title: Elucidation of aberrant purine metabolism: application to hypoxanthine-guanine phosphoribosylstransferase- and adenosine kinase-deficient mutants, and IMP dehydrogenase- and adenosine deaminase-inhibited human lymphoblasts.
abstract: We propose that the ratio of [14C]formate-labelled purine nucleosides and bases (both intra and extracellular) to nucleic acid purines provides, in exponentially growing cultures, a sensitive index for comparative studies of purine metabolism. This ratio was 4-fold greater for an HGPRT- mutant than for the parental HGPRT+ human lymphoblast line. The major components of the labelled nucleoside and base fraction were hypoxanthine and inosine. By blocking adenosine deaminase activity with coformycin we found that approx. 90% of inosine was formed directly from IMP rather than the route IMP leads to AMP leads to adenosine leads to inosine. The ratio of labelled base + nucleosides to nucleic acids was essentially unchagned for an AK- lymphoblast line and 2-fold greater than control for an HGPRT(-)-KAK- line, demonstrating that a deficiency of adenosine kinase alone has little effect on the accumulation of purine nucleosides and bases. Although adenosine was a minor component of the nucleoside and base fraction, the adenosine fraction increased from 3 to 13% with the addition of coformycin to the HGPRT(-)-AK- line. In the parental and HGPRT- lines, adenosine was shown to be primarily phosphorylated rather than deaminated at concentrations less than 5 microM. Inhibition of IMP dehydrogenase activity by mycophenolic acid caused a 12- and 3-fold increase in the rate of production of labelled base and nucleoside in the parent and HGPRT- cells respectively. These results suggest that a mutationally induced partial deficiency in the activities converting IMP to guanine nucleotides may result in an increased catabolism of IMP.
mesh_terms: D058892:Adenosine Deaminase Inhibitors; D000248:Adenosine Kinase / Q000172:deficiency* / Q000235:genetics; D002478:Cells, Cultured; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000172:deficiency* / Q000235:genetics; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors*; D007658:Ketone Oxidoreductases / Q000037:antagonists & inhibitors*; D008214:Lymphocytes / Q000378:metabolism*; D009154:Mutation; D009700:Nucleoside Deaminases / Q000037:antagonists & inhibitors*; D010770:Phosphotransferases / Q000172:deficiency*; D011684:Purine Nucleosides / Q000096:biosynthesis; D011687:Purines / Q000378:metabolism*
chemical_list: D058892:Adenosine Deaminase Inhibitors; D011684:Purine Nucleosides; D011687:Purines; D007168:IMP Dehydrogenase; D007658:Ketone Oxidoreductases; D007041:Hypoxanthine Phosphoribosyltransferase; D010770:Phosphotransferases; D000248:Adenosine Kinase; D009700:Nucleoside Deaminases