Catalase is an enzyme found in almost all living organisms. Its main function is to catalyze the decomposition reaction of hydrogen peroxide to substances harmless to the body. Catalase is of great importance for the life of cells, as it protects them from destruction by reactive oxygen species.
General information
The enzyme catalase belongs to oxidoreductases, a broad class of enzymes that catalyze the transfer of electrons from a reducing (donor) molecule to an oxidizing (acceptor) molecule.
The optimal pH for catalase to work in the human body is about 7, however, the reaction rate does not change significantly at 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 optimal temperature also varies, for a person it is about 37o C.
Catalase is one of the fastest enzymes. Just one molecule of it is capable of converting millions of hydrogen peroxide molecules into water and oxygen in a matter of minutes.give me a sec. From an enzymological point of view, this means that the enzyme catalase is characterized by a large number of turnovers.
Enzyme structure
Catalase is a tetramer of four polypeptide chains, each of which is more than 500 amino acids long. The enzyme has four groups of porphyritic heme, thanks to which it reacts with reactive oxygen species. Oxidized heme is the prosthetic group of catalase.
Discovery history
Catalase was not known to scientists until 1818, when Louis Jacques Tenard, the 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 Löw first coined the term "catalase" to refer to the mysterious peroxide-decomposing substance. He also managed to answer the question of where the enzyme catalase is contained. As a result of numerous experiments, Oscar Lev 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 was first crystallized from beef liver. In 1938, the molecular weight of the enzyme was determined - 250 kDa. In 1981, scientists imaged the three-dimensional structure of bovine catalase.
Catalysis of hydrogen peroxide
Despite the fact that hydrogen peroxide isa 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 enzyme catalase does exactly this task - it decomposes a peroxide molecule into two water molecules and an oxygen molecule.
The decomposition reaction of hydrogen peroxide in living tissues:
2 H2O2 → 2 H2O + O 2
The molecular mechanism of the breakdown of hydrogen peroxide by the enzyme catalase has not yet been accurately studied. It is assumed that the reaction takes place in two stages - at the first stage, iron in the prosthetic group of catalase binds to the oxygen atom of the peroxide, and one molecule of water is released. In the second step, the oxidized heme reacts with another hydrogen peroxide molecule, resulting in the formation of another water molecule and one oxygen molecule.
Due to this action of the enzyme catalase on hydrogen peroxide, the presence of this active substance in tissue samples is easy to determine. To do this, it is enough to add a small amount of hydrogen peroxide to the test sample and observe the reaction. The presence of the enzyme is indicated by the formation of oxygen bubbles. This reaction is good because it does not require any special equipment or instruments - it can be observed with the naked eye.
It is worth noting that the ionany 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 catalase enzyme on hydrogen peroxide has found application in the food industry - with the help of this enzyme, milk is removed H2O 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 fabrics.
It is used in small amounts in contact lens hygiene. Some disinfectants contain hydrogen peroxide and catalase is used to break down this compound before reusing the lenses.
Activity
The activity of the enzyme catalase depends on the age of the body. In young tissues, the activity of the enzyme is much higher than in old ones. With age, both in 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 hair. Hydrogen peroxide is constantly formed in the human body, but does not 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, dissolvingnatural dyes. This unexpected discovery is now being tested by researchers and may play a role in the development of drugs that stop graying of hair.
