The intracellular
ribose 5-phosphate concentration was found to be an important determinant of rates of de novo
purine synthesis. When
ribose 5-phosphate production was reduced in cultured human lymphoblasts by
glucose starvation, the intracellular phosphoribosylpyrophosphate concentration and rates of de novo
purine synthesis decreased. Inosinate-guanylate:
pyrophosphate phosphoribosyltransferase (HPR
transferase)-deficient cells were relatively more resistant to
glucose starvation. To minimize the effect of
purine nucleotide feedback inhibition on the de novo pathway, cells were treated with inhibitors of
IMP dehydrogenase and
adenylosuccinate synthetase. In normal lymphoblasts,
purine synthesis was stimulated only at
glucose concentrations greater than 100 microM while in HPR
transferase-deficient lymphoblasts, stimulation occurred even in the absence of
glucose. The differences between the normal and HPR
transferase-deficient cells were lost when
ribose reutilization from endogenous
nucleotide breakdown was impaired in the HPR
transferase-deficient cells by incubation with
2'-deoxyinosine. Endogenous
ribose reutilization for
purine synthesis is, therefore, important when either
glucose availability is limited or synthesis is stimulated. In the absence of
glucose, exogenous
purine nucleotides restored the intracellular concentrations of
ribose 5-phosphate, phosphoribosylpyrophosphate, and
purine nucleotides to almost 100% and rates of
purine synthesis to 50-75% of those
at 10 mM
glucose. When
ribose 5-phosphate production was increased in peripheral blood lymphocytes by
phytohemagglutinin activation, the intracellular phosphoribosylpyrophosphate concentration and rates of de novo
purine synthesis increased.