Molecular Size Studies on 6-Phosphogluconate Dehydrogenase

Abstract

GENETICALLY determined electrophoretic variants of 6-phosphogluconate dehydrogenase (6-PGD) have been found in man and rat¹, pigeon², deer mouse³, and the fruit fly⁴. In all five species the heterozygous phenotype contains the two parental enzyme forms plus a third 6-PGD of intermediate electrophoretic mobility on starch gel. In experiments with partially purified 6-PGD of Drosophila melanogaster we have recovered the intermediate PGD I^AB after in vitro treatment of the two parental types, PGD A and PGD B, with propanedithiol⁵. Although this is good evidence that the enzyme is composed of two or more sub-units, the remote possibility that the two parental enzymes polymerize to form the intermediate PGD I^AB was not excluded. We now report further experiments bearing on the molecular structure and size of the enzyme.