A molecule of guanosine triphosphate is synthesized from guanosine diphosphate and phosphate at the cost ofhydrolyzing succinyl CoA to succinate and CoA. This constitutes substrate-level phosphorylation, and, in contrast to oxidative phosphorylation, this is the only reaction in the citric acid cycle that directly yields a high-energy phosphate bond. The sequence of reactions from alpha-ketoglutarate to succinate is catalyzed by the a -ketoglutarate dehydrogenase complex and succinyl-CoA synthetase, respectively.