Enzymes are globular proteins that help all cellular processes to proceed. 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 strictly defined organelles. The localization of enzymes is directly related to the function that this part of the cell usually performs.
Almost all glycolysis enzymes are located in the cytoplasm. Enzymes of the tricarboxylic acid cycle are in the mitochondrial matrix. The active substances of hydrolysis are contained in lysosomes.
Individual 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 visible 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 - "thin", Greek)
- Rational. The name of the enzyme consists of the substrate and the ending "-ase". For example, amylase accelerates the hydrolysis of starch (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. Name reflects:
- substrate - alanine;
- acceptor - 2-oxoglutaric acid;
- an 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.
Classification of enzymes
There are two ways to divide enzymes into groups. 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.
Into the non-protein partcomplex enzyme may include vitamins. Interaction with other substances occurs through the active center. The whole enzyme molecule does not take part in the process.
Properties of enzymes, like other proteins, are determined by their structure. Depending on it, catalysts accelerate only their reactions.
The second method of classification divides substances according to the function of enzymes. The result is six classes:
- oxidoreductase;
- transferases;
- hydrolases;
- isomerase;
- lyases;
- ligases.
These are generally accepted groups, they differ not only in the types of reactions that regulate the enzymes in them. 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.
- 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.
- Primarydehydrogenases 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.
Eight groups of catalysts are distinguished based on the transferred group. Let's look at just a few of them.
- Phosphotransferases - help transfer phosphoric acid residues. They are divided into subclasses according to the destination (alcohol, carboxyl and others).
- Aminotransferases – accelerate amino acid transamination reactions.
- Glycosyltransferases - transfer glycosyl residues from phosphorus ester molecules to mono- and polysaccharide molecules. Provide reactionsbreakdown and synthesis of oligo- or polysaccharides in plants and animals. For example, they are involved in the breakdown of sucrose.
- 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. Acetic acid acyl is most commonly tolerated.
Hydrolases - split with 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 location 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 the 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.
Separate several types of catalysts from this group:
- esterases - responsible for the hydrolysis of alcohol esters;
- glycosidases - accelerate the hydrolysis of glycosides, depending onwhat isomer do they act, 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 the 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;
- moving the phosphate group;
- changing the arrangement of atomic groups in space;
- moving 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 breakdown of organic compounds by bonds:
- carbon-carbon;
- phosphorus-oxygen;
- carbon-sulphur;
- carbon-nitrogen;
- carbon-oxygen.
In this case, such simple products as carbon dioxide, water, ammonia are released, and double bonds are closed. Few of these reactions can go in the opposite direction, the corresponding enzymes in the appropriateunder this conditions catalyze the processes of not only decay, but also synthesis.
Liases are classified according to the type of bond they break. They are complex enzymes.
Ligase crosslinks
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 especially 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 DNA molecules 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. All that remains is to clean it up and it will help many sick people.
The huge role of enzymes in the body
They canincrease the reaction rate by 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, and are part of washing powders. They are also used in the manufacture of photographic materials.
