The effect of substitution at C-2 of d-glucose 6-phosphate on the rate of dehydrogenation by glucose 6-phosphate dehydrogenase (from yeast and from rat liver)

1. The deoxyfluoro-d-glucopyranose 6-phosphates are substrates for both yeast and rat liver glucose 6-phosphate dehydrogenase. 2. The V(max.) values (relative to d-glucose 6-phosphate) were determined for a series of d-glucose 6-phosphate derivatives substituted at C-2. The V(max.) values decreased with increasing electronegativity of the C-2 substituent. This is consistent with a mechanism involving hydride-ion transfer. 3. 2-Deoxy-d-arabino-hexose 6-phosphate (2-deoxy-d-glucose 6-phosphate) showed substrate inhibition with the yeast enzyme but not with the rat liver enzyme. 4. 2-Amino-2-deoxy-d-glucose 6-phosphate (d-glucosamine 6-phosphate) was a substrate for the yeast enzyme but a competitive inhibitor for the rat liver enzyme. 5. Lineweaver-Burk plots for the d-glucose 6-phosphate derivatives with yeast glucose 6-phosphate dehydrogenase were biphasic.