[Glucose-6-phosphate dehydrogenase of Drosophila melanogaster: purification and some properties of normal and mutant enzyme forms].

Two isozymes of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) (G6PD) of Drosophila melanogaster encoded by allelic genes were purified 3000-fold by biospecific phosphocellulose chromatography, using NADP as the enzyme eluent. Electrophoretically fast isozyme A and slow isozyme B variants prove to contain identical subunits with molecular weight of 54000-55000. G6PD is shown to be a dimer. An antiserum directed to highly purified isozyme A does not inhibit the activity of both isozymes. The mutant forms of G6PD restoring the viability of flies without 6-phosphogluconate dehydrogenase show drastically increased Km values for NADP and/or glucose-6-phosphate. It was demonstrated for two mutations that a sharp (200-fold) magnification of Km value for the substrate followed by a considerable increase in the enzyme thermostability might not exert any essential influence on the Km value for NADP.