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)

The metabolic pathways of pterin de novo synthesis, interconversion and salvage which lead to the tetrahydrobiopterin cofactor of phenylalanine 4-monooxygenase, tyrosine 2-monooxygenase and tryptophan 5-monooxygenase are reviewed and data on the enzymes which catalyze the individual steps are presented. Analogies drawn between the inborn errors of tetrahydrobiopterin production and the Lesch-Nyhan syndrome, in which purine salvage is deficient, are used as a basis for the hypothesis that the neurological manifestations of the Lesch-Nyhan syndrome are due to neurotransmitter imbalance which stems from an imbalance of the aromatic amino acid monooxygenase activities which are themselves due to impaired pterin biosynthesis. The latter arises because, in the absence of the hypoxanthine phosphoribosyltransferase catalyzed purine salvage pathway, the supply of GTP for the GTP cyclohydrolase reaction, which is the first reaction on the pterin de novo synthesis pathway, is reduced. It is proposed that the different aromatic amino acid monooxygenases are differentially affected by this constrained pterin production. The activities of those most directly related to the quantal production of the cerebral neurotransmitters dopamine, norepinephrine and 5-hydroxytryptamine are affected whereas liver phenylalanine 4-monooxygenase activity is not overtly impaired. The results of different lines of research which support this concept are cited, as is direct evidence for a selective reduction of dopamine production in the basal ganglia of patients with the Lesch-Nyhan syndrome. It is proposed that lack of GMP for functions, other than its role in pterin de novo synthesis, accounts for the features of the Lesch-Nyhan syndrome which do not occur when only tetrahydrobiopterin production is deficient as in the inborn errors of tetrahydrobiopterin synthesis.
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PMID:Defects of tetrahydrobiopterin synthesis and their possible relationship to a disorder of purine metabolism (the Lesch-Nyhan syndrome). 286 76

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

Giardia lamblia, a flagellated parasitic protozoan and the causative agent of giardiasis, lacks de novo purine biosynthesis and exists on salvage of adenine and guanine by adenine phosphoribosyltransferase and guanine phosphoribosyltransferase. Guanine phosphoribosyltransferase from G. lamblia crude extracts has been purified to apparent homogeneity by Sephacryl S-200 gel filtration followed by C-8-GMP-agarose and 2',3'-GMP-agarose affinity chromatography, resulting in an overall recovery of 77% and a purification of 83,000-fold. The molecular weight of the native enzyme as estimated by gel filtration and isokinetic sucrose gradients was found to be 58,000-63,000, with a subunit molecular weight of approximately 29,000, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Mono P chromatofocusing chromatography gives rise to a major activity peak eluting from the column at a pH of 6.75 and two minor activity peaks at pH of 5.3 and 5.2. Hypoxanthine and xanthine can be recognized by the enzyme as substrates but at Km values 20 times higher than that observed with guanine. G. lamblia guanine phosphoribosyltransferase is immunologically distinct from human hypoxanthine-guanine phosphoribosyltransferase and Escherichia coli xanthine-guanine phosphoribosyltransferase, and G. lamblia DNA fragments are incapable of hybridizing with mouse neuroblastoma hypoxanthine-guanine phosphoribosyltransferase DNA or E. coli xanthine phosphoribosyltransferase DNA under relatively relaxed conditions. All evidence presented suggests that G. lamblia guanine phosphoribosyltransferase may be qualified as a potential target for antigiardiasis chemotherapy.
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PMID:Purification and characterization of guanine phosphoribosyltransferase from Giardia lamblia. 308 75

A simple and rapid spectrophotometric assay for the estimation of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity in human tissues is described. It is based on the increase in absorbance at 257.5 nm which occurs when the substrate guanine is converted to its 5'-mononucleotide, GMP. The assay has been developed to measure HGPRT activity in erythrocyte and lymphocyte lysates and in brain homogenates, and has been used in the screening of patients with hyperuricaemia and/or hyperuricosuria for HGPRT deficiency. It has also been used to determine the steady-state kinetic constants of a mutant form of the enzyme. The spectrophotometric assay is compared with the radioactive assay currently used to measure HGPRT activity.
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PMID:Human hypoxanthine-guanine phosphoribosyltransferase. Development of a spectrophotometric assay and its use in detection and characterization of mutant forms. 358 73

1. The purine bases adenine, hypoxanthine and guanine were rapidly incorporated into the nucleotide fraction of Ehrlich ascites-tumour cells in vivo. 2. The reaction of 5'-phosphoribosyl pyrophosphate with adenine phosphoribosyltransferase from ascites-tumour cells (K(m) 6.5-11.9mum) was competitively inhibited by AMP, ADP, ATP and GMP (K(i) 7.5, 21.9, 395 and 118mum respectively). Similarly the reactions of 5'-phosphoribosyl pyrophosphate with both hypoxanthine phosphoribosyltransferase and guanine phosphoribosyltransferase (K(m) 18.4-31 and 37.6-44.2mum respectively) were competitively inhibited by IMP (K(i) 52 and 63.5mum) and by GMP (K(i) 36.5 and 5.9mum). 3. The nucleotides tested as inhibitors did not appreciably compete with the purine bases in the phosphoribosyltransferase reactions. 4. It was postulated that the purine phosphoribosyltransferases of Ehrlich ascites-tumour cells may be effectively separated from the adenine nucleotide pool of these cells.
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PMID:Inhibition of purine phosphoribosyltransferases from Ehrlich ascites-tumour cells by purine nucleotides. 596 81

1. The progress curves of adenine phosphoribosyltransferase and of hypoxanthine phosphoribosyltransferase activity plotted against 5-phosphoribosyl pyrophosphate concentration were hyperbolic in nature. The inhibition of the former enzyme by AMP and GMP and of the latter enzyme by IMP and GMP showed completely competitive characteristics. 2. The effect of temperature on the reaction of adenine phosphoribosyltransferase and of hypoxanthine phosphoribosyltransferase was examined. The energy of activation of the former enzyme decreased at temperatures greater than 27 degrees and that of the latter enzyme at temperatures greater than 23 degrees . For each enzyme, the change in the heat of formation of the 5-phosphoribosyl pyrophosphate-enzyme complex at the critical temperature was approximately equal to the change in the energy of activation but was in the opposite direction. The inhibitor constants with both enzymes in the presence of nucleotides varied in different ways with temperature from the Michaelis constants for 5-phosphoribosyl pyrophosphate indicating that different functional groups were involved in binding substrates and inhibitors. 3. ATP was found to stimulate adenine-phosphoribosyltransferase activity at concentrations less than about 250mum and to inhibit the enzyme at concentrations greater than 250mum. The stimulation was unaffected by 5-phosphoribosyl pyrophosphate concentration but the inhibitory effect could be overcome by increasing concentrations of this compound. At low concentrations ATP reversed the inhibition of adenine phosphoribosyltransferase by AMP and GMP to an extent dependent on their concentration. 4. The properties of adenine phosphoribosyltransferase changed markedly on purification. Crude extracts of ascites-tumour cells had Michaelis constants for 5-phosphoribosyl pyrophosphate and adenine 75 and six times as high respectively as those obtained with purified enzyme. ATP had no stimulatory effect on activity of the purified enzyme or on that of crude extracts heated 15min. or longer at 55 degrees . 5. It is suggested that at low concentrations ATP is bound to an ;activator' site which is separate from the substrate binding site of adenine phosphorytransferase and that at high concentrations ATP competes with 5-phosphoribosyl pyrophosphate at the active site of the enzyme.
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PMID:Studies on the nature of the regulation by purine nucleotides of adenine phosphoribosyltransferase and of hypoxanthine phosphoribosyltransferase from Ehrlich ascites-tumour cells. 606 4

A facile and rapid purification procedure, based upon the heat denaturation of extraneous proteins and GMP-Sepharose affinity chromatography, has been used to purify hypoxanthine phosphoribosyltransferase from human brain. A homogeneous enzyme preparation, as judged by sodium dodecyl sulfate and gradient polyacrylamide gel electrophoresis, was obtained. The subunit molecular weight of the enzyme was estimated as 24,000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The native molecular weight, determined by gradient gel electrophoresis, was approximately 100,000. These results suggest human brain hypoxanthine phosphoribosyltransferase is a tetramer, consistent with recent results reported for the human erythrocyte enzyme. At least three charge variant forms of the human brain enzyme were distinguished by nondenaturing polyacrylamide gel electrophoresis, electrofocusing, and chromatofocusing. Acidic pI values of approximately 5.7, 5.5, and 5.0 were estimated for the three major species.
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PMID:Hypoxanthine phosphoribosyltransferase from human brain: purification and partial characterization. 609 78

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 isolation and characterization of a mutant mouse T-cell lymphoma (S49) with altered purine metabolism is described. This mutant, AU-100, was isolated from a mutagenized population of S49 cells by virtue of its resistance to 0.1 mM 6-azauridine in semisolid agarose. The AU-100 cells are resistant to adenosine mediated cytotoxicity but are extraordinarily sensitive to killing by guanosine. High performance liquid chromatography of AU-100 cell extracts has demonstrated that intracellular levels of GTP, IMP, and GMP are all elevated about 3-fold over those levels found in wild type cells. The AU-100 cells also contain an elevated intracellular level of pyrophosphoribosylphosphate (PPriboseP), which accounts for its resistance to adenosine. However AU-100 cells synthesize purines de novo at a rate less than 35% of that found in wild type cells. Furthermore, the intact cells of this mutant S49 cell line cannot efficiently incorporate labeled hypoxanthine into nucleotides since the salvage enzyme HGPRTase is inhibited in situ. The AU-100 cell line was found to be 80% deficient in adenylosuccinate synthetase, but these cells are not auxotrophic for adenosine or other purines. The significant alterations in the control of purine de novo and salvage metabolism caused by the defect in adenylosuccinate synthetase are mediated by the resulting increased levels of guanosine nucleotides.
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PMID:Abnormal regulation of purine metabolism in a cultured mouse T-cell lymphoma mutant partially deficient in adenylosuccinate synthetase. 615 49

Guanine is transported into germinated conidia of Neurospora crassa by the general purine base transport system. Guanine uptake is inhibited by adenine and hypoxanthine but not xanthine. Guanine phosphoribosyltransferase (GPRTase) activity was demonstrated in cell extracts of wild-type germinated conidia. The Km for guanine ranged from 29 to 69 micro M in GPRTase assays; the Ki for hypoxanthine was between 50 and 75 micro M. The kinetics of guanine transport differ considerably from the kinetics of GPRTase, strongly suggesting that the rate-limiting step in guanine accumulation in conidia is not that catalyzed by GPRTase. Efflux of guanine or its metabolites appears to have little importance in the regulation of pools of guanine or guanine nucleotides since very small amounts of 14C label were excreted from wild-type conidia preloaded with [8-14C]guanine. In contrast, excretion of purine bases, hypoxanthine, xanthine, and uric acid appears to be a mechanism for regulation of adenine nucleotide pools (Sabina et al., Mol. Gen. Genet. 173:31-38, 1979). No label from exogenous [8-14C]guanine was ever found in any adenine nucleotides, nucleosides, or the base, adenine, upon high-performance liquid chromatography analysis of acid extracts from germinated conidia of wild-type of xdh-l strains. The 14C label from exogenous [8-14C]guanine was found in GMP, GDP, GTP, and the GDP sugars as well as in XMP. Xanthine and uric acid were also labeled in wild-type extracts. Similar results were obtained with xdh-l extracts except that uric acid was not present. The labeled xanthine and XMP strongly suggest the presence of guanase and xanthine phosphoribosyltransferase in germinated conidia.
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PMID:Guanine uptake and metabolism in Neurospora crassa. 617


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