title: Mechanisms of accelerated purine nucleotide synthesis in human fibroblasts with superactive phosphoribosylpyrophosphate synthetases.
abstract: Concentrations and rates of synthesis of phosphoribosylpyrophosphate (PP-Rib-P) and purine nucleotides were compared in fibroblasts cultured from 5 males with PP-Rib-P synthetase superactivity, 3 normal individuals, and 2 children with severe hypoxanthine-guanine phosphoribosyltransferase deficiency. Although all cell strains with PP-Rib-P synthetase superactivity showed increased PP-Rib-P concentration and generation, increased rates of PP-Rib-P-dependent purine synthetic pathways, and increased purine and pyrimidine nucleoside triphosphate concentrations, two subgroups were discernible. Three fibroblast strains with isolated catalytic defects in PP-Rib-P synthetase showed milder increases in PP-Rib-P concentration (2.5-fold normal) and generation (1.6- to 2.1-fold) and in rates of purine synthesis de novo (1.6- to 2.2-fold) and purine nucleoside triphosphate pools (1.5-fold) than did cells from 2 individuals with combined kinetic defects in PP-Rib-P synthetase, both with purine nucleotide inhibitor-resistance. Values for these processes in the latter two strains were, respectively, 5- to 6-fold, 2.6- to 3.2-fold, 4- to 7-fold, and 1.7- to 2.2-fold those of normal cells. In contrast to cells with catalytic defects, these cells also excreted an abnormally high proportion of labeled purines and resisted purine base-mediated inhibition of PP-Rib-P and purine nucleotide synthesis. Hypoxanthine-guanine phosphoribosyltransferase-deficient cells showed normal regulation of PP-Rib-P synthesis and normal nucleoside triphosphate pools despite increased rates of purine synthesis de novo and of purine excretion. Cells with PP-Rib-P synthetase superactivity thus synthesize purine nucleotides at increased rates as a consequence of increased PP-Rib-P production, despite increased purine nucleotide concentrations. These and additional findings provide evidence that regulation of purine synthesis de novo is effected at both the PP-Rib-P synthetase and amidophosphoribosyltransferase reactions.
mesh_terms: D001706:Biopsy; D002478:Cells, Cultured; D002648:Child; D005347:Fibroblasts / Q000201:enzymology; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000172:deficiency; D007700:Kinetics; D007926:Lesch-Nyhan Syndrome / Q000201:enzymology; D008297:Male; D010770:Phosphotransferases / Q000378:metabolism*; D011685:Purine Nucleotides / Q000096:biosynthesis*; D012016:Reference Values; D012268:Ribose-Phosphate Pyrophosphokinase / Q000378:metabolism*; D012867:Skin / Q000201:enzymology*
chemical_list: D011685:Purine Nucleotides; D007041:Hypoxanthine Phosphoribosyltransferase; D010770:Phosphotransferases; D012268:Ribose-Phosphate Pyrophosphokinase