Coenzima

A coenzyme is an organic molecule that participates in enzyme-catalyzed reactions and is required for the enzyme to function. The protein part of the enzyme is called an apoenzyme, and when it binds a coenzyme the complex becomes a holoenzyme. Coenzymes are usually not permanently attached; some act as prosthetic groups, while others bind loosely and are reused after the reaction.

Coenzymes are typically derived from vitamins and serve as carriers for electrons, acyl groups, or other functional groups during catalysis. They enable a wide range of chemical transformations that the amino acid-based active site alone could not accomplish. Coenzymes are distinct from inorganic cofactors such as metal ions (for example, Mg2+ or Zn2+), which can also be essential for enzyme activity.

Common examples of coenzymes include NAD+ and NADH, NADP+ and NADPH (oxidation-reduction reactions), FAD and FMN (electron transfer), and Coenzyme A (acyl group transport, forming acetyl-CoA). Others include biotin (carboxylation reactions), thiamine pyrophosphate (TPP, decarboxylation and transfer reactions), and pyridoxal phosphate (PLP, amino group transfer). Many coenzymes function as carriers of specific chemical groups or electrons during metabolic pathways such as glycolysis, the citric acid cycle, fatty acid oxidation, and amino acid metabolism.

Deficiencies or impairments in vitamin availability can disrupt coenzyme formation and enzyme activity, leading to metabolic disorders. Understanding coenzymes illuminates how vitamins support energy production and biosynthesis in cells.