Isozyme patterns of glycogen phosphorylase in rat tissues and transplantable hepatomas

Isozyme patterns of glycogen phosphorylase in the Morris and Yoshida hepatomas were compared electrophoretically and immunochemically with those in rat tissues during development. A 3rd phosphorylase isozyme, observed previously in hepatomas and fetal tissues by isoelectric focusing and by immunochemical titration, was also separated by polyacrylamide disc gel electrophoresis. It was observed commonly in various rat hepatomas, together with variable activities of the liver type, depending on the degree of differentiation. This isozyme is nearly the sole type in placenta and early embryo, and in liver and skeletal muscle it is replaced during fetal development with the organ-specific liver and muscle type. In adult rat brain the fetal type is retained at low levels, together with the muscle type. In kidney, spleen, testis, uterus, lung, and stomach, the fetal type is present together with the liver type. This isozyme in hepatomas and adult brain is identical with the fetal-type, as determined by Ouchterlony double diffusion and activity inhibition tests. Thus, it is considered to be a prototype whose appearance in hepatomas is one of many known examples of fetal protein expression in cancer. In some poorly differentiated hepatomas, the liver-type isozyme migrated slightly more slowly in polyacrylamide gel but could not be distinguished from the liver isozyme immunochemically.