Effect of cytidine on purine nucleotide formation in ascites tumor cells in vitro.

Abstract

The stimulation of purine nucleotide synthesis by cytidine and glucose in Ehrlich ascites tumor cells in vitro appears to be due to the utilization of the ribose moiety. Thus, these compounds stimulated nucleotide formation from precursors which depended on linkage with a pentose moiety but not from those already linked to pentose. When uniformly labeled cytidine was incubated with the cells, 14 C was incorporated into the ribose or deoxyribose moiety of the purine nucleotides of the acid-soluble, RNA, and DNA fractions. It was demonstrated that the incorporation of 14 C from uniformly labeled cytidine into the ribose moiety of ATP was sufficient to account for the increase in [ 14 CC]adenine incorporation into ATP when cytidine was added. When cytidine and phosphate were incubated with the high-speed supernatant fraction from a homogenate of these cells, uridine, uracil and orcinol-reacting (non-pyrimidine linked) ribose were produced. It was suggested that cytidine is first deaminated to uridine, which in turn is split by uridine phosphorylase to produce ribose 1-phosphate, which is then available for utilization in purine nucleotide formation.