[Purification and various biochemical and immunological properties of wild and mutant forms of Drosophila melanogaster 6-phosphogluconate dehydrogenase]

Abstract

A 1500--2000-fold purification procedure using substrate elution from phosphocellulose is described for two isozymes of 6-phosphogluconate dehydrogenase (6PGD) coded for by the corresponding allelic genes. Taking into account the data of gel filtration and of SDS polyacrylamide gel electrophoresis both isozymes are shown to be dimers containing identical polypeptides of mol. weight 50 000. Antisera against the highly purified sample of 6PGD, inactivated by lyophilization completely inhibited the enzyme activity. Antigens reacting to antisera were revealed by Ouchterlony immunodiffusion tests in extracts of flies carrying the wild type or mutant Pgd allele, coding for 6PGD. In addition to 6PGD antigen (antigen 1) another protein (antigen 2) which shared no common antigenic precipitative determinants with the antigen 1 was revealed in extracts of the normal flies. Antigen 2 was demonstrated also in the six different mutants which expressed zero level of 6PGD activity and had no antigen 1. Mol weight of a 6PGD subunit and of antigen 2 purified by immobilized antibodies were shown to be identical by SDS-polyacrilamide gel electrophoresis. A transformation of "antigen 2" to "antigen 1" was performed by treatment of the former in 2% SDS-mercaptoethanol solution. As a result of SDS treatment no changes of antigenic properties of the inactivated and dissociated 6PGD dimers were observed in immunodiffusion tests.