Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as prosthetic group of various oxidoreductases including NADH dehydrogenase. During catalytic cycle, the reversible interconversion of oxidized (FMN), semiquinone (FMNH•) and reduced (FMNH2) forms occurs. FMN is a stronger oxidizing agent than NAD and is particularly useful because it can take part in both one and two electron transfers.
E106, a very closely related food dye, is riboflavin-5′-phosphate sodium salt, which consists mainly of the monosodium salt of the 5′-monophosphate ester of riboflavin. It is rapidly turned to free riboflavin after ingestion. It is found in many foods for babies and young children as well as jams, milk products and sweets and sugar products.