TRANSMETHYLATION (synonym transmethylation) — the process of enzymatic transfer of methyl groups catalyzed by methyltransferases (KF 2. 1. 1) and leading to formation of new communication between the methyl group which is chipped off from the donor and the attacking reagent (acceptor). In quality coenzymes (see) methyltransferases S-adenozilmetionin, N-metiltetragidrofolat and methylcobalamine most often act. The item has big fiziol. value; it defines biosynthesis methionine (see), About - and N-methylation of proteins, acceptor RNA, DNA, G-methylation of steroids, About - and N-methylation of catecholamines also leads to formation of such biologically active agents as creatine (see), adrenaline (see), sincaline (see), anserine (see), N-metilnikotinamid (see. Niacin ), alkaloids (see), etc. Along with it methyl groups can participate in P. and be used for methylation of the toxic agents coming to an organism from the outside; e.g., methylcobalamine can serve as the donor of methyl groups at their enzymatic transfer in mikrobiol, objects to compounds of mercury, arsenic, selenium, tellurium, etc. with formation of highly toxic hetero-organic compounds, to-rye further can be transferred on to food chains (see) up to the higher organisms. E.g., the chloride formed as a result of such transfer to a methylmouth-ti almost completely passes into blood where can react with SH groups of hemoglobin, suppressing its ability to transfer oxygen. Disturbance of processes of P. (e.g., at a lack of intake of methionine with food) can lead to heavy funkts, frustration, including to fatty dystrophy of a liver. It is caused by the fact that the animal organism is almost not capable to synthesize methionine which comes to an organism with food in a free look or the need for it is satisfied at the expense of the remains of methionine which are formed as a result of hydrolysis of proteins in intestines. P.'s processes defining interaction of S-adenozilmetionina, connections of group folic acid (see) and methylcobalamine, play a paramount role in processes of a normal life cycle of cells. It is proved that intensive proliferation of the hemopoietic fabric at leukoses is followed by increase in concentration of methylcobalamine in blood of the person. It gives the grounds to assume an important role of disturbance of P. in development of data patol, processes.
A universal natural donor of methyl groups is S-adenozilmetionin. Except it N can be donors of methyl groups 5 - methyltetrahydrofolate, sincaline, betaine (see), methylamine, dimethylaunt's and metilkorrinoida. It is established that metilkorrinoida (coenzymes of vitamin B 12 ) take part in transfer of methyl groups on sulfur (in synthesis of methionine from a gomotsistein), on hydrogen (in biosynthesis of methane) and on carbonic acid (in biosynthesis of acetate).
Bibliography: Golenko O. D., etc. Influence of methylcobalamine on proliferative activity of cells of the hemopoietic fabric, Vopr. medical chemical, t. 20, No. 5, page 549, 1974; Flax and A. Biokhimiya's ndzher, the lane with English, page 633, M., 1974; F of i e d of of i with h W. Vitamin Bl2 und verwandte Corrinoide, Stuttgart, 1975; Wood J. M. Biological cycles for elements in the environment, Naturwissenschaften, S. 357, 1975.
I. P. Rudakova.