Regulation of 6-Phosphogluconate Dehydrogenase in Brevibacterium flavum

概要

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6PG dehydrogenase (EC 1.1.1.44), partially purified from Brevibacterium flavum, was specific to NADP+, stabilized by KCl, and had an optimum pH of 7.5 to 8.0. Its activity was inhibited by FBP, PRPP, GAP, oxaloacetate, E4P, acetyl-CoA, Ru5P, and NADPH, among which, FBP showed the.strongest inhibition. The concentrations of the latter giving 50 and 100% inhibition were 0.07 and 1.0 mM, respectively. Inhibition by FBP, PRPP, and E4P was competitive to 6PG but not to NADP+. Homotropic interaction of 6PG was observed in the presence of FBP and the Hill coefficient was estimated to be 1.6. Inhibition by the reaction products, Ru5P and NADPH, was mixed and noncompetitive to 6PG and noncompetitive and mixed to NADP+, respectively. Combination of acetyl-CoA with FBP or PRPP inhibited the enzyme synergistically and that of acetyl-CoA with GAP or Ru5P did cumulatively. The sensitivities of the enzyme to the FBP, PRPP, acetyl-CoA, oxaloacetate, and E4P inhibitions were lost with ammonium sulfate treatment. The enzyme was induced by gluconate. Cells grown on gluconate did not contain an FBP-insensitive and NAD-specific enzyme at all.
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