THE SYNTHESIS OF EXTRACELLULAR RIBONUCLEOSIDES BY ASCITES TUMOR CELLS IN VITRO

Abstract

Ehrlich ascites carcinoma cells in vitro converted extracellular hypoxanthine to extracellular inosine if uridine or guanosine was provided in the medium at the rate of 20–30 μmoles per milliliter of cells per hour. The synthesis of external uridine also took place when cells were incubated with uracil and a purine ribonucleoside, but at a lower rate than that of inosine. Intact Ehrlich ascites cells catalyzed an exchange between labelled uracil and uridine when both were present in the incubation medium.The synthesis of the extracellular ribonucleoside appeared to be mediated by ribonucleoside phosphorylases and to take place by the transfer of the ribosyl group from a donor ribonucleoside to an acceptor base.