Substrate-level phosphorylation

Substrate-level phosphorylation forms ATP or another nucleoside triphosphate by transferring a phosphate group directly from a high-energy metabolic intermediate to a nucleoside diphosphate.

Phosphoglycerate kinase: An enzyme that transfers phosphate from 1,3-bisphosphoglycerate to ADP, producing ATP and 3-phosphoglycerate. It catalyzes the first ATP-producing substrate-level phosphorylation in glycolysis.
Adenosine diphosphate: A nucleotide that accepts a phosphate group to form adenosine triphosphate. ADP is the phosphate acceptor in the defining ATP-forming reactions.
Oxidative phosphorylation: ATP production driven by electron transport and a proton gradient across a membrane. Unlike direct transfer from a metabolic intermediate, it depends on chemiosmosis.
Fermentation: A metabolic process that regenerates NAD⁺ without an electron transport chain, often producing organic end products. Fermenting cells rely on glycolytic substrate-level phosphorylation for ATP.
Pyruvate kinase: An enzyme that transfers phosphate from phosphoenolpyruvate to ADP, producing ATP and pyruvate. Its reaction completes glycolysis with a second direct phosphate transfer to ADP.
Guanosine diphosphate: A nucleotide that accepts a phosphate group to form guanosine triphosphate. Succinyl-CoA synthetase can phosphorylate GDP instead of ADP.
Photophosphorylation: ATP production powered by light-driven electron transport and a proton gradient in photosynthetic membranes. It uses light and membrane energetics rather than direct transfer from a substrate.
Anaerobic respiration: Respiration that uses an electron acceptor other than oxygen in its terminal electron-transfer step. It can combine substrate-level ATP production with electron-transport-based energy conservation.
Succinyl-CoA synthetase: An enzyme that couples succinyl-CoA conversion to succinate with formation of GTP or ATP. It generates a nucleoside triphosphate during the citric acid cycle.
Phosphoryl group transfer potential: The tendency of a phosphorylated compound to transfer its phosphoryl group, often assessed through standard free-energy change. ATP formation requires a donor whose phosphate transfer can drive the reaction energetically.

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