Purification and properties of wild-type and mutant glucose 6-phosphate dehydrogenases and of 6-phosphogluconate dehydrogenase from Drosophila melanogaster.

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Abstract
Glucose-6-phosphate dehydrogenase was purified to a homogeneous state from D. melanogaster imagos made homozygous for the X chromosome of a mutant male, which showed 2 bands of enzyme activity on polyacrylamide gels and from Oregon R flies similarly made homozygous, which showed only 1 major band; their properties were compared with respect to MW, pH optimum, specific activity, Km values and sensitivity to p-chloromercuribenzoate, MgCl2, dehydroepiandrosterone, heat and anti-Oregon R glucose-6-phosphate dehydrogenase antibody. The fast and slow bands of mutant enzyme had MW of 115,000 and 283,000, respectively, while the wild-type enzyme had a MW of 120,000. Treatment with sodium dodecyl sulfate cleaved the 3 enzymes into a subunit having a MW of 69,000. This suggests that the slow and fast bands of the mutant enzyme represent tetramers and dimers of single polypeptides, respectively. Since the mobility of the fast mutant enzyme was the same as that of wild-type enzyme, it is inferred that the mutation resulted in a change of the quaternary structure of enzyme, without affecting its net charge in this particular instance. The mutant enzyme was more heat-stable than the wild-type enzyme, but they did not differ in other respects. 6-Phosphogluconate dehydrogenase was also purified to a homogeneos state from the wild and mutant flies. No difference was found between the 2 strains of flies with respect to several parameters used.