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Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B 2) 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. [1]
Riboflavin, also known as vitamin B 2, is a water-soluble vitamin and is one of the B vitamins. [3] [4] [5] Unlike folate and vitamin B 6, which occur in several chemically related forms known as vitamers, riboflavin is only one chemical compound.
Ribose 5-phosphate (R5P) is both a product and an intermediate of the pentose phosphate pathway. The last step of the oxidative reactions in the pentose phosphate pathway is the production of ribulose 5-phosphate. Depending on the body's state, ribulose 5-phosphate can reversibly isomerize to ribose 5-phosphate.
About 5-10% of flavoproteins have a covalently linked FAD. [2] Based on the available structural data, FAD-binding sites can be divided into more than 200 different types. [3] 90 flavoproteins are encoded in the human genome; about 84% require FAD and around 16% require FMN, whereas 5 proteins require both. [4]
In enzymology, a riboflavin phosphotransferase (EC 2.7.1.42) is an enzyme that catalyzes the chemical reaction. alpha-D-glucose 1-phosphate + riboflavin D-glucose + FMN. Thus, the two substrates of this enzyme are alpha-D-glucose 1-phosphate and riboflavin, whereas its two products are D-glucose and FMN.
It is formed by phosphogluconate dehydrogenase in the pentose phosphate pathway. [1] [2] Ribulose 5-phosphate is involved in various metabolic pathways. Ribulose 5-phosphate can be acted upon by phosphopentose isomerase to form ribose 5-phosphate, which is a precursor for nucleotide and co-factor biosynthesis. [1]
The enzyme FAD-AMP lyase (cyclizing) (EC 4.6.1.15) catalyzes the reaction . FAD AMP + riboflavin cyclic-4′,5′--phosphate. This enzyme belongs to the family of lyases, specifically the class of phosphorus-oxygen lyases.
The riboflavin synthase monomer has a molecular weight of about 23 kDa. Each monomer contains two beta barrels and one α-helix at the C-terminus (residues 186-206). The monomer folds into pseudo two-fold symmetry, predicted by sequence similarity between the N-terminus barrel (residues 4-86) and the C-terminus barrel (residues 101-184). [1]