Which reaction generates ATP through substrate-level phosphorylation rather than through a proton gradient?

Core Concept

In substrate-level phosphorylation, an enzyme transfers a phosphate directly from a high-energy substrate onto ADP or GDP. The succinyl-CoA synthetase step releases enough energy when succinyl-CoA loses coenzyme A to phosphorylate GDP, forming GTP that readily converts to ATP. This mechanism needs no membrane gradient and continues even when the electron transport chain is idle. Comparable steps occur in glycolysis at 1,3-bisphosphoglycerate and phosphoenolpyruvate.