Flavoproteine

Flavoproteins are proteins that contain a flavin nucleotide cofactor, most commonly flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). These cofactors are derived from riboflavin (vitamin B2) and can be bound tightly as prosthetic groups or more loosely as cofactors. In many flavoproteins the flavin is covalently attached to the polypeptide, though non-covalent binding is also common. The flavin’s ability to undergo reversible redox reactions enables one- and two-electron transfers, allowing flavoproteins to participate in a wide range of oxidative and reductive processes.

Flavoproteins play essential roles in metabolism and energy production. In the mitochondrial and bacterial electron transport chains, flavins serve as initial electron carriers in Complex I (FMN-containing) and in Complex II (FAD-containing) of the respiratory chain. Other flavoproteins function as dehydrogenases, oxidases, reductases, and monooxygenases. Distinct families include flavin-containing monooxygenases (FMOs) that introduce oxygen atoms into substrates, and various flavoprotein dehydrogenases involved in fatty acid beta-oxidation and amino acid metabolism. Some flavoproteins are also involved in bioluminescence, such as luciferase enzymes that use FMN/FAD to emit light.

Flavoproteins are widespread in bacteria, archaea, plants, and animals; many are essential for metabolism, redox homeostasis, and detoxification. Defects in flavoproteins can lead to metabolic disorders and increased susceptibility to oxidative stress. In research and industry, flavoproteins are used in biocatalysis and biosensors due to their redox properties.