Factors affecting the rate of purine ribonucleotide dephosphorylation in human erythrocytes.

Purine ribonucleotide dephosphorylation was measured in intact human erythrocytes in vitro to evaluate those factors which might regulate this process in vivo. It was found that purine nucleotides which exist predominantly in the triphosphate form (e.g. ATP and GTP) are protected from dephosphorylation while those nucleotides normally present as the monophosphate (e.g. IMP) are susceptible to dephosphorylation. This point was emphasised by studying an individual whose erythrocytes accumulated ITP rather than IMP; erythrocytes from this individual has a more stable pool of inosine phosphates than did erythrocytes from normal individuals. The concentration of intracellular phosphate was also shown to affect the rate of dephosphorylation. The dephosphorylation of IMP was inhibited at intracellular phosphate concentrations above approx. 3 mM. AMP dephosphorylation (in cells whose AMP concentration was increased by incubating them in the presence of 2-deoxyglucose) was inhibited by phosphate more strongly than was found for IMP. In contrast, the dephosphorylation of GMP did not appear to be affected by phosphate concentration. High oxygen tension was a powerful stimulator of IMP dephosphorylation while low oxygen tension protected IMP from dephosphorylation. This finding shows that human erythrocytes are similar to those of other mammals in this regard and points to a possible physiological determinant of purine turnover in these cells.