flavinemononucleotide

Flavin mononucleotide (FMN) is a riboflavin-derived coenzyme that functions as a prosthetic group for a broad family of flavoproteins. It consists of the flavin mononucleotide moiety attached to a ribose phosphate chain. In cells FMN exists in oxidized form, as well as in reduced forms FMNH2 and the one-electron reduced semiquinone FMNH•, allowing it to participate in both one- and two-electron transfer reactions.

Biosynthesis and interconversion with other flavin cofactors are central to FMN biology. FMN is produced from dietary riboflavin by riboflavin kinase, which phosphorylates riboflavin to give FMN. FMN can be further converted to flavin adenine dinucleotide (FAD) by FMN adenylyltransferase. Together, these two cofactors (FMN and FAD) comprise the main flavin pool used by cells to support redox metabolism.

Function and distribution in metabolism are broad. FMN serves as a cofactor for numerous flavoproteins, including oxidoreductases and dehydrogenases, where it mediates electron transfer to or from other carriers such as iron-sulfur clusters or ubiquinone. In mitochondria and many bacteria, FMN plays a key role in the initial steps of the electron transport chain, accepting electrons from NADH in complex I and funneling them into the respiratory chain. FMN-containing enzymes participate in a variety of metabolic pathways, reflecting the versatile redox chemistry of the flavin moiety.

Physiological relevance and nutrition are linked to riboflavin status, since FMN is derived from this vitamin. Inadequate riboflavin intake can impair FMN- and FAD-dependent enzymes, contributing to clinical signs of riboflavin deficiency. FMN is also used in biochemical research due to its spectral properties and redox activity.