Enzymes are globular proteins that help all cellular processes. Like all catalysts, they cannot reverse the reaction, but serve to accelerate it.
Enzyme localization in the cell
Inside the cell, individual enzymes, as a rule, are contained and act in strictly defined organelles. The localization of enzymes is directly related to the function that this section of the cell usually performs.
Almost all glycolysis enzymes are located in the cytoplasm. The 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 tissue feature is used in the clinic for the diagnosis of certain diseases.
There are also age-related features in the activity and set of enzymes in the 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 varying degrees.
- Trivial. The names of the substances are given by random signs. For example, pepsin (pepsis - "digestion", Greek) and trypsin (tripsis - "thin", Greek.)
- Rational. The name of the enzyme is composed of the substrate and the end of "-az". For example, amylase accelerates the hydrolysis of starch (amylo - "starch", Greek.).
- Moscow. It was adopted in 1961 by the international commission on the nomenclature of enzymes at the V International Biochemical Congress. The name of the substance is made up of the substrate and the reaction, which 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, the enzyme alanine: 2-oxoglutarate aminotransferase is involved in the reaction of transferring an amino group from alanine to 2-hydroxyglutaric acid. The name reflects:
- substrate - alanine;
- the acceptor is 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.
Enzyme classification
There are two ways to divide enzymes into groups. The first offers two classes of these substances:
- simple - consist only of protein;
- complex - contain the protein part (apoenzyme) and non-protein, called coenzyme.
The non-protein part of a complex enzyme may include vitamins. 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 what function the enzymes perform. The result is six classes:
- oxidoreductases;
- 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. The substances of various groups have a different structure. And the functions of enzymes in the 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 the transfer of electrons or hydrogen atoms from the very first substrate to the final acceptor is carried out. These substances are separated by the principle of work or by 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 occur without the transfer of electrons or hydrogen atoms to oxygen atoms.
- Primary dehydrogenases catalyze the process of weaning hydrogen atoms from an oxidizable 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 oxidation-reduction reactions. This is achieved by a large number of options: one and the same coenzyme can join different apoenzymes. In each case, a special oxidoreductase with its own properties is obtained.
There is another function of the enzymes of this group, which cannot be ignored - they accelerate the flow 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 isolated based on the transferred group. We will consider only some of them.
- Phosphotransferases - help transfer residues of phosphoric acid. They are divided into subclasses in accordance with the destination (alcohol, carboxyl and others).
- Aminotransferases - accelerate the transamination of amino acids.
- Glycosyl transferases - transfer glycosyl residues from phosphorus ester molecules to mono- and polysaccharide molecules. Provide the reaction of decomposition and synthesis of oligo - or polysaccharides in plants and animals. For example, they are involved in the decomposition 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. The most commonly tolerated acyl acetic acid.
Hydrolases - cleaved with water
In this group, enzymes act as catalysts for the cleavage (less often synthesis) reactions of organic compounds in which water is involved. Substances of this group are found in cells and in digestive juice. The molecules of the catalysts in the digestive tract consist of one component.
The 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 appears, 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 alcohol esters;
- glycosidases - accelerate the hydrolysis of glycosides, depending on which isomer 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 decomposition of urea into ammonia and water.
Isomerase - Molecule Transformation
These substances accelerate changes within a single molecule. They can be geometric or structural. This can happen in many ways:
- hydrogen atom transfer;
- phosphate group movement;
- changing the location of atomic groups in space;
- moving double bond.
Organic acids, carbohydrates or amino acids may be isomerized. Isomerases can convert aldehydes to ketones and, conversely, rearrange the cis form to trans form and vice versa. In order to better understand what function the enzymes of this group perform, it is necessary to know the differences in the isomers.
Liases tear bonds
These enzymes accelerate the non-hydrolytic decomposition of organic compounds in bonds:
- carbon-carbon;
- phosphorus oxygen;
- carbon sulfur;
- carbon nitrogen;
- carbon oxygen.
In this case, such simple products as carbon dioxide, water, ammonia stand out and double bonds are closed. Few of these reactions can go in the opposite direction, the corresponding enzymes in suitable conditions for this catalyze the processes of not only decomposition, but also synthesis.
Classification of lyases occurs according to the type of bond that they break. They are complex enzymes.
Ligases are crosslinked
The main function of the enzymes in this group is to accelerate the synthesis reactions. Their feature is the conjugation of 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 subgroups of lyases, 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 cross-links 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 crosslink DNA molecules from the pieces they need, creating unique chains of deoxyribonucleic acid. They can lay any information, thus creating a factory for the production of necessary proteins. For example, you can embed in a bacterial DNA a piece responsible for the synthesis of insulin. And when the cell will translate its own proteins, it at the same time will make a useful substance that is necessary for medical purposes. It remains only to clean it, and it will help many sick people.
The huge role of enzymes in the body
They can increase 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, as are all the ongoing processes. And the disruption of these catalysts leads to dire consequences.
Enzymes are widely used in food, light industry, and medicine: they are used for the manufacture of cheeses, sausages, canned food, and are part of washing powders. They are also used in the manufacture of photographic materials.