Nucleoside metabolism in ehrlich ascites tumor cells: Phosphorolysis of purine nucleosides

The metabolism of purine nucleosides was studied in both intact Ehrlich ascites carcinoma cells and in cell-free extracts obtained from these cells. Tracer experiments with intact cells indicate the formation of inosine and hypoxanthine from adenosine and of hypoxanthine from inosine. With cell-free extracts the initial reaction is the phosphorolytic cleavage of the nucleosides to free purine base plus ribose 1-phosphate, except in the case of adenosine, which is first deaminated to inosine. The enzyme(s) responsible for the phosphorolysis is apparently specific for purine nucleosides and acts on inosine, guanosine, and xanthosine. The enzyme(s) can be partially purified from cell extracts by fractionation with ammonium sulfate. The ribose 1-phosphate produced was shown to be the α-isomer, and evidence was obtained for its further metabolism via the pentose phosphate pathway.