Flavin mononucleotide

Flavin mononucleotide (FMN) is a riboflavin-derived coenzyme whose isoalloxazine ring accepts and donates electrons in oxidation–reduction reactions. It often remains tightly bound to enzymes as a prosthetic group.

Isoalloxazine: A three-ring nitrogen-containing structure that forms the redox-active core of flavins. Its conjugated ring system accepts electrons and protons during FMN redox cycling.
Riboflavin: Vitamin B2, a water-soluble vitamin that serves as the precursor to FMN and FAD. FMN is made by phosphorylation of riboflavin.
Complex I: The mitochondrial respiratory-chain enzyme that oxidizes NADH and transfers electrons to ubiquinone. Its FMN accepts electrons from NADH at the start of the complex’s electron-transfer pathway.
Vitamin B2: An essential dietary vitamin, also called riboflavin, required for making FMN and FAD. FMN’s biosynthetic supply begins with this vitamin.
Electron transport chain: A series of membrane-associated electron carriers that transfer electrons and help generate a proton gradient. FMN-dependent respiratory enzymes feed electrons into this energy-conserving system.
Flavin redox chemistry: The reversible electron-transfer chemistry of flavins, including access to oxidized, semiquinone, and reduced states. FMN can mediate either one-electron or two-electron transfers through these states.
Flavin adenine dinucleotide: A flavin coenzyme consisting of FMN linked to an adenosine diphosphate group. FAD shares FMN’s redox-active core but carries an additional nucleotide group.
NADH dehydrogenase: An enzyme that oxidizes NADH and transfers its electrons to an acceptor. FMN is a common first electron acceptor in NADH dehydrogenases.
Flavokinase: An enzyme that uses ATP to phosphorylate riboflavin, producing FMN. It catalyzes the defining biosynthetic conversion from riboflavin to FMN.
Oxidative phosphorylation: The process that uses a proton gradient generated by respiration to drive ATP synthesis. FMN-supported electron flow can contribute to the gradient that powers ATP production.

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