From Big Medical Encyclopedia

ANTIMETABOLITES (Greek anti-against + a metabolite[s]) — substances which owing to the structural proximity or bigger activity in relation to natural metabolic products (metabolites) can replace them in biochemical reactions. However, having certain differences in a structure of a molecule, And. cannot provide the further normal course of these reactions, than and cause change of processes of a metabolism.

The major group A. make structural analogs vitamins (see), hormones (see) and mediators (see).

Since the majority of vitamins is components of enzymes, introduction of an antimetabolite of vitamin (antivitamin) to an organism leads to formation of an inactive analog of the enzyme incapable to carry out functions of the specific catalyst inherent in normal enzyme. Thereof there are phenomena characteristic of deficit of the corresponding vitamin.

At introduction to an organism ftornikotinovy to - you, serving as an antimetabolite of RR vitamin (niacinamide), instead of diphosphopyridindinucleotide (nicotinamide adenine dinucleotide, the kodegidrogenaz) who is a coenzyme of dehydrogenases are formed similar dinucleotide, in Krom the place of amide nicotinic to - you take amide ftornikotinovy to - you. Such nucleotide competes for an apoenzyme with a natural nucleotide, taking its place, however it cannot perform functions of a coenzyme in reactions of dehydrogenation. Such is the principle of action of the majority of antivitamins.

Streptocides — analogs paraaminobenzoic to - you; the last serves as a component of coenzymes of group folic to - you. The medical effect of streptocides is caused by the fact that they are included coenzymes of microorganisms and by that cause in them disturbance of the vital substances of exchange reaction.

One of And. hormones the structural analog of an adrenal hormone of a cortisone — 2-метил9(α)-фторкортизол is. This connection prevents development of an atrophy of a thymus and follicles of a spleen, and also some other pathological phenomena caused by a cortisone.

As powerful antagonists of the serotonin (see) possessing a broad spectrum of activity on an organism serve medmain, derivatives lysergic to - you, etc. As some of these And. cause the disturbances of mentality characteristic of schizophrenia (a hallucination, the crazy ideas, the wrong behavior, etc.), believe that disturbances of exchange of serotonin play an essential role in a pathogeny of this disease.

Special group A. make analogs of the purine and pirimidinovy bases which are a part nucleinic to - t, and analogs of amino acids of which proteins are under construction. Thiouracil — a structural analog of the uracil entering a molecule ribonucleic to - you a virus of a tobacco mosaic — in the sheet of tobacco joins in molecules of nucleic acids of again formed virus particles then these atypical viruses lose ability to further self-reproduction. With similar image 6 azauracil affect microbic cells, interfering with inclusion of a natural metabolite of uracil in their nucleinic to - you. 6 Azauracil have also carcinostatic properties.

And. can be applied as chemotherapeutic drugs. In some cases, when the course of processes of a metabolism has pathological character, introduction And. can contribute to normalization of functions of an organism. However use And. as medicinal substances it is strongly limited to the fact that many of them are antagonists of metabolites both a microbic cell, and cells of a human body. In such cases use And. it is possible if a microorganism of a pla the struck fabric has ability selectively to absorb and accumulate And. E.g., it is possible to use analogs of the purine and pirimidinovy bases as carcinostatic substances since fabric of a tumor differs in an intensive metabolism, in particular in intensive synthesis of nucleic acids owing to what entered And. preferential comes to tumoral fabric. And. widely apply also as insecticides, fungicides, disinfecting substances; napr, hexachlorane represents an analog of the inositol which is vitamin for many organisms.

See also Antigormona , Metabolism and energy .

Bibliography: Albert E. Selective toxicity, the lane with English, M., 1971; In at l of l and. The doctrine about antimetabolites, the lane with English, M., 1954, bibliogr.; Maister A. Biochemistry of amino acids, the lane with English, page 139, M., 1961; T r at f An about in A. V. Biokhimiya and physiology of vitamins and antivitamins, M., 1959; Uebbl. Inhibitors of enzymes and metabolism, the lane with English, M., 1966, bibliogr.

A. Ya. Nikolaev.