Purine-metabolizing Enzymes in Normal Rat Liver Nandovikoff Hepatoma^* †

The levels of activity and the intracellular distribution of 5′-nucleotidase, nucleoside phosphorylase, adenosine deaminase, guanase, adenase, xanthine oxidase, and uricase have been determined in normal liver and in Novikoff hepatoma. The activities of 5′-nucleotidase, nucleoside phosphorylase, guanase, and adenase were greatly diminished, whereas that of adenosine deaminase was increased in the transplanted hepatoma as compared with normal liver. Xanthine oxidase and uricase activities could not be demonstrated in the tumor transplant. The intracellular distributions of the enzymes studied were similar in both the liver and hepatoma tissues. These findings suggest that the catabolism of purines and purine derivatives is not only deeply impaired but completely blocked at the stage of xanthine and hypoxanthine.