DIRECT MEASUREMENT OF INVIVO FLUX DIFFERENCES BETWEEN ELECTROPHORETIC VARIANTS OF G6PD FROM DROSOPHILA-MELANOGASTER

Demonstrating that naturally occurring enzyme polymorphisms significantly impact metabolic pathway flux is a fundamental step in examining the possible adaptive significance of such polymorphisms. In earlier studies of the glucose-6-phosphate dehydrogenase (G6PD) polymorphism in Drosophila melanogaster, we used two different methods, exploiting both genotype-dependent interactions with the 6Pgd locus, and conventional steady-state kinetics to examine activity differences between the two common allozymes. In this report we use 1-C-14- and 6-C-14-labeled glucose to estimate directly genotype-dependent flux differences through the pentose shunt. Our results show the G6pd(A) genotype possesses statistically lower pentose shunt flux than G6pd(B) at 25-degrees. We estimate this to be about a 32% reduction, which is consistent with the two former studies. These results reflect a significant responsiveness of pentose shunt flux to activity variation at the G6PD-catalyzed step, and predict that the G6PD allozymes generate a polymorphism for pentose shunt flux.