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(also flavin enzyme or yellow enzyme), any one of a group of complex enzymes, whose riboflavin derivatives—flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN)—serve as prosthetic groups (non-protein components). Flavoproteins were discovered in 1932 by O. Warburg.
The prosthetic group of many flavoproteins contains, in addition to flavin nucleotides, metals (Fe, Cu, Mo), sulfur compounds, and other compounds. The metals are complexly bound to the flavin nucleotides. When in an oxidized state, most flavoproteins are colored yellow and have characteristic absorption bands in the ranges 350–380 and 450–460 nanometers; in a reduced state, they are colorless. Flavoproteins are related to the oxidoreductase class and catalyze important oxidation-reduction reactions in living organisms with the direct participation of FAD and, more rarely, FMN. The specificity (selectivity) and effectiveness of the action of flavoproteins are determined by the nature of their protein components (apoenzymes), which have still not been adequately studied. Most flavoproteins are associated with cell membranes, forming strong complexes with lipids that are part of their composition.
The primary function of flavoproteins is the oxidation of reduced nicotinamide adenine dinucleotide in electron transfer chains (seeOXIDATIVE PHOSPHORYLATION). Flavoproteins are also capable of directly oxidizing various substrates and detaching from them hydrogen atoms, which are then transferred onto oxygen either immediately (for example, xanthine oxidase) or through the chain of transfer of electrons (for example, succinate dehydrogenase).
Flavoproteins are abundant in nature; they participate in the catabolism of major classes of organic compounds in the cells of animals, plants, and microorganisms.
REFERENCELehninger, A. Biokhimiia. Moscow, 1976. (Translated from English.)
N. N. CHERNOV