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 alpha subunit of the enzyme binds the substrates coenzyme A and phosphate, while succinate binding and specificity for either ATP or GTP is provided by different beta subunits. ATP + CoA + succinate = ADP + phosphate + succinyl-CoA CoA + GTP + succinate = GDP + phosphate + succinyl-CoA Carbohydrate metabolism; tricarboxylic acid cycle; succinate from succinyl-CoA (ligase route): step 1/1. Heterodimer of an alpha and a beta subunit. Different beta subunits determine nucleotide specificity. Together with an ATP-specific beta subunit, forms an ADP-forming succinyl-CoA synthetase (A-SCS). Together with a GTP-specific beta subunit forms a GDP-forming succinyl-CoA synthetase (G-SCS). Viable (PubMed:28017724). During development, results in delayed egg eclosion, reduced glycogen levels and extension of the third instar larval period but without change of the duration of the pupal period or final size of organ (PubMed:28017724). In the adult, results in defects in locomotor activity (PubMed:28017724). Results in disregulation of both glycolysis and the citric acid cycle (TCA) including accumulation of Succinyl-CoA and succinate, and reduction of GABA (PubMed:28017724). Belongs to the succinate/malate CoA ligase alpha subunit family.