<unk>  is a tricyclic heteronuclear organic ring based on pteridine whose biochemical source is the vitamin riboflavin. The<unk>  moiety is often attached with an adenosine diphosphate to form<unk>  adenine dinucleotide (FAD), and in other circumstances, is found as<unk>  mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that<unk>  is present as a prosthetic group in flavoproteins.
The<unk>  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.
Flavin
Coenzyme
Chlorophyll
Hydroquinone
Biotin
Glycobiarsol
Hemin
Heme