GAPDH

GAPDH, or glyceraldehyde-3-phosphate dehydrogenase, is a key enzyme of glycolysis that catalyzes the oxidation and phosphorylation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, using NAD+ as an electron acceptor and producing NADH. It is typically a cytosolic enzyme that functions as a homotetramer; each subunit is around 335 amino acids and about 36 kDa.

The enzyme contains an NAD+-binding domain and a catalytic domain. Its active-site cysteine residue is essential for catalysis, enabling hydride transfer from glyceraldehyde-3-phosphate to NAD+. The reaction links glycolysis to energy production and provides substrates for downstream ATP generation through substrate-level phosphorylation.

In humans and many organisms, GAPDH is encoded by a single GAPDH gene and is abundantly expressed in many tissues, often serving as a housekeeping gene in molecular studies. Despite its cytosolic, metabolic role, GAPDH is found in other cellular compartments under certain conditions, including the nucleus and mitochondria, reflecting a range of non-glycolytic activities.

GAPDH has been described as a “moonlighting” protein because it participates in processes beyond glycolysis, such as regulation of gene expression, RNA transport, DNA repair, and apoptosis. These functions can be modulated by post-translational modifications and cellular redox status, which can also influence its localization and activity.

Clinical and research relevance includes its widespread use as a reference gene in transcript studies; however, expression can vary with metabolic state, stress, or cancer, so validation is advised. In cancer, GAPDH expression and glycolytic flux often rise as part of the Warburg effect, linking metabolism to disease progression. Post-translational modifications and redox regulation further modulate GAPDH function in health and disease.