Genetic variation in supernatant malate dehydrogenase of birds and reptiles

Electrophoretic variants of supernatant malate dehydrogenase were found within populations of a brid (Pitohui kirhocephalus) and of a reptile (Chrysemys picta). Upon starch gel electrophoresis, tissue extracts from variant individuals exhibit three equally spaced bands of supernatant malate dehydrogenase activity, whose staining intensities are approximately in a ratio of 1:2:1. Normal individuals, on the other hand, exhibit a single major band which is identical in mobility with the fastest of the variant bands. Immunological tests show that the Pitohui and Chrysemys enzymes are homologous with the well-characterized supernatant malate dehydrogenase of the domestic chicken. These results along with those obtained on other species imply that birds, reptiles, mammals, and certain invertebrates may possess a single locus coding for supernatant malate dehydrogenase. By contrast, some species of fishes and invertebrates possess multiple loci for this enzyme. A notable feature of the present investigation was the use of phenoxyethanol for extracting malate dehydrogenases from bird tissues. Extracts were prepared simply by soaking tissue in an aqueous solution of this reagent, no homogenization or centrifugation being required.This investigation was supported by funds from a research grant awarded by the National Science Foundation (GB-13119) and a U.S. Public Health Service Training Grant (GM 31-12).