Mammalian pyruvate kinase hybrid isozymes: tissue distribution and physiological significance

The purpose of this study was to examine the pyruvate kinase isozymic patterns of a wide variety of tissues from rats and mice, particularly regarding hybrid isozymes. For these studies, we employed longer electrophoresis times than used in most earlier studies in order to improve the resolution of closely spaced bands. The tissue distributions of types K, L, and M pyruvate kinases were found to be approximately the same as those reported earlier for rats and other mammals. In addition, K-M hybrids could be detected in most tissues examined in relative quantities which differed from one tissue to another in the same organism, in corresponding tissues from different species, and within a single tissue during development. Hybrid isozymes containing type L subunits occur in only a few tissues of either the fetus or the adult of either animal. In earlier studies utilizing L-M hybrid isozymes produced in vitro, we showed that the kinetic properties of a given subunit are profoundly affected by the nature of its neighbors within the tetramer (Dyson and Cardenas, ['73] J. Biol. Chem., 248: 8482-8488). Based on these altered kinetic properties, we suggest that there is little need for anorganism to suppress completely the gene activity for one subunit type of pyruvate kinase during the synthesis of larger quantities of a second subunit type.