells - animal, plant, bacterial. However, there are enzymes that are produced only in the tissues of certain organisms.

Thus, the enzymes involved in the synthesis of cellulose are found in plant cells, but not in animal cells. Thus, it is important to distinguish between "universal" enzymes and enzymes specific to certain cell types. Generally speaking, the more specialized a cell is, the more likely it is to synthesize the set of enzymes needed to perform a particular cellular function.

A feature of enzymes is that they have high specificity, i.e., they can accelerate only one reaction or reactions of one type.

In 1890, E. G. Fisher suggested that this specificity is due to the special shape of the enzyme molecule, which exactly matches the shape of the substrate molecule. This hypothesis is called "key and lock", where the key is compared with the substrate, and the lock - with the enzyme. The hypothesis is that the substrate fits the enzyme like a key fits a lock. The selectivity of the enzyme action is related to the structure of its active center.

Enzyme activity

First of all, temperature affects the activity of the enzyme. As the temperature rises, the rate of a chemical reaction increases. The speed of molecules increases, they have more chances to collide with each other. Therefore, the likelihood that a reaction between them will occur increases. The temperature that provides the greatest activity of the enzyme is optimal.

Outside the optimum temperature, the reaction rate decreases due to protein denaturation. When the temperature decreases, the rate of a chemical reaction also decreases. At the moment when the temperature reaches the freezing point, the enzyme is inactivated, but it does not denature.

Enzyme classification

In 1961, a systematic classification of enzymes into 6 groups was proposed. But the names of enzymes turned out to be very long and difficult to pronounce, so it is now customary to name enzymes using working names. The working name consists of the name of the substrate on which the enzyme acts, followed by the ending "aza". For example, if the substance is lactose, that is, milk sugar, then lactase is the enzyme that converts it. If sucrose (ordinary sugar), then the enzyme that breaks it down is sucrase. Accordingly, enzymes that break down proteins are called proteinases.