Koenzyme

A coenzyme is a non-protein organic molecule that binds to an enzyme and is essential for catalytic activity. Coenzymes often act as carriers for electrons, atoms, or functional groups during enzymatic reactions. Most coenzymes are derived from vitamins, and their availability affects enzyme activity; they are distinct from inorganic cofactors such as metal ions.

Coenzymes can be categorized as prosthetic groups, which are tightly bound to the enzyme, or as cosubstrates, which bind reversibly and are released after the reaction and must be regenerated elsewhere in the cell.

Several well-known coenzymes include NAD+, NADP+, and FAD (oxidized forms that participate in redox reactions); coenzyme A (CoA) for acyl transfer; thiamine pyrophosphate (TPP) for decarboxylation; biotin for carboxylation reactions; pyridoxal phosphate (PLP) for amino acid metabolism; and folate derivatives and cobalamin-related cofactors for one-carbon transfers. Most of these derive from B vitamins such as niacin, riboflavin, pantothenate, biotin, thiamine, pyridoxine, and folate.

Mechanistically, coenzymes often shuttle electrons or groups between substrates, undergoing reversible chemical changes that accompany the turnover of the enzyme. After the reaction, the coenzyme is regenerated by other enzymes and cellular pathways to continue catalysis.

Biological importance: Coenzymes are indispensable for metabolism, energy production, and biosynthesis. Dietary vitamin deficiencies can impair enzyme function and lead to metabolic disorders. In research and industry, coenzymes are used to study enzyme mechanisms and in biotechnological applications.