Succinyl-CoA synthetase functions in the citric acid cycle (TCA), coupling the hydrolysis of succinyl-CoA to the synthesis of either ATP or GTP and thus represents the only step of substrate-level phosphorylation in the TCA. The beta subunit provides nucleotide specificity of the enzyme and binds the substrate succinate, while the binding sites for coenzyme A and phosphate are found in the alpha subunit. Can use either ATP or GTP, but prefers ATP. It can also function in the other direction for anabolic purposes, and this may be particularly important for providing succinyl-CoA during anaerobic growth when the oxidative route from 2-oxoglutarate is severely repressed. ATP + CoA + succinate = ADP + phosphate + succinyl-CoA Binds 1 Mg(2+) ion per subunit. Exhibits two interesting properties: 'substrate synergism', in which the enzyme is most active for the catalysis of its partial reactions only when all the substrate-binding sites are occupied, and 'catalytic cooperativity' between alternating active sites in the tetramer, whereby the interaction of substrates (particularly ATP) at one site is needed to promote catalysis at the other. kcat is 2684 min(-1) with ATP as substrate and 1471 min(-1) with GTP as substrate. Optimum pH is 7.4. Carbohydrate metabolism; tricarboxylic acid cycle; succinate from succinyl-CoA (ligase route): step 1/1. Heterotetramer of two alpha and two beta subunits. Succinyl-CoA synthetase (SCS) of E.coli catalyzes its reaction via three steps that involve phosphoryl enzyme and enzyme-bound succinyl phosphate as intermediates. Belongs to the succinate/malate CoA ligase beta subunit family.