Phosphogluconate Dehydrogenase Polymorphism in British Wild Rats

Abstract

PHOSPHOGLUCONATE dehydrogenase (PGD) has been found to be polymorphic in several species, including the rat, when studied by starch gel electrophoresis¹. Investigation of this enzyme in the rat revealed three distinct electrophoretic phenotypes, giving respectively a slow migrating component, the S phenotype, a fast migrating component, the F type, and the SF phenotype, giving a triplet of electrophoretic bands comprising both the slow and the fast migrating bands, and also a strongly staining band with intermediate mobility². As in all mammals, rat PGD was found to be controlled by an autosomal gene locus. The S phenotype seemed to be a consequence of a homozygous PGD genotype, PGD^SPGD^S. The SF and F types, commonly found in wild but not laboratory rats, were considered to be the product of genotypes PGD^FPGD^S and PGD^FPGD^F respectively. Each (presumably allelic) gene was thought to code for one type of polypeptide subunit (either s or f) and the triplet zymogram in heterozygotes was considered to be the result of the random association in pairs of subunits of these two varieties, thus producing three dimeric oligomers: ss, sf and ff. The three types of rat PGD were not found to differ from each other with respect to optimal pH, K_M and stability.