An intermediate of the Krebs cycle that consists of succinic acid linked to coenzyme A by a high-energy thioester bond. Succinyl CoA synthetase can reversibly convert succinic acid to succinyl-CoA. Succinyl-CoA can also be synthesized from alpha-ketoglutarate by alpha-ketoglutarate dehydrogenase and from methylmalonyl-CoA by methylmalonyl-CoA mutase. Succinyl-CoA is converted to aminolevulinic acid for heme synthesis by aminolevulinate synthase.