Alterations in several specific
enzymes have been associated with increased rates of
purine synthesis de novo in human and other mammalian cells. However, these recognized abnormalities in humans account for only a few percent of the clinical cases of
hyperuricemia and
gout. We have examined in detail the rates of
purine production de novo and
purine excretion by normal and by mutant (AU-100) murine
lymphoma T cells (S49) 80% deficient in
adenylosuccinate synthetase [
IMP:L-aspartate ligase (GDP-forming), EC 6.3.4.4]. The intracellular
ATP concentration of the mutant cells is slightly diminished, but their
GTP is increased 50% and their
IMP, four-fold. Compared to wild-type cells, the AU-100 cells excrete into the culture medium 30- to 50-fold greater amounts of
purine metabolites consisting mainly of
inosine. Moreover, the AU-100 cell line overproduces total
purines. In an AU-100-derived cell line, AU-TG50B, deficient in
adenylosuccinate synthetase and
hypoxanthine/guanine phosphoribosyltransferase (
IMP:
pyrophosphate phosphoribosyltransferase, EC 2.4.2.8),
purine nucleoside excretion is increased 50- to 100-fold, and de novo synthesis is even greater than that for AU-100 cells. The overexcretion of
purine metabolites by the AU-100 cells seems to be due to the primary genetic deficiency of
adenylosuccinate synthetase, a deficiency that requires the cell to increase intracellular
IMP in an attempt to maintain
ATP levels. As a consequence of elevated
IMP pools, large amounts of
inosine are secreted into the culture medium. We propose that a similar primary genetic defect may account for the excessive
purine excretion in some patients with dominantly inherited
hyperuricemia and
gout.