mostly consuming tissues such as heart and brain have more atp-specific succinyl-coa synthetase (atpscs), while synthetic tissues such as kidney and liver have the more gtp-specific form (gtpscs). kinetics analysis of atpscs from the breast muscle of pigeons and gtpscs from pigeon liver showed that their apparent michaelis constants were similar for coa, but different for the nucleotides, phosphate, and succinate. the largest difference was for succinate: kapp of atpscs = 5mm versus that of gtpscs = 0.5mm.