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

Abstract

Glucose 6-phosphate dehydrogenase was purified to a homogeneous state from Drosophila melanogaster imagoes made homozygous for the X chromosome of a mutant male which showed two bands of enzyme activity on polyacrylamide gels as well as from Oregon R flies similarly made homozygous which showed only one major band, and their properties were compared with respect to molecular weight, 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 molecular weights of 115, 000 and 283, 000, respectively, while the wild-type enzyme had a molecular weight of 120, 000. Treatment with sodium dodecyl sulfate cleaved the three enzymes into a subunit having a molecular weight 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 homogeneous state from the wild and mutant flies. No difference was found between the two strains of flies with respect to several parameters used.