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. ATP + CoA + succinate = ADP + phosphate + succinyl-CoA Binds 1 Mg(2+) ion per subunit. Carbohydrate metabolism; tricarboxylic acid cycle; succinate from succinyl-CoA (ligase route): step 1/1. Heterotetramer of two alpha and two beta subunits. Belongs to the succinate/malate CoA ligase beta subunit family.