Flavoproteins

Flavoproteins are a class of proteins that contain a flavin nucleotide, most commonly flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN), as a prosthetic group or tightly bound cofactor. The flavin moiety is derived from riboflavin (vitamin B2) and enables a broad repertoire of redox chemistry essential to cellular metabolism.

Cofactor properties: FAD and FMN participate in one- and two-electron transfers and can cycle through multiple oxidation states, including the fully reduced and semiquinone forms. In many flavoproteins the flavin is noncovalently bound within a protein pocket; in a subset it is covalently linked to amino acid residues, which can adjust redox potential and spectral properties.

Functions and examples: Flavoproteins catalyze oxidation–reduction reactions in energy production, biosynthesis, and detoxification. They include succinate dehydrogenase (a component of complex II in respiration), various acyl-CoA dehydrogenases in fatty acid beta-oxidation, monooxygenases and oxidases (for example, glucose oxidase and D-amino acid oxidase), and glutathione reductase. Some flavoproteins also function in light sensing or bioluminescence, such as luciferase and photolyases that repair UV-induced DNA damage.

Diversity and structure: Flavoproteins exhibit diverse structural folds. The flavin may participate directly in substrate oxidation by transferring electrons to the flavin, which then passes them to downstream carriers such as NAD+, ubiquinone, or molecular oxygen. The same cofactor can support different types of chemistry across enzyme families.

Physiology and nutrition: Riboflavin deficiency impairs flavoprotein function and can disrupt energy metabolism and antioxidant defenses; proper intake of vitamin B2 is essential for maintaining flavoprotein-dependent processes.