Characterization of Glycogen Synthetases and Phosphorylases in Transplantable Rat Hepatomas1

A study of the chemical and kinetic properties of a series of transplantable, chemically induced rat hepatomas has revealed profound alterations in isozyme patterns of glycogen synthetase and phosphorylase. Highly differentiated, slow-growing hepatomas retain the liver-type isozymes, but with decreased differentiation and increased growth rate these are largely or entirely replaced by nonhepatic isozymes. The phosphorylase of poorly differentiated hepatomas was a third form, shown by isoelectric focusing and by immunochemical criteria to be different from either the liver or muscle isozymes. This form was also present in 21-day fetal liver, together with the adult liver isozyme. All of the hepatomas contained the phosphatases and kinases that interconvert the a and b forms, and preliminary data indicate that the synthetase phosphatase of the poorly differentiated hepatomas also is different from the liver phosphatase. Total synthetase activity was high in liver and muscle, lower in the wellto highly differentiated hepatomas, and very low in poorly differentiated tumors, except for the Novikoff ascites hepatoma, the only one of the poorly differentiated tumors that stored appreciable glycogen. In all tissues, b form predominated. Total phosphorylase activity was highest in muscle, predominantly in the b form; lower in liver; and still lower in tumors. There was no correlation between the activity of tumor phosphorylase and the degree of differentiation or the storage of glycogen, and most of the liver and hepatoma phosphorylase was in the a form.