A multiple role for the coenzyme in the mechanism of action of 6-phosphogluconate dehydrogenase. The oxidative decarbosylation of 2-deoxy-6-phosphogluconate.

Abstract 6-Phosphogluconate dehydrogenase from Candida utilis catalyzes the oxidative decarboxylation of 2-deoxy-6-phosphogluconate. The 3-keto-2-deoxy-6-phosphogluconate, an intermediate of the reaction, is reduced to 2-deoxy-6-phosphogluconate and decarboxylated to 1-deoxyribulose 5-phosphate when incubated with the enzyme and TPNH. The decarboxylation process does not occur in the absence of the reduced coenzyme, which does not have, in this step, an oxidation-reduction role. Since TPNH also has a non-redox role in a tritium exchange reaction catalyzed by the enzyme, it appears that the coenzyme has a multiple role in the mechanism of action of 6-phosphogluconate dehydrogenase: a redox role in the dehydrogenation and another (or others) role(s) in the decarboxylation and tritium exchange reactions. The hydroxyl group present at carbon 2 of 6-phosphogluconate seems to have a dual role in the mechanism of action of the enzyme: one in the binding of the substrate to the enzyme, another in enhancing the decarboxylation of the dehydrogenation product. These findings are discussed with relations to the mechanism of action of isocitrate dehydrogenase and of the malic enzyme. The enzymatic oxidative decarboxylation of 2-deoxy-6-phosphogluconate is a new step for the metabolism of the metabolic inhibitor 2-deoxyglucose

Rose Bengal as a Specific Photosensitizer for a Histidine Residue at the Triphosphopyridine Nucleotide Binding Site of 6-Phosphogluconate Dehydrogenase

Rose Bengal is a potent inhibitor of 6-phosphogluconate dehydrogenase from Candida utilis and mediates the photoinactivation of the enzyme. The experiments reported in this paper indicate that photoinactivation occurs only when the dye is bound to the TPN binding site of the enzyme. Since the photoinactivation is correlated to the specific oxidation of only 2 residues of histidine, it can be assumed that this amino acid is located at the TPN binding site of 6-phosphogluconate dehydrogenase. These results are a new application of the technique of active site-specific photooxidation

Studies on the mechanism of action of the gluconate 6-phosphate dehydrogenase. The presence of a cysteine residue in the active center.

Abstract The role of the sulfhydryl groups in the gluconate 6-phosphate dehydrogenase has been studied. Nine cysteine residues have been detected by spectrophotometric titration with p-hydroxymercuribenzoate, but the reaction of only 3 of them is sufficient to inactivate the enzyme completely. Chlorodinitrobenzene acts even more specifically. Incorporation of 1.6 dinitrobenzene residues leads to enzyme inactivation. The amino acid residues involved in dinitrophenylation have been identified as cysteine. Gluconate 6-phosphate completely protects the enzyme against inactivation by chlorodinitrobenzene