Inosine/pyruvate/phosphate medium but not adenosine/pyruvate/phosphate medium introduces millimolar amounts of 5-phosphoribosyl 1-pyrophosphate in human erythrocytes. A 31P-n.m.r. study.

Incubation of human erythrocytes in medium containing inosine (10 mM), pyruvate (10 mM), phosphate (50 mM) and NaCl (75 mM) at pH 6.6 leads to a more than 1000-fold increase in the concentration of 5-phosphoribosyl 1-pyrophosphate (PRPP), as identified and quantified by 31P-n.m.r. spectroscopy. The accumulation is highly pH-dependent, with a maximum at extracellular pH 6.60, and the maximum value of 1.3-1.6 mmol/l of erythrocytes is attained within 1 h at 37 degrees C. PRPP was accumulated despite high concentrations of 2,3-bisphosphoglycerate (2,3-BPG), an inhibitor of PRPP synthetase. The concentration of PRPP correlated with the intracellular concentration of inorganic phosphate (Pi). Substitution of either adenosine or adenosine plus inosine for inosine in the medium did not lead to 31P-n.m.r.-detectable accumulation of PRPP. These results show that neither 2,3-BPG nor PRPP itself inhibits the synthesis of PRPP in the human erythrocyte. Adenosine, however, prevents the inosine-stimulated accumulation of PRPP.