Flavin mononucleotide (FMN), or
riboflavin-5'-phosphate, is a
biomolecule produced from
riboflavin (vitamin B
2) by the enzyme
riboflavin kinase and functions as
prosthetic group of various
oxidoreductases including
NADH dehydrogenase as well as cofactor in biological blue-light photo receptors. During the catalytic cycle, a reversible interconversion of the oxidized (FMN), semiquinone (FMNH
•) and reduced (FMNH
2) forms occurs in the various oxidoreductases. FMN is a stronger oxidizing agent than
NAD and is particularly useful because it can take part in both one- and two-electron transfers. In its role as blue-light photo receptor, (oxidized) FMN stands out from the 'conventional' photo receptors as the signaling state and not an E/Z isomerization.