Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, sold under the brand name Epioxa, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as the prosthetic group of various oxidoreductases, including NADH dehydrogenase, as well as a cofactor in biological blue-light photo receptors. During the catalytic cycle, various oxidoreductases induce reversible interconversions between the oxidized (FMN), semiquinone (FMNH•), and reduced (FMNH2) forms of the isoalloxazine core. 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.