:"For the town in France, see
Flavin, Aveyron".Flavin (from Latin "flavus", "yellow") is the common name for a group of organic compoundsbased on pteridine, formed by the tricyclic heteronuclear organic ring isoalloxazine. The biochemical source is the vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphateto form flavin adenine dinucleotide(FAD), and, in other circumstances, is found as flavin mononucleotide(or FMN), a phosphorylatedform of riboflavin. It is in one or the other of these forms that flavin is present as a prosthetic groupin flavoproteins.
The flavin group is capable of undergoing
oxidation-reduction reactions, and can accept either one electronin a two-step process or two electrons at once. Reduction is made with the addition of hydrogenatoms to specific nitrogenatoms on the isoalloxazine ring system:
aqueous solution, flavins are yellow-coloured when oxidized, taking a red colour in the semi-reduced anionic state or blue in the neutral ( semiquinone) state, and colourless when totally reduced.cite journal |last= Michaelis|first= Leonor|authorlink= |coauthors=M. P. Schubert, C. V. Smythe |year= 1936|month= Dec|title= Potentiometric Study of the Flavins|journal= J. Biol. Chem.|volume= 116|number= 2|pages= 587–607|id= |url= http://www.jbc.org/cgi/reprint/116/2/587|accessdate= 2008-04-25] The oxidized and reduced forms are in fast equilibrium with the semiquinone ( radical) form, shifted against the formation of the radical:cite journal |last= Massey|first= Vincent|authorlink= |coauthors=M. Stankovich, Peter Hemmerich |year= 1978|month= Jan|title= Light-Mediated Reduction of Flavoproteins with Flavins as Catalysts|journal= Biochemistry|volume= 17|number= 1|pages= 1–8|id= |url= http://pubs.acs.org/cgi-bin/archive.cgi/bichaw/1978/17/i01/pdf/bi00594a001.pdf|accessdate= 2008-04-25|doi= 10.1021/bi00594a001]
::Flox + FlredH2 ⇌ FlH•
where Flox is the oxidized flavin, FlredH2 the reduced flavin (upon addition of two hydrogen atoms) and FlH• the semiquinone form (addition of one hydrogen atom).
In the form of FADH2, it is one of the cofactors that can transfer electrons to the
electron transfer chain.
Both free and protein-bound flavins are photoreducible, that is, able to be reduced by
light, in a mechanism mediated by several organic compounds, such as some aminoacids, carboxylic acids and amines.
Flavin adenine dinucleotide is a group bound to many enzymes including
ferredoxin-NADP+ reductase, monoamine oxidase, D-amino acid oxidase, glucose oxidase, xanthine oxidase, and acyl CoA dehydrogenase.
FADH and FADH2 are reduced forms of FAD. FADH2 is produced as a prosthetic group in
succinate dehydrogenase, an enzyme involved in the citric acid cycle. In oxidative phosphorylation, two molecules of FADH2 typically yield 1.5 ATP each, or three ATP combined.
Flavin mononucleotideis a prosthetic groupfound in, among other proteins, NADH dehydrogenase, "E.coli" nitroreductase and old yellow enzyme.
Use as a dye
Flavin is the most important coloring matter obtained from
quercitron(the bark of "Quercus velutina", also called dyer's oak). "Flavin" is the commercial name for quercitron. Two preparations are "yellow flavin" and "red flavin," which contains only quercetin. [http://en.wikipedia.org/wiki/New_International_Encyclopedia]
* Voet, D.; Voet, J.G. (2004). "Biochemistry" (3rd ed.). John Wiley & Sons. ISBN 0-471-39223-5
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