Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
 2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

De novo purine biosynthesis has been studied in lymphocyte cell lines established from Lesch-Nyhan patients deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRT), in in vitro differentiating erythroleukaemic cell lines cloned from cells charactistic of virus-induced murine leukaemia, and in mutant hamster cells deficient in amidophosphoribosyltransferase. The relationship between cellular phosphoribosylpyrophosphate (PP-ribose-P) metabolism and the activity of the enzymes which catalyse the early steps of de novo purine biosynthesis has been explored. It was found that hamster cells deficient in amidophosphoribosyltransferase did not accumulate PP-ribose-P as do HGPRT-deficient cells. In these model systems, an accelerated rate of de novo purine biosynthesis tended to be associated with an increase in cellular PP-ribose-P cotent, but decreases in this rate results from the reduction in the activity of amidophosphoribosyltransferase. Regulation of ammonia-dependent de novo purine biosynthesis was similar to that of glutamine-dependent purine biosynthesis.
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PMID:Purine biosynthesis in mutant mammalian cells. 20 59

Human B lymphoblast lines severely deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRT) were selected for resistance to 6-thioguanine from cloned normal and phosphoribosylpyrophosphate (PP-Rib-P) synthetase-superactive cell lines and were compared with their respective parental cell lines with regard to growth and PP-Rib-P and purine nucleotide metabolism. During blockade of purine synthesis de novo with 6-methylthioinosine or aminopterin, inhibition of growth of all HGPRT-deficient cell lines was refractory to addition of Ade at concentrations which restored substantial growth to parental cell lines. Ade-resistant inhibition of growth of parental lines by 6-methylthioinosine, however, occurred during Ado deaminase inhibition. Insufficient generation of IMP (and ultimately guanylates) to support growth of lymphoblasts lacking HGPRT activity and blocked in purine synthesis de novo best explained these findings, implying that a major route of interconversion of AMP to IMP involves the reaction sequence: AMP----Ado----Ino----Hyp----IMP. PP-Rib-P generation and purine nucleoside triphosphate pools were unchanged by introduction of HGPRT deficiency into normal lymphoblast lines, in agreement with the view that accelerated purine synthesis de novo in this deficiency results from increased availability of PP-Rib-P for the pathway. Cell lines with dual enzyme defects did not differ from PP-Rib-P synthetase-superactive parental lines in rates of PP-Rib-P and purine synthesis despite 5-6-fold increases in PP-Rib-P concentrations, excretion of nearly 50% of newly synthesized purines, and diminished GTP concentrations. Fixed rates of purine synthesis de novo in PP-Rib-P synthetase-superactive cells appeared to reflect saturation of the rate-limiting amidophosphoribosyltransferase reaction for PP-Rib-P. In combination with accelerated purine excretion, increased channeling of newly formed purines into adenylates, and impaired conversion of AMP to IMP, fixed rates of purine synthesis de novo may condition cell lines with defects in HGPRT and PP-Rib-P synthetase to depletion of GTP with consequent growth retardation.
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PMID:Regulation of purine nucleotide synthesis in human B lymphoblasts with both hypoxanthine-guanine phosphoribosyltransferase deficiency and phosphoribosylpyrophosphate synthetase superactivity. 131 6

The proliferative effect of insulin on de novo purine synthesis and on the expression of various enzymes of purine metabolism were studied in primary cultured rat hepatocytes. Insulin greater than 1.5 x 10(-8) M increased DNA and de novo purine synthesis to 260-390 and 270-420%, respectively, 24 and 8 h after the administration. Insulin at 1.5 x 10(-7) M increased the specific activity of amidophosphoribosyltransferase (ATase) to 154-180%, hypoxanthine-guanine phosphoribosyltransferase to 129%, and adenine phosphoribosyltransferase (APRT) to 205%, in contrast to unchanged xanthine dehydrogenase at 80%. Enzyme induction was supported by the results of kinetic analysis and the inhibition of the insulin-induced increase in enzyme activities by protein synthesis inhibitors. Insulin increased ATP to 127% and decreased AMP, ADP, 5'-guanylic acid (GMP), and guanosine 5'-diphosphate (GDP), respectively, to 73, 69, 73, and 69%. Insulin increased adenylate energy charge from 0.83 to 0.90 without changing total feedback inhibitory potential on ATase. No obvious increase of 5-phosphoribosyl-1-pyrophosphate supply was suggested, although its apparent availability for purine ribonucleotide synthesis was increased to 208-245%, reflecting mainly induced APRT activity to 205%. It is concluded that hepatocyte proliferation by insulin, as evidenced by purine metabolism, is mediated by the selective gene activation of anabolic enzymes and increased ATP as the basis to activate multiple metabolic pathways without remarkable changes of substrate availability or feedback inhibition.
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PMID:Increased de novo purine synthesis by insulin through selective enzyme induction in primary cultured rat hepatocytes. 218 59

Previous studies of purine nucleotide synthesis de novo have suggested that major regulation of the rate of the pathway is affected at either the phosphoribosylpyrophosphate (PP-Rib-P) synthetase reaction or the amidophosphoribosyltransferase (amido PRT) reaction, or both. We studied control of purine synthesis de novo in cultured normal, hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-deficient, and PP-Rib-P synthetase-superactive human fibroblasts by measuring concentrations and rates of synthesis of PP-Rib-P and purine nucleotide end products, proposed effectors of regulation, during inhibition of the pathway. Incubation of cells for 90 min with 0.1 mM azaserine, a glutamine antagonist which specifically blocked the pathway at the level of conversion of formylglycinamide ribotide, resulted in a 5-16% decrease in purine nucleoside triphosphate concentrations but no consistent alteration in generation of PP-Rib-P. During this treatment, however, rates of the early steps of the pathway were increased slightly (9-15%) in normal and HGPRT-deficient strains, more markedly (32-60%) in cells with catalytically superactive PP-Rib-P synthetases, and not at all in fibroblasts with purine nucleotide feedback-resistant PP-Rib-P synthetases. In contrast, glutamine deprivation, which inhibited the pathway at the amido PRT reaction, resulted in time-dependent nucleoside triphosphate pool depletion (26-43% decrease at 24 h) accompanied by increased rates of PP-Rib-P generation and, upon readdition of glutamine, substantial increments in rates of purine synthesis de novo. Enhanced PP-Rib-P generation during glutamine deprivation was greatest in cells with regulatory defects in PP-Rib-P synthetase (2-fold), but purine synthesis in these cells was stimulated only 1.4-fold control rates by glutamine readdition. Stimulation of these processes in normal and HGPRT-deficient cells and in cells with PP-Rib-P synthetase catalytic defects was, respectively: 1.5 and 2.0-fold; 1.5 and 1.7-fold; and 1.6 and 4.1-fold. These studies support the following concepts. 1) Rates of purine synthesis de novo are regulated at both the PP-Rib-P synthetase and amido PRT reactions by end products, with the latter reaction more sensitive to small changes in purine nucleotide inhibitor concentrations. 2) PP-Rib-P exerts its role as a major regulator of purine synthetic rate by virtue of its interaction with nucleotide inhibitors to determine the activity of amido PRT. 3) Activation of amido PRT by PP-Rib-P is nearly maximal at base line in fibroblasts with regulatory defects in PP-Rib-P synthetase.
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PMID:Regulation of purine synthesis de novo in human fibroblasts by purine nucleotides and phosphoribosylpyrophosphate. 244 88

An improved method was developed to align related protein sequences and search for homology. A glutamine amide transfer domain was identified in an NH2-terminal segment of GMP synthetase from Escherichia coli. Amino acid residues 1-198 in GMP synthetase are homologous with the glutamine amide transfer domain in trpG X D-encoded anthranilate synthase component II-anthranilate phosphoribosyltransferase and the related pabA-encoded p-aminobenzoate synthase component II. This result supports a model for gene fusion in which a trpG-related glutamine amide transfer domain was recruited to augment the function of a primitive NH3-dependent GMP synthetase. Sequence analyses emphasize that glutamine amide transfer domains are thus far found only at the NH2 terminus of fused proteins. Two rules are formulated to explain trpG and trpG-related fusions. (i) trpG and trpG-related genes must have translocated immediately up-stream of genes destined for fusion in order to position a glutamine amide transfer domain at the NH2 terminus after fusion. (ii) trpG and trpG-related genes could not translocate adjacent to a regulatory region at the 5' end of an operon. These rules explain known trpG-like fusions and explain why trpG and pabA are not fused to trpE and pabB, respectively. Alignment searches of GMP synthetase with two other enzymes that bind GMP, E. coli amidophosphoribosyltransferase and human hypoxanthine-guanine phosphoribosyltransferase, suggest a structurally homologous segment which may constitute a GMP binding site.
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PMID:Identification of a trpG-related glutamine amide transfer domain in Escherichia coli GMP synthetase. 298 57

The regulation and integration of purine nucleotide biosynthesis is considered from the viewpoint of the main groups of reaction sequences involved and with respect to some specific organs and tissues. Inhibiting either IMP dehydrogenase or adenylosuccinate synthetase in rat liver in vitro reduced the rate of purine do novo synthesis with respect to the purine remaining in the tissue and did not materially affect the rate with respect to the purines extruded into the incubation medium. These results are considered in contrast to the results of previous studies in cultured lymphoblasts. The relative activities of purine de novo synthesis and of purine salvage have been assessed in different tissues by the activities of amidophosphoribosyltransferase and hypoxanthine phosphoribosyltransferase (HPRT), respectively. Changes in purine de novo synthesis as measured by [14C]formate incorporation into cellular purines were reflected in the amidophosphoribosyltransferase activities. The capacity of different tissues to synthesize purines de novo is widespread and the role of the liver as the main site of purine de novo synthesis in vivo and exporting purines to other tissues appears questionable. Regulatory mechanisms may well be tissue specific. The age-related changes in the activity of the purine de novo synthesis and purine salvage pathways, respectively, in the brain suggest that it is physiological or neuropharmacological functions of the developed brain rather than cell division and organogenesis which require a high level of purine salvage relative to purine de novo synthesis. This is compatible with the observation that purine de novo synthesis alone can meet the needs for additional purine nucleotides which lectin induced lymphocyte transformation involves. The mechanism whereby purine de novo synthesis is initiated during lectin induced lymphoblast transformation remains obscure.
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PMID:Some regulatory and integrative aspects of purine nucleotide biosynthesis and its control: an overview. 615 30

(1) This communication reports the amidophosphoribosyltransferase (PRPP-At; EC2.4.2.14), hypoxanthine phosphoribosyltransferase (HPRT; EC2.4.2.7) and adenine phosphoribosyltransferase (APRT; EC2.4.2.8) activities and the phosphoribosylpyrophosphate (PRPP) content of rat brain at different stages of development. The results are not age-related in the foetal and neonatal animals and the data for whole brain homogenates are similar to the average results for the individual regions of the brain at the same stage of development. (2) The enzyme activities and PRPP content are similar in the different regions of the rat central nervous system. PRPP-At has the lowest activity of the 3 enzymes studied and this decreases gradually from birth until 8 weeks. HPRT is the most active of the three enzymes, its activity increases markedly between birth and the end of the third week of life. The time course of these changes shows only minor differences between the regions of the brain studied. The ratio of HPRT activity to PRPP-At activity increases from age 1 week in all parts of the rat brain. (3) The APRT activities in rat brain are intermediate between those of PRPP-At and HPRT and essentially steady except for a decrease in the cerebellum during the first 3 weeks of life. (4) The PRPP concentrations in rat brain decrease between birth and the end of the 3rd week of life. (5) The systemic tissues examined have PRPP-At, HPRT and APRT activities. The relationship between the activities of the different enzymes appears to be characteristic of the tissue concerned. (6) Correlating the observed time course of the changes in the ratio of hypoxanthine phosphoribosyltransferase activity to amidophosphoribosyltransferase activity in the rat with other workers' data on changes in the rate of DNA accretion in human brain during development indicates that the main increase in this ratio is after the major bursts of neuroblast and neuroglia proliferation. We suggest that the neurological dysfunction in the Lesch-Nyhan syndrome is due to lack of a purine derivative with a physiological or neuropharmacological function, rather than to an effect of the biochemical lesion on brain morphogenesis.
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PMID:Activities of amidophosphoribosyltransferase (EC2.4.2.14) and the purine phosphoribosyltransferases (EC2.4.2.7 and 2.4.2.8), and the phosphoribosylpyrophosphate content of rat central nervous system at different stages of development--their possible relationship to the neurological dysfunction in the Lesch-Nyhan syndrome. 615 47

The enzymic capacities of the de novo and the salvage pathways for purine nucleotide synthesis were compared in rat in normal, differentiating, and regenerating liver, and in three hepatomas of widely different growth rates. The activities of the key de novo and salvage enzymes were also determined in mouse lung and Lewis lung carcinoma, in human kidney and liver, and in renal cell carcinoma and hepatocellular carcinomas. A precise and reproducible assay was worked out for measuring the activities of adenine phosphoribosyltransferase (EC 2.4.2.7) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8) in crude liver and hepatoma systems. Kinetic studies on the salvage enzymes were carried out in the crude 100,000 X g supernatant fluid from normal liver and rapidly growing hepatoma 3924A. In both tissue extracts, Michaelis-Menten kinetics was observed for adenine phosphoribosyltransferase and HGPRT. The reciprocal plots for 5-phosphoribosyl-1-pyrophosphate (PRPP) of liver and hepatoma enzymes gave apparent KmS of 2 microM for adenine phosphoribosyltransferase and 4 microM for HGPRT, showing two orders of magnitude higher affinities for PRPP than that of the rate-limiting enzyme of de novo purine synthesis, amidophosphoribosyltransferase (EC 2.4.2.14) (Km = 400 to 900 microM). The apparent Km values for adenine of liver and hepatoma adenine phosphoribosyltransferase were 0.6 to 0.9 microM, respectively. For both liver and hepatoma HGPRT, the reciprocal plots for hypoxanthine and guanine yielded the same Km of 3 microM. The specific activities of purine phosphoribosyltransferases were markedly higher than that of amidophosphoribosyltransferase in rat thymus, spleen, testis, bone marrow, colon, liver, kidney cortex, lung, heart, brain, and skeletal muscle, but were lower in the small intestine. In hepatomas and regenerating and differentiating liver, the activities of the salvage enzymes were 2.1- to 32-fold higher than that of amidophosphoribosyltransferase. The purine phosphoribosyltransferase activities were also higher than that of amidophosphoribosyltransferase in Lewis lung carcinoma (8.2- to 32-fold), human renal cell carcinoma (3.5- to 22-fold), and hepatocellular carcinoma (3.4- to 30-fold). The high activities and the high affinity to PRPP of the purine phosphoribosyltransferases might explain the lack of linkage of the behavior of these enzymic activities with proliferation in normal, regenerating, differentiating, or neoplastic tissues. In contrast, the specific activity of the amidophosphoribosyltransferase, which is lower than that of the salvage enzymes, is linked with transformation as it is increased in all examined tumors.4
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PMID:Enzymic capacities of purine de Novo and salvage pathways for nucleotide synthesis in normal and neoplastic tissues. 632 16

Yeast mutants lacking activity of the enzyme hypoxanthine:guanine phosphoribosyltransferase (H:G-PRT) have been isolated by selecting for resistance to 8-azaguanine in a strain carrying the wild type allele, ade4%, of the gene coding for amidophosphoribosyltransferase (PRPPAT), the first enzyme of de novo purine synthesis. The mutants excrete purines and are cross-resistant to 8-azaadenine. They are recessive and represent a single complementation group, designated hpt1. Ade4-su, a prototrophic allele of ade4 with reduced activity of PRPPAT, is epistatic to hpt1, suppressing purine excretion and resistance to azaadenine but not resistance to azaguanine. The genotype ade2hpt1 does not respond to hypoxanthine. Hpt1 complements and is not closely linked to the purine excreting mutants pur1 to pur5. Hpt1 and pur6, a regultory mutant of PRPPAT, are also unlinked but do not complement, suggesting a protein-protein interaction between H:G-PRT and PRPPAT. Mycophenolic acid (MPA), an inhibitor of de novo guanine nucleotide synthesis, inhibits the growth of hpt1 and hpt1+. Xanthine allows both genotypes to grow in the presence of MPA whereas guanine only allows growth of hpt1+. Activity of A-PRT, X-PRT and H:G-PRT is present in hpt+. Hpt1 lacks activity of H:G-PRT but has normal A-PRT and X-PRT.
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PMID:Hypoxanthine: guanine phosphoribosyltransferase mutants in Saccharomyces cerevisiae. 635 64

Mutants of Saccharomyces cerevisiae deficient in adenine phosphoribosyltransferase (A-PRT, EC 2,4,2,7) have been isolated following selection for resistance to 8-azaadenine in a prototrophic strain carrying the ade4-su allele of the gene coding for amidophosphoribosyltransferase (EC 2,4,2,14). The mutants were recessive and defined a single gene, apt1. They did not excrete purine when combined with ade4+. The mutants appeared to retain some A-PRT activity in crude extracts, and strains of the genotype ade2 apt1 responded to both adenine and hypoxanthine. Mutants deficient in adenine aminohydrolase (EC 3,5,4,2) activity, aah1, and hypoxanthine:guanine phosphoribosyltransferase (EC 2,4,2,8) activity, hpt1, were used to synthesize the genotypes apt1 hpt1 aah+ and apt1 hpt+ aah1. The absence of A-PRT activity in strains with these genotypes confirmed the hypothesis that the residual A-PRT activity of apt1 mutants was due to adenine aminohydrolase and hypoxanthine:guanine phosphoribosyltransferase acting in concert.
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PMID:Adenine phosphoribosyltransferase mutants in Saccharomyces cerevisiae. 639 74


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