Regulation of Glucose-6-Phosphate Dehydrogenase inBrevibacterium flavum

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Abstract
NADP-Specific G6P dehydrogenase was partially purified from Brevibacterium flavum. Its activity, with an optimum pH of 7.5, was stabilized by KC1 or Mg2+ and inhibited by diamide, a sulf-hydryllreagent. It was also inhibited by oxaloacetate, FBP, PRPP, acetyl-CoA, Ru5P, xylulose 5-phosphate and NADPH. Among them, oxaloacetate showed the strongest inhibition. The concentration of oxaloacetate giving 50% inhibition was 0.09 mm. The inhibitions by oxaloacetate, FBP, PRPP, and NADPH were non-competitive, mixed, and competitive for both the substrates, respectively. Oxaloacetate in combination with FBP, PRPP, or Ru5P inhibited the activity cumulatively. The sensitivities to the oxaloacetate, FBP, and PRPP inhibitions were lost on ammonium sulfate treatment, whereas that to NADPH inhibition was not affected at all. The inhibition by oxaloacetate was specific to glutamate-producing bacteria belonging to the genera, Brevibacterium and Corynebacterium, in contrast to those by FBP and PRPP, which were found in almost all bacteria tested. G6P dehydrogenase in B. flavum was induced by glucose when it was cultured on acetate, succinate, or glutamate.