Folate‐deficient human lymphoblasts: changes in de novo purine and pyrimidine synthesis and phosphoribosylpyrophosphate

Peripheral blood lymphocytes from healthy volunteers cultured with phytohaemagglutinin in a folate-deficient medium exhibit megaloblastic maturation and reduced cellular folate content. For these cells, changes in de novo purine and pyrimidine synthesis and cellular phosphoribosylpyrophosphate (PRPP) have been determined. Mitogen-stimulated cells cultured with undialyzed pooled human serum (PHS) exhibit undetectable de novo purine synthesis, a three-fold increase in PRPP content and augmented de novo pyrimidine synthesis; these changes are independent of cellular folate status. Folate-replete cells cultured with PHS which was dialyzed to reduce purine compounds concentrations show markedly increased de novo purine synthesis. The PRPP content and pyrimidine synthesis rates of these cells are similar to those of folate-replete cells cultured with undialyzed PHS. Folate-deficient cells cultured in dialyzed PHS show a 10-fold reduction in purine synthesis and a corresponding increase in PRPP levels. Pyrimidine synthesis was moderately reduced. The purine bases hypoxanthine and adenine markedly reduced the augmented purine synthesis of folate-replete cells or the increased PRPP content of folate-deficient cells cultured with dialyzed PHS. These findings suggest that cellular folate status is critical for de novo purine synthesis only when coupled with purine bases restriction and that the latter are efficient regulators of de novo purine synthesis.