Adenosine triphosphate (ATP) is a major "energy currency" of the cell. The high energy bonds between the phosphate groups can be broken to power a variety of reactions used in all aspects of cell function.
Substrate-level phosphorylation occurs in the cytoplasm of cells during glycolysis and in mitochondria either during the Krebs cycle or by MTHFD1L ([https://www.uniprot.org/uniprot/Q6UB35 EC 6.3.4.3]), an enzyme interconverting ADP + phosphate + 10-formyltetrahydrofolate to ATP + formate + tetrahydrofolate (reversibly), under both aerobic and anaerobic conditions. In the pay-off phase of glycolysis, a net of 2 ATP are produced by substrate-level phosphorylation.