Substratphosphorylierung

Substrate phosphorylation, commonly called substrate-level phosphorylation, is a biochemical process in which a phosphate group is transferred directly from a high-energy phosphorylated substrate to ADP (or GDP) to form ATP (or GTP). This occurs within metabolic pathways and does not require an electron transport chain or a proton motive force.

In glycolysis, energy-rich intermediates such as 1,3-bisphosphoglycerate and phosphoenolpyruvate donate phosphate groups to ADP, yielding ATP in two reaction steps catalyzed by phosphoglycerate kinase and pyruvate kinase. In the citric acid cycle, succinyl-CoA synthetase converts succinyl-CoA to succinate, generating GTP (which can be converted to ATP) directly. These reactions contrast with oxidative phosphorylation, where ATP is produced indirectly via the mitochondrial electron transport chain and chemiosmosis.

Substrate-level phosphorylation provides a rapid, direct means of generating ATP and is especially important under low-oxygen conditions or when oxidative phosphorylation capacity is limited. While it contributes a modest portion of cellular ATP overall, it is essential for certain tissues and metabolic states. The term is distinct from phosphorylation events in signaling pathways, where kinases modify proteins or other molecules rather than generating ATP.