Succinyl phosphonate is an inhibitor of the α-ketoglutarate dehydrogenase. In Vitro: Succinyl phosphonate is an α-Ketoglutarate phosphoanalogue. It is found to be an effective inhibitor of α-ketoglutarate oxidative decarboxylation, catalyzed by both muscle and bacterial α-ketoglutarate dehydrogenase complexes, as well as muscle α-ketoglutarate dehydrogenase^[1]. At a concentration of 0.01 mM, succinyl phosphonate completely inhibits isolated brain KGDHC even in the presence of a 200-fold higher concentration of its substrate. In cultured human fibroblasts, 0.01 mM succinyl phosphonate produced 70% inhibition of α-ketoglutarate dehydrogenase complex. DESP and TESP are also inhibitory in the cell system, but only after preincubation, suggesting the release of their charged groups by cellular esterases^[2]. Succinyl phosphonate inhibits 2-Oxoglutarate dehydrogenase , the first rate-limiting component of the mitochondrial multi-enzyme complex of oxidative decarboxylation of 2-oxoglutarate, in a highly selective and efficient manner^[3].