Purine and phosphoribosylpyrophosphate synthesis in differentiating murine virus‐induced erythroleukemic cells in vitro

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Abstract
Phosphoribosylpyrophosphate synthetase activity was determined in Friend virus‐inducted erythroleukemic cells in culture, stimulated to differentiate in the presence of dimethylsulfoxide. The activity of phosphoribosylpyrophosphate synthetase did not decrease in cells which had acquired the specialized function of hemoglobin synthesis, nor was the phosphoribosylpyrophosphate content of untreated erythroleukemic cells significantly different from that of cultures exposed to dimethylsulfoxide for 96 hours.However, the rate of the early steps of de novo purine biosynthesis as measured by the incorporation of [1‐14C] glycine and [1‐14C] formate into formyglycinamide ribonucleotide, was significantly lower in differentiating cell cultures. The addition of glutamine or ammonia increased glycine incorporation of control cultures, but failed to do so in treated cultures. In the course of the normal development of erythrocytes in vivo, phosphoribosylpyrophosphate synthetase activity is preserved, while the capacity to synthesize purines de novo is lost, as is the activity of the phosphoribosyl‐l‐amine synthesizing enzymes. Our present study suggests that the rate of de novo purine biosynthesis in this erythroleukemic cell line is not limited by the availability of phosphoribosylpyrophosphate, but rather by a decrease in the phosphoribosyl‐l‐amine synthesizing enzymes. These findings provide further evidence that during dimethyl‐sulfoxide‐stimulated erythroid maturation, the same regulatory mechanisms are operative as in normal cellular development, and that ammonia‐dependent purine biosynthesis is subject to the same regulatory mechanisms as is glutamine‐dependent biosynthesis.