Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Vitamins
Vitamin-like substances
Antivitamins

Currently, antivitamins are generally divided into two groups: 1) antivitamins with a Structure similar to that of the native vitamin, whose action is based on competitive relationships with it; and 2) antivitamins that cause Modification of the Chemical Structure of Vitamins or impede their absorption and transport, resulting in a reduction or loss of the biological effect of the vitamins. Thus, the term “antivitamins” refers to any substances that, regardless of their MECHANISM OF ACTION, cause a decrease or complete loss of the biological activity of vitamins.

Structure-like antivitamins (some of which have been mentioned previously) are essentially antimetabolites and, upon interaction with the apoenzyme, form an inactive enzyme complex, shutting down the enzymatic reaction with all ensuing consequences.

In addition to structure-like vitamin analogs, the administration of which leads to The Development of true avitaminoses, there are antivitamins of biological origin, including Enzymes and Proteins that cause the Cleavage or binding of vitamin molecules, depriving them of their physiological action. These include, for example, thiaminases I and II, which cause The breakdown of the vitamin B₁ molecule; ascorbate oxidase, which catalyzes the destruction of Vitamin C; and the protein Avidin, which binds biotin into a biologically inactive complex. Most of these antivitamins are used as therapeutic agents with a strictly targeted effect on certain biochemical and physiological processes. In particular, among the antivitamins of Fat-soluble vitamins, dicumarol, warfarin, and tromexan (vitamin K antagonists) are used as anticoagulant drugs. Well-studied thiamine antivitamins include oxythiamine, pyri- and neopyrithiamine; riboflavin antivitamins include atebrin, quinacrine, galactoflavin, and isoriboflavin (all of which compete with vitamin B₂ in The Biosynthesis of the Coenzymes FAD and FMN); and pyridoxine antivitamins include deoxypyridoxine, cycloserine, and isonicotinic acid hydrazide (isoniazid), which exerts an antibacterial effect on Mycobacterium tuberculosis. Antivitamins of Folic acid include amopterin and methotrexate; vitamin B₁₂ antivitamins include derivatives of 2-aminomethylpropanol-B₁₂; nicotinic acid antivitamins include isoniazid and 3-acetylpyridine; and p-aminobenzoic acid antivitamins include sulfonamide drugs. All of these have found widespread application as antitumor or antibacterial agents by inhibiting PROTEIN AND NUCLEIC acid synthesis in Cells.