6-Phosphogluconate dehydrogenase from Drosophila melanogaster. I. Purification and properties of the A isozyme.

6-Phosphogluconate dehydrogenase is evident at all developmental stages of Drosophila melanogaster. The activity level is highest in early third instar larvae and declines to a lower, but relatively constant, level at all later stages of development. The enzyme is localized in the cytosolic portion of the cell. The A-isozymic form of 6-phosphogluconate dehydrogenase was purified to homogeneity and has a molecular weight of 105,000. The enzyme is a dimer consisting of subunits with molecular weights of 55,000 and 53,000. For the oxidative decarboxylation of 6-phosphogluconate the Km for substrate is 81 muM while that for NADP+ is 22.3 muM. The optimum pH for activity is 7.8 while the optimum temperature is 37 C.