Enzymatic Potential for Preformed Purine Metabolism in Hepatomas With Different Growth Rates

The activities of five enzymes associated with purine reutilization and interconversion were determined in hepatomas with different growth rates. The activities of hypoxanthine and adenine phosphoribosyltransferases in this spectrum of hepatomas ranged from 50 to 170% of normal control liver. The ratio of activity of hypoxanthine phosphoribosyltransferase to adenine phosphoribosyltransferase was moderately reduced in hepatomas when compared to that in normal liver. No consistent alteration in the activity of guanine aminohydrolase was observed within the spectrum of these hepatomas. The activity of xanthine oxidase in hepatomas was either normal or significantly reduced when compared to the levels of activity exhibited by normal controlliver. Only purine nucleoside phosphorylase activity was consistently and significantly altered in ali hepatomas. This enzyme activity was reduced to levels of 9–42% of those in normal liver. Purine nucleoside phosphorylases from hepatoma and normal liver were similar, as judged by their behavior on DEAE-cellulose column, polyacrylamide gel electrophoresis, and kinetic analysis. Although several of the enzyme activities were markedly reduced in the most rapidly growing tumors, the enzymes did not exhibit any correlation with tumor growth rate, and their activity in host liver was not appreciably changed by the growing tumor.