Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00492 (hypoxanthine-guanine phosphoribosyltransferase)
2,385 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

2-Amino-6-chloro-1-deazapurine is of interest as a purine analog with demonstrated in vivo activity against mouse leukemia L1210. That the active form of this agent is a nucleotide and that the nucleotide is formed by the action of hypoxanthine (guanine) phosphoribosyltransferase were shown by the facts that (a) L1210 cells deficient in hypoxanthine phosphoribosyltransferase were insensitive to the analog; (b) hypoxanthine, but not adenine, prevented the formation of the analog nucleotide by enzyme preparations containing activities of both hypoxanthine and adenine phosphoribosyltransferases; and (c) the cytotoxicity of the analog was prevented by hypoxanthine. The ribonucleoside of this analog was not toxic to cell cultures and hence is not phosphorylated or cleaved to the base. In intact HEp-2 cells and L1210 cells, the analog was metabolized to the nucleoside 5'-phosphate which accumulated to concentrations as high as 1000 nmoles/10(9) cells; no di- or triphosphates were detected. In HEp-2 cells, the analog reduced the pools of purine nucleotides with some accumulation of IMP. The toxicity of minimal inhibitory concentrations of the analog to HEp-2 cells could be prevented or reversed by 4(5)-amino-5(4)-imidazolecarboxamide (AIC); the toxicity of higher concentrations could be prevented or reversed by a combination of adenine and guanosine but not by AIC. The analog inhibited the incorporation of formate into purine nucleotides and into macromolecules at concentrations that had no effect on utilization of hypoxanthine; at higher concentrations the incorporation of hypoxanthine was inhibited. Low concentrations also inhibited the utilization of uridine and thymidine. The incorporation of hypoxanthine and AIC into guanine nucleotides, but not adenine nucleotides, was inhibited. These results indicate two sites of inhibition of the biosynthesis of purine nucleotides, the more sensitive one being on an early step of the pathway and the less sensitive one on the IMP-GMP conversion. That the blockade of de novo synthesis probably was at the site of feedback inhibition was indicated by the fact that the analog inhibited the accumulation of formylglycinamide ribonucleotide in azaserine-treated cells but did not inhibit the synthesis of 5'-phosphoribosyl 1-pyrophosphate. Comparative studies were performed with the related analog, 2-amino-6-chloropurine, which has been reported to produce a similar dual blockade of the purine pathway. This purine was less toxic than its 1-deaza analog; it produced a modest decrease in adenine nucleotides but increased pools of guanine nucleotides.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mode of action of 2-amino-6-chloro-1-deazapurine. 614 12

The 1-phosphorothioate analogues of 5-phosphoribosyl 1-diphosphate (P-Rib-PP) have been prepared enzymatically, in reactions catalyzed by P-Rib-PP synthetase from Salmonella typhimurium. 5-Phosphoribosyl 1-O-(2-thiodiphosphate) (P-Rib-PP beta S) was synthesized from ribose 5-phosphate (Rib-5-P) and the Mg2+ complex of adenosine 5'-O-(3-thiotriphosphate). The SP and RP diastereomers of 5-phosphoribosyl 1-O-(1-thiodiphosphate) (P-Rib-PP alpha S) were synthesized from Rib-5-P and the Mg2+ complex of adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) (SP diastereomer, delta-configuration) and the Cd2+ complex of ATP beta S (RP diastereomer, delta-configuration), respectively. The strategy for the synthesis and stereochemical assignment of the P-Rib-PP alpha S diastereomers was based on the specificity of P-Rib-PP synthetase for the (delta)-beta, gamma-bidentate metal-nucleotide substrate and the stereochemical course of the synthetase reaction, leading to inversion of configuration at the P beta atom of the nucleotide [Li, T. M., Mildvan, A. S., & Switzer, R. L. (1978) J. Biol. Chem. 253, 3918-3923], and the known configurations of the Mg2+ and Cd2+ beta, gamma-bidentate complexes of the ATP beta S diastereomers [Jaffe, E. K., & Cohn, M. (1979) J. Biol. Chem. 254, 10839-10845]. The P-Rib-PP analogues were purified by gradient elution from DEAE-Sephadex and characterized by chemical analysis and 31P nuclear magnetic resonance [Smithers, G. W., & O'Sullivan, W. J. (1984) Biochemistry (following paper in this issue)]. A preliminary account of their interaction with human brain hypoxanthine phosphoribosyltransferase and yeast orotate phosphoribosyltransferase (OPRTase) is described.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phosphorothioate analogues of 5-phosphoribosyl 1-diphosphate: synthesis, purification, and partial characterization. 620 37

The frequency of phenotypic expression of the herpes simplex virus type 1 tk and Escherichia coli gpt genes was compared with the frequency of genotypic transformation after calcium phosphate-mediated DNA transfection of a number of tk- and hprt- cell lines. In three of the five lines tested, the frequency of phenotypic expression was at most 10-fold higher than that of genotypic transformation as indicated by frequency of HAT resistance. The remaining two lines showed phenotypic responses which were 50- to 100-fold greater than the genotypic responses. The data indicate that the efficiency of DNA-mediated transformation with some cell lines can be limited by events after the uptake and expression of transfected DNA.
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PMID:Comparison of phenotypic expression with genotypic transformation by using cloned, selectable markers. 628 41

Sealed and unsealed plasma membrane vesicles were prepared from human erythrocytes and lymphocytes. Phosphoribosylpyrophosphate synthetase (PRibPP synthetase), hypoxanthine phosphoribosyltransferase (HPRTase), and adenine phosphoribosyltransferase (APRTase) activities are detectable on both inside-out and right-side-out sealed vesicles. Ghost preparations were about 0.2%, 1%, and 1.2% of the total erythrocyte and 0.5%, 5.3%, and 9.7% of the lymphocyte APRTase, HPRTase, and PRibPP synthetase activities. The rapid decrease in these enzyme activities, upon further purification of the membranes, seemed to suggest that they might be loosely bound extrinsic proteins. Evidence confirming the localization of these enzymes on the cell surface was obtained by measuring production of [14C]AMP by intact cells in medium containing [14C]adenine, ribose 5-phosphate, and Mg2+ATP. The formation of AMP was linear with time and number of cells present. Magnesium and phosphate exerted different effects on the production of extracellular AMP than on intracellular, which involves transport as well as phosphoribosylation. Cytosoluble and membrane-bound APRTase and PRibPP synthetase exhibited different catalytic properties and sensitivities to effectors. Membranes of erythrocytes of HPRTase-deficient patients contain little or no HPRTase activity when assayed in the absence of Triton. Reisolation of these membranes from admixture with normal hemolysates did not result in any bound activity; thus, the membrane-bound activity is not an artifact of the isolation procedure. Lysis with Triton released activity equal to about half that of control membranes. This is further evidence that the enzyme is firmly bound to the membrane.
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PMID:Membrane-associated purine metabolizing enzyme activities of human peripheral blood cells. 629 41

The use of high-performance liquid chromatography to identify and quantitate five purine-metabolizing enzymes from a partially purified subcellular fraction of the eucaryotic microorganism Dictyostelium discoideum is described. All HPLC separations were carried out in an isocratic manner using reverse-phase C18 as the stationary phase. The mobile phase consisted of a phosphate buffer with either methanol or acetonitrile as cosolvent, and optimal separation conditions were attained by varying the organic concentration or the pH of the buffer or by employing paired-ion chromatographic techniques. Substrates and products were detected at either 254 nm for the purines or 295 nm for the formycin analogs. An adenosine kinase activity was identified, and it was demonstrated that formycin A (FoA) could be substituted for adenosine as the phosphate acceptor, yielding FoAMP as the product. With FoA as the substrate an apparent Km of 18.2 microM and an apparent Vmax of 32.4 mmol min-1 mg-1 were observed for the activity. A purine-nucleoside phosphorylase activity was found to cleave adenosine to adenine and ribosylphosphate. FoA was not found to be a substrate for this activity due to the unusual formycin C-glycosyl bond which was not hydrolyzed by enzymes or chemically with either HCl or NaOH. An adenylate deaminase activity was found to be present in the cytosolic S-100 of cells harvested during the onset of development, and this deaminase activity was greatly stimulated by ATP. With FoAMP as the substrate, an apparent Km of 236 microM and Vmax of 2.78 mumol min-1 mg-1 were observed. The deamination of FoAMP could be inhibited by the addition of the natural substrate AMP. An apparent Ki value of 136 microM was determined from initial rate data. An adenylosuccinate synthetase activity was observed to have a Km value for GTP, IMP, and aspartic acid of 23, 34, and 714 microM, respectively. The formycin analog FoIMP was not a substrate with this activity but was a competitive inhibitor of IMP. Finally hypoxanthine-guanine phosphoribosyltransferase was found to have Km and Vmax values for hypoxanthine of 55.5 microM and 34.3 nmol-1 min-1 mg-1. When guanine was used as the substrate, the rate of nucleotide formation was 50% that with hypoxanthine as the substrate. The advantages of using HPLC to examine the interconnecting activities of a multienzyme complex in subcellular fractions are discussed, including the increased sensitivity obtained by using formycin analogs in the assay procedures.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Intermediary purine-metabolizing enzymes from the cytosol of Dictyostelium discoideum monitored by high-performance liquid chromatography. 642 68

A novel mechanism of resistance to the antileukemic agent 6-thioguanine (TGua) was demonstrated in a clone (TGuo-30-2) derived from HL-60 human acute promyelocytic leukemia cells. The clone was isolated by prescreening mutagenized HL-60 cells in hypoxanthine-amethopterin-thymidine medium, followed by selection with 6-thioguanosine. TGuo-30-2 cells were cross-resistant to TGua and beta-2'-deoxythioguanosine. TGuo-30-2 cells exhibited a marked decrease in the capacity to accumulate intracellular TGua nucleotides after treatment with TGua. The decrease in accumulation was not caused by a defect in transport, a lack or alteration of hypoxanthine-guanine phosphoribosyltransferase activity, or enhanced degradation of TGua nucleotides but appeared to be due to the maintenance of a lowered level of 5-phosphoribosyl 1-pyrophosphate (PRPP) in the resistant variant, which corresponded to 20% of the parental concentration. Despite the decrease in PRPP levels, incorporation of glycine into purine nucleotides was greater in TGuo-30-2 than in parental cells. Measurement of PRPP amidotransferase activity using cell homogenates revealed altered kinetics for the enzyme from TGuo-30-2 cells, which included significant loss of sensitivity to feedback inhibition by 6-thioguanosine 5'-phosphate and greater catalytic activity at low concentrations of PRPP.
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PMID:Altered 5-phosphoribosyl 1-pyrophosphate amidotransferase activity in 6-thioguanine-resistant HL-60 human acute promyelocytic leukemia cells. 658 43

Acyclovir [9-(2-hydroxyethoxymethyl)guanine], a clinically useful anti-herpesvirus agent, was a weak inhibitor (Ki = 190 microM) of hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) from human erythrocytes. Nevertheless, this acyclic nucleoside analog was a more effective inhibitor than were its natural counterparts, guanosine (Ki = 1400 microM) and deoxyguanosine (Ki = 570 microM). The two oxidized metabolites of acyclovir, 9-carboxymethoxymethylguanine (Ki = 720 microM) and 8-hydroxy-9-(2-hydroxyethoxymethyl)guanine (Ki greater than 2000 microM), were less inhibitory than was the parent drug. None of the phosphorylated metabolites of acyclovir was as potent an inhibitor of HGPRTase as was GMP (Ki = 4 microM). However, the Ki value for acyclovir monophosphate was similar to that of dGMP (12 microM). The Ki values for acyclovir diphosphate (8.3 microM) and triphosphate (30 microM) were less than those for dGDP (110 microM) and dGTP (140 microM). The levels of these phosphate esters of acyclovir in cultured monkey kidney (Vero) and human embryo fibroblast (WI38) cells exposed to therapeutic levels of the drug were well below the observed Ki values. However, in herpesvirus-infected WI38 cells the levels of the phosphate esters of acyclovir were high enough potentially to inhibit the enzyme. Although inhibition of this enzyme by the phosphorylated metabolites of acyclovir may occur in these infected cells, concentrations of the drug very much higher than the EC50 concentration were required to achieve inhibitory levels. It is, therefore, unlikely that this inhibition contributes significantly to the antiviral activity.
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PMID:Effects of acyclovir and its metabolites on hypoxanthine-guanine phosphoribosyltransferase. 663 69

We have examined the basis for the recently reported, but unexplained deficiency of S-adenosylhomocysteine hydrolase (AdoHcyase) in the erythrocytes of patients with genetic deficiencies of purine nucleoside phosphorylase and hypoxanthine-guanine phosphoribosyltransferase. We found that a hemolysate from a patient with purine nucleoside phosphorylase deficiency had only 7% of control AdoHcyase activity, conforming the original observation. Of the purine nucleosides known to accumulate in nucleoside phosphorylase-deficient patients, inosine alone caused the phosphate-dependent, irreversible inactivation of purified human placental AdoHcyase, and of AdoHcyase in intact erythrocytes and cultured lymphoblastoid cells. Hypoxanthine did not inactivate purified AdoHcyase, but potentiated the effect of inosine in intact hypoxanthine-guanine phosphoribosyltransferase-deficient human lymphoblastoid cells. This presumably resulted from the ability of hypoxanthine to shift the equilibrium of the nucleoside phosphorylase reaction, preventing inosine breakdown. This could account for the partial AdoHcyase deficiency reported in hypoxanthine-guanine phosphoribosyltransferase-deficient patients. We have also demonstrated the AdoHycase-catalyzed synthesis of S-inosylhomocysteine from inosine and L-homocysteine, a reaction which may occur in nucleoside phosphorylase-deficient patients.
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PMID:Proposed explanation for S-adenosylhomocysteine hydrolase deficiency in purine nucleoside phosphorylase and hypoxanthine-guanine phosphoribosyltransferase-deficient patients. 678 20

Human DNA purified from HeLa cells and from three strains of skin fibroblasts was precipitated with calcium phosphate and added to mouse cells that were deficient in adenine phosphoribosyltransferase (APRT) and hypoxanthine phosphoribosyltransferase (HPRT). Selection for cells possessing either of the phosphoribosyltransferases was imposed by blocking de novo synthesis of purine nucleotides with azaserine in a medium supplemented with adenine and hypoxanthine. The frequency of colony formation after selection was 1.7 x 10(-7)-3.3 x 10(-6). Excepting some azaserine-resistant colonies that appeared only in the first experiment and infrequent revertants expressing moust APRT, all characterized clones expressed the human forms of APRT or HPRT according to the criteria of specific immunoprecipitation and electrophoretic mobility. The frequency of transfer of the human APRT gene was much greater than that of HPRT. Transfer efficiency was not significantly reduced when HeLa DNA was sheared to 6.5-13.5 kb size or when the donor DNA was isolated from a transferent that expressed human APRT.
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PMID:Expression of human genes for adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase after genetic transformation of mouse cells with purified human DNA. 699 64

Thiopurinol [4-thiopyrazolo(3.4-dyprimidine, TPP] and its ribonucleoside (TPPR) were effective in vitro against the intracellular and extracellular forms of L. braziliensis and L. mexicana. They also inhibited the transformation of the amastigote of L. donovani to the promastigote. These thio-analogues had about the same activity as allopurinol [4-hydroxypyrazolo(3.4-d)pyrimidine, HPP] and its ribonucleoside (HPPR). the thiopyrazolopyrimidines were converted primarily to the ribonucleoside-5' -phosphate (TPPR-MP) and to an unidentified metabolite, but not to any of the adenine ribonucleoside analogues previously shown to be formed from allopurinol and its ribonucleoside. There was an antagonism between the growth-inhibitory effects of allopurinol and thiopurinol. This is consistent with the findings that the intracellular concentrations of TPP and TPPR-MP are sufficient to inhibit the conversion of allopurinol to allopurinol ribonucleotide (HPPR-MP) by the hypoxanthine-guanine phosphoribosyltransferase by 30 per cent and the amination of HPPR-MP by adenylosuccinate synthetase by 50 per cent respectively. Consequently, the incorporation of the aminated product (aminopyrazolopyrimidine) into RNA was substantially decreased. The difference in metabolism between the thio- and hydroxypyrazolopyrimidines suggests a difference in their mechanisms of action against the pathogenic leishmania.
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PMID:Antileishmanial action of 4-thiopyrazolo (3.4-d) pyrimidine and its ribonucleoside. Biological effects and metabolism. 707 76


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