Variation of phosphoribosylpyrophosphate synthetase activity in human cells

Abstract

AbstractThe behavior of phosphoribosylpyrophosphate (PRPP) synthetase during the cell cycle was studied using RSa cells derived from human fetal fibroblasts. The cells were synchronized by the double thymidine block method. PRPP synthetase activity in cell extracts increased 2‐fold in the S phase. Metabolic flux through phosphoribosylpyrophosphate into nucleotides, which represents the in situ activity of PRPP synthetase, increased 3‐fold in the S phase. The mRNA levels of PRPP synthetase subunit I and II genes (PRPS1 and PRPS2 respectively) increased 3‐fold and the increase preceded elevation of enzyme activity in the S phase. Thus variation in PRPP synthetase activity during the cell cycle is ascribed mainly to varying amounts of the enzyme. Degradation of PRPS1 and PRPS2 mRNA was significantly suppressed in the early S phase and was presumably related to periodic accumulation of the two mRNAs. In earlier work, it was found that the expression of PRPP synthetase isoform genes PRPS1 and PRPS2 is regulated in a tissue specific manner, thereby suggesting a functional difference between them. We have now obtained evidence that there is no apparent difference between the expression of PRPS1 and PRPS2 genes in the cell cycle.