[Possible mechanisms of regulating glucose-6-phosphate dehydrogenase activity by an excess of substrate and coenzyme].
The kinetics of glucose 6-phosphate oxidation by glucose 6-phosphate dehydrogenase from wheat seeds was studied at pH 6-11 within a broad interval of the glucose 6-phosphate and NADH concentrations. A high substrate concentration (over 4-6 mM) activated the enzyme within the pH range studied; the excess of NADH inhibited glucose 6-phosphate dehydrogenase at pH 6.0-9.5. The enzyme's active site groups with pK of 7.2, 8.0, and 9.0 were shown to be involved in the substrate binding in the enzyme-substrate complexes. The ionization of the groups with pK 8.0 and 9.5 appeared to affect the catalytic activity of the enzyme. The deprotonation of the group with pK 9.5 increased the reaction rate, whereas its protonation favored enzyme inhibition by high NADH concentrations.
Rogozhin
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D001665:Binding Sites; D002384:Catalysis; D004789:Enzyme Activation; D019298:Glucose-6-Phosphate / Q000378:metabolism*; D005954:Glucosephosphate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D013379:Substrate Specificity; D014908:Triticum / Q000201:enzymology
D009249:NADP; D019298:Glucose-6-Phosphate; D005954:Glucosephosphate Dehydrogenase