Catalase is an enzyme found in almost all living organisms. Its main function is to catalyze the decomposition of hydrogen peroxide to substances that are harmless to the body. Catalase is of great importance for the vital activity of cells, as it protects them from destruction by reactive oxygen species.
General information
The catalase enzyme belongs to oxidoreductases - an extensive class of enzymes that catalyze electron transfer from a reducing molecule (donor) to an oxidizing molecule (acceptor).
The optimal pH for catalase in the human body is about 7, however, the reaction rate does not change significantly with hydrogen values from 6.8 to 7.5. The optimal pH for other catalases ranges from 4 to 11, depending on the type of organism. The optimum temperature also varies, for a person it is about 37 ° C.
Catalase is one of the fastest enzymes. Only one of its molecules is capable of converting millions of hydrogen peroxide molecules into water and oxygen in a second. From the point of view of enzymology, this means that the catalase enzyme is characterized by a large number of revolutions.
Enzyme structure
Catalase is a tetramer of four polypeptide chains, each of which has a length of more than 500 amino acids. The enzyme contains four groups of porphyry heme, due to which it reacts with reactive oxygen species. Oxidized heme is a prosthetic catalase group.
Discovery story
Catalase was not known to scientists until 1818, until Louis Jacques Tenard, a chemist who discovered hydrogen peroxide in living cells, suggested that its destruction was due to the action of a previously unknown biological substance.
In 1900, the German chemist Oscar Lev was the first to introduce the term “catalase” to mean a mysterious substance that decomposes peroxides. He managed to answer the question of where the catalase enzyme is contained. As a result of numerous experiments, Oscar Leo revealed that this enzyme is characteristic of almost all animal and plant organisms. In a living cell, like many other enzymes, catalase is found in peroxisomes.
In 1937, catalase from beef liver was first crystallized. In 1938, the molecular weight of the enzyme was determined - 250 kDa. In 1981, scientists obtained an image of the three-dimensional structure of bovine catalase.
Catalysis of hydrogen peroxide
Despite the fact that hydrogen peroxide is a product of many normal metabolic processes, it is not harmless to the body.
To prevent the destruction of cells and tissues, hydrogen peroxide must be quickly converted into another, less dangerous substance for the body. The catalase enzyme copes with this very task - it decomposes a peroxide molecule into two water molecules and an oxygen molecule.
The decomposition of hydrogen peroxide in living tissues:
2 H 2 O 2 → 2 H 2 O + O 2
The molecular mechanism of the breakdown of hydrogen peroxide by the enzyme catalase has not yet been precisely studied. It is assumed that the reaction proceeds in two stages - at the first stage, iron as a part of the prosthetic catalase group binds to the oxygen atom of peroxide, and one water molecule is released. At the second stage, the oxidized heme interacts with another molecule of hydrogen peroxide, as a result of which another water molecule and one oxygen molecule are formed.
Due to this action of the enzyme catalase on hydrogen peroxide, the presence of this active substance in tissue samples is easy to determine. For this, it is enough to add a small amount of hydrogen peroxide to the test sample and observe the reaction. The presence of an enzyme is indicated by the formation of oxygen bubbles. This reaction is good because it does not require any special equipment or tools - it can be observed with the naked eye.
It is worth noting that the ion of any heavy metal can act as a non-competitive catalase inhibitor. In addition, the well-known cyanide behaves as a competitive inhibitor of catalase if there is a lot of hydrogen peroxide in the tissues. Arsenates play the role of activators.
Application
The decomposing effect of the enzyme catalase on hydrogen peroxide has found application in the food industry - with the help of this enzyme it is removed from milk H 2 O 2 before making cheese. Another application is special food packaging that protects products from oxidation. Catalase is also used in the textile industry to remove hydrogen peroxide from tissues.
It is used in small amounts in contact lens hygiene. Some disinfectants contain hydrogen peroxide, and catalase is used to break down this component before reusing lenses.
Activity
The activity of the catalase enzyme depends on the age of the body. In young tissues, enzyme activity is significantly higher than in old ones. With age, in both humans and animals, catalase activity gradually decreases as a result of aging of organs and tissues.
According to a recent study, a decrease in catalase activity is one of the possible causes of graying. Hydrogen peroxide is constantly formed in the human body, but does no harm - catalase quickly decomposes it. But if the level of this enzyme is reduced, it is obvious that not all hydrogen peroxide is catalyzed by the enzyme. Thus, it bleaches the hair from the inside, dissolving natural dyes. This unexpected discovery is now being tested by researchers, and may play a role in the development of drugs that stop graying hair.