Flavin mononucleotide (FMN) is a cofactor that helps catalyze a wide range of reactions. It is also known as riboflavin 5'-phosphate. The structure of FMN consists of three main parts, the isoalloxazine ring, the ribitol group, and a phosphate. FMN can exist in any of three different redox states. It can participate in one-electron transfer and two-electron transfer reactions. Because it is able to do this, it is able to catalyze a wide array of reactions, and also work with many other electron donors and acceptors.
There is a wide range of different enzyme catalyzed reactions that are catalyzed using FMN as a cofactor. Some of these include trimethylamine dehydrogenase, NADPH-cytochrome P450 reductase, glycolate oxidase, dihydroorotate dehydrogenase A, and NADPH-flavin oxidoreductase.
One of the reactions catalyzed by using the cofactor FMN involves the enzyme glycolate oxidase. Glycolate oxidase is a peroxisomal enzyme. It catalyzes the oxidation of alpha-hydroxy acids. It is one of the key enzymes in photorespiration, where it oxidizes glycolate to glyoxylate. Another enzyme that uses FMN as a cofactor is dihydroorotate dehydrogenase (DHOD). It catalyzes the conversion of (S)-dihydroorotate to orotate. This is the fourth step in the de novo biosynthesis of pyrimidine nucleotides. A third enzyme that uses FMN as a cofactor is flavin reductase P. NAD(P)H: flavin oxidoreductases (flavin reductases) catalyze the reduction of flavin by using NAD(P)H. They are involved in the role of bacterial bioluminescence. They have been detected in luminous bacteria where they are believed to provide FMNH2 (reduced FMN) to luciferase in vivo where it acts as a substrate for the luminescence reaction.