Further studies on the properties and assay of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase of rat liver

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Abstract
Both glucose 6-phos-phate and 6-phosphogluconate dehydrogenases are present exclusively in the soluble fraction of disintegrated liver. Conditions for the assay of these dehydrogenases in rat liver are descr., and a unit of activity defined as the quantity of enzyme which at 20[degree] reduces 0.01[mu] mole triphosphopyridine nucleotide per minute. The mean values of glucose 6-phosphate dehydrogenase activity, detd. at pH 7.6, and of 6-phosphogluconate dehydrogenase activity, detd. at pH''s 7.6 and 9.0, were respectively 46 [plus or minus] 3,59 [plus or minus] 8 and 147 [plus or minus] 10 units/g. liver in malc rats. All these levels were consistently higher in femalcs. Both dehydrogenases are activated by Mg++, Ca++ and Mn++ and inhibited by Hg++. 6-Phospho-gluconate dehydrogenase is also inhibited by Cu++ and Zn++. Evidence is presented that the activity of 6-phosphogluconate dehydrogenase is dependent on the presence of active sulfhydryl groups. Adenosine triphosphate acts as a competitive inhibitor of 6-phosphogluconate dehydrogenase but not of glucose 6-phosphate dehydrogenase.