Biology:Flavin

Flavin is a tricyclic heteronuclear organic ring based on pteridine whose biochemical source is the vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD), and in other circumstances, is found as flavin mononucleotide (or FMN), a phosphorylated form of riboflavin. The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two step process or can accept two electrons at once. In the form of FADH₂, it is one of the cofactors that can transfer electrons to the electron transfer chain. Since FMN fluoresces more than FAD, these flavins can be readily distinguished experimentally through a simple fluorescence-based assay. In this assay, the 530 nm fluorescence (upon a 360 nm excitation) of a sample solution is measured before and after treatment with Naja naja venom. Under these conditions the fluorescence of FMN solutions does not change, but the phosphodiesterases present in the venom cleave FAD into FMN and adenine, yielding a 10-fold increase of fluorescence of FAD solutions [1].

FAD

Flavin adenine dinucleotide is a cofactor in the enzymes monoamine oxidase, D-amino acid oxidase, glucose oxidase, and xanthine oxidase.

FADH / FADH₂

FADH and FADH₂ are (respectively) one-electron and two-electron reduced forms of FAD. FADH₂ is produced in the citric acid cycle. In oxidative phosphorylation, one molecule of FADH₂ yields approximately 1.5 ATP

FMN

Flavin mononucleotide is a prosthetic group found in NADH dehydrogenase. image:flavin.png

See also

• Pteridine
• Pterin

References

• Voet, D.; Voet, J.G. (2004). Biochemistry (3rd ed.). John Wiley & Sons. ISBN 0-471-39223-5