Evidence for biochemical and physiological differences between enzyme genotypes in Drosophila melanogaster.

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Abstract
The in vivo flux of C through the pentose shunt is investigated as a function of different 6-phosphogluconate dehydrogenase (6Pgd) and glucose-6-phosphate dehydrogenase (G6pd) genotypes by using differential radioactive labeling of the C-1 and C-6 positions of glucose. Alternative 6Pgd-G6pd genotypes differ in relative in vivo C flux through the pentose shunt. The relative in vitro specific-activity differences between the 6PgdSS and 6PgdFF genotypes appear to be primarily responsible for these differences. The pentose-shunt activity is correlated with the rate of lipid synthesis. This correlation is consistent with the major metabolic function of the pathway, which is to produce NADPH for lipid synthesis. Different genotypes of 6Pgd are associated with measurable biochemical and physiological differences. Higher order phenotypic differences of this kind must be demonostrated to support the hypothesis that natural selection can discriminate among allozymes of a given genetic locus.