Di- and triphosphopyridine nucleotide isocitric dehydrogenases in yeast.

The biological conversion of d-isocitric to a-ketoglutaric acid was established by the work of Martius and others (1-4). Adler et al. showed that, with extracts of acetone powders of animal tissues, triphosphopyridine nucleotide (TPN) is a specific coenzyme in the reaction and cited evidence for a similar specificity in yeast. Ochoa (5) synthesized oxalosuccinic acid, the intermediate postulated by Martius, and showed that the decarboxylation of this unstable p-keto acid is enzymatically catalyzed. He demonstrated further that in the presence of an enzyme preparation from pig heart and reduced TPN (TPNHZ) isocitric acid is formed from either oxalosuccinic acid or from cu-ketoglutaric acid and carbon dioxide. Grisolia and Vennesland (6) confirmed the fixation of carbon dioxide in the p-carboxyl carbon of isocitrate when isocitrate, NaHC403, cr-ketoglutarate, Mn++, and TPN were incubated with an extract of pigeon liver acetone powder. The conversion of isocitrate to a-ketoglutarate may therefore be formulated by the following reactions.