1. Lafayette Clinic and Wayne State University School of Medicine, Detroit, Michigan.

Abstract

IN mammals, lactic dehydrogenase (LDH) has five molecular forms which show species and tissue specific patterns by starch-gel electrophoresis¹. These molecular forms appear to be tetramers of two different polypeptide sub-units in their five possible combinations^2,3. The two types of sub-units have been termed 'A' and 'B' (ref. 2), or 'M' and 'H' referring to their predominance in skeletal muscle and heart respectively³. The M(uscle) type of lactic dehydrogenase is best suited for anaerobic metabolism and the H(eart) type is best suited for oxidative metabolism^3,4. Since glycolysis or anaerobic metabolism is phylogenetically more ancient that aerobic metabolism⁵, a shift in certain tissues from M LDH to H LDH would be expected during the phylogenetic development of higher animals. From a comparative study of lactic dehydrogenases in a small series of vertebrate brains, Bonavita and Guarneri⁶ provided evidence that this trend occurred during the emergence of warm-blooded vertebrates. The present communication provides evidence that such a shift was still occurring during the evolution of the order Primates.