Comparative properties of three forms of glucose-6-phosphate dehydrogenase in Drosophila melanogaster

Three alleles of the Zw locus of Drosophila melanogaster--ZwA, ZwB, and Zwlol--apparently code for dimeric, tetrameric, and monomeric forms of glucose-6-phosphate dehydrogenase (G6PD), respectively. The three forms of G6PD are characterized by different apparent Km values for glucose-6-phosphate but similar apparent Km values for NAPD+. When high concentrations of NAPD+ were added to enzyme preparations, the ZwA and Zwlol forms of G6PD assumed tetrameric and dimeric properties, respectively. Although Zwlol adults exhibit little G6PD activity, they maintain levels of G6PD-antigen comparable to those in ZwA and ZwB adults. Thus the low level of G6PD activity in Zwlol individuals cannot be explained as the consequence of lack of synthesis of the G6PD subunit.