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)

Hypoxanthine phosphoribosyltransferase (IMP:pryophosphate phosphoribosyltransferase, EC 2.4.2.8) from human erythrocytes has been purified 13 000-fold to apparent homogeneity. The native enzyme has a sedimentation coefficient of 5.9 S, determined by analytical ultracentrifugation, and a molecular weight of 81 000-83 000, determined by sedimentation equilibrium centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates a subunit molecular weight of 26 000, suggesting that the enzyme is a trimer. Isoelectric focusing resolves three peaks of enzyme activity at pH 5.6, 5.7 and 5.9. The amino acid composition of hypoxanthine phosphoribosyltrasferase is 17 Lys, 5 His, 12 Arg, 0 Trp, 31 Asx, 12 Thr, 14 Ser, 16 Glx, 14 Pro, 19 Gly, 12 Ala, 5 Cys, 18 Val, 5 Met, 11 Ile, 20 Leu, 10 Tyr, and 9 Phe. The enzyme appears to have a blocked N terminus.
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PMID:Human hypoxanthine phosphoribosyltransferase. Purification and properties. 86 Dec 17

The change in genomic DNA responsible for HPRT deficiency has been determined in a patient with urate overproduction and gout. In erythrocyte cell lysates, this patient had approximately 10% of normal HPRT enzyme activity and 26% of immunoidentical HPRT protein. Cultured lymphoblasts derived from this patient were used to extract mRNA. This was reverse transcribed to cDNA, which was then amplified using the polymerase chain reaction. The resulting DNA was cloned and the nucleotide sequence determined. In addition a portion of the sequence was derived from cloned double-stranded cDNA prepared by conventional first and second strand synthesis. A single nucleotide base change (a C----T transition) was detected, which predicts an amino acid substitution of isoleucine for threonine at amino acid 168 of the HPRT protein. The nucleotide substitution creates a BamHI site, confirming a restriction fragment length polymorphism previously reported in this patient.
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PMID:Identification of a single nucleotide substitution in the coding sequence of in vitro amplified cDNA from a patient with partial HPRT deficiency (HPRTBRISBANE). 224 54

HPRT Ann Arbor is a variant of hypoxanthine (guanine) phosphoribosyl-transferase (HPRT: EC 2.4.2.8), which was identified in wo brothers with hyperuricemia and nephrolithiasis. In previous studies, this mutant enzyme was characterized by an increased Km for both substrates, a normal Vmax, a decreased intracellular concentration of enzyme protein, a normal subunit molecular weight and an acidic isoelectric point under native isoelectric focusing conditions. We have cloned a full-length cDNA for HPRT Ann Arbor and determined its complete nucleotide sequence. A single nucleotide change (T----G) at nucleotide position 396 has been identified. This transversion predicts an amino acid substitution from isoleucine (ATT) to methionine (ATG) in codon 132, which is located within the putative 5'-phosphoribosyl-1-pyrophosphate (PRPP)-binding site of HPRT.
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PMID:Identification of a single nucleotide change in a mutant gene for hypoxanthine-guanine phosphoribosyltransferase (HPRT Ann Arbor). 289 20

By means of a 5-bromodeoxyuridine (BrdU) incorporation and acridine orange fluorescence staining method we studied reactivation of the inactivated X chromosome (Xi) in newly formed cell hybrids between the near-diploid HPRT-deficient OTF9-63 murine embryonal carcinoma cell (ECC) with an XO sex chromosome constitution and the normal female mouse thymocyte. As reported earlier, most near-tetraploid hybrid cells were ECC in morphology and retained all chromosomes from both parents including three X chromosomes. Synchronization of the late replicating X chromosome in such hybrid cells, indicative of reactivation, was found for the first time on Day 3, and the frequency of reactivation was attained 90% on Day 5. Inhibition of cell cycle progression either by methylglyoxal bis(guanylhydrazone) dihydrochloride, an inhibitor of polyamine metabolism, or by isoleucine-deficient medium after cell fusion delayed reactivation of the Xi, which implied that the number of cell division cycles traversed by individual cells rather than the length of time after cell fusion is critical for the reactivation. Double-labeling experiments using [3H]thymidine and BrdU indicated that hybrid cells had undergone three or four mitoses before reactivation of the Xi. Most probably reactivation of the Xi is consequent to reversion of the thymocyte genome to an undifferentiated state under the influence of OTF9 genome. DNA demethylation or dilution of Xi-specific factors by mitoses may be involved in this process.
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PMID:Requirement of mitoses for the reversal of X-inactivation in cell hybrids between murine embryonal carcinoma cells and normal female thymocytes. 325 23

Branched-chain aminotransferase (BCT) catalyzes the reversible transamination of the branched-chain alpha-keto acids to the branched-chain L-amino acids. Since branched-chain L-amino acids (L-isoleucine, L-leucine, and L-valine) are essential for cell growth, cells which lack BCT were unable to proliferate in media containing alpha-keto acids in place of the corresponding L-amino acids. CHW-1102, a Chinese hamster cell line, lacks BCT and does not grow in alpha-keto acid media. Somatic cell hybrids were made by the fusion of CHW-1102 (HPRT-) with several human cell lines and isolated on HAT medium. Growth assays of hybrid clones on alpha-keto acid selection media independent of the HAT selection medium indicated two cell hybrid phenotypes: either (1) the hybrid clone, like the parental CHW-1102, could not utilize alpha-keto acid media, or (2) the hybrid could proliferate on all three alpha-keto acid media. The ability of hybrid cells to proliferate on alpha-keto acid media correlated with the presence of either of two human genes which independently complemented the Chinese hamster deficiency. Two human genes. BCT1 assigned to chromosome 12 and BCT2 assigned to chromosome 19, were demonstrated to code for the expression of two molecular forms of BCT.
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PMID:Branched-chain aminotransferase deficiency in Chinese hamster cells complemented by two independent genes on human chromosomes 12 and 19. 693 2

In an effort to further understand the pathogenesis of Lesch-Nyhan syndrome, an X-linked recessive disease of purine metabolism associated with a deficiency of hypoxanthine-guanine phosphoribosyltransferase, we have analyzed the amino acids in autopsy brain material obtained from five patients and six controls. The amino acids glycine and glutamine serve as substrates for the synthesis of purines in man. Amino acids were measured in the occipital cortex, limbic cortical area, cerebellar cortex, hippocampus and putamen. In general the amino acids were usually lower in concentration in brain material from affected individuals. Most dramatically decreased were threonine, serine, valine, isoleucine, lysine and arginine. Only glutamine and urea were higher than controls. Glutamate, gamma-aminobutyrate and cystathionine were essentially unaffected. The data reported here do not support a role for increased glycine in the pathogenesis of this disease as implied by findings previously reported in cultured cell lines (Skaper and Seegmiller 1976, 1977). The current findings suggest that individuals with Lesch-Nyhan syndrome have a generally lower concentration of free amino acids in brain. This decrease may be involved in the etiology of the disease or the decrease may be a result of the generally malnourished state of these individuals. These results imply that affected patients have a limited supply of amino acid precursors available for the synthesis of either proteins or neurotransmitters that the brain requires for normal function. Thus, the low amino acid pools could be an important factor in the brain dysfunction observed in patients with Lesch-Nyhan syndrome.
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PMID:Decreased amino acids in various brain areas of patients with Lesch-Nyhan syndrome. 713 31

Hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) from beef brain has been purified 3100-fold to apparent homogeneity using a purification procedure based on GMP-Sepharose affinity chromatography. The native enzyme has a molecular weight of 84,000 as determined by gel filtration studies. A subunit molecular weight of 26,000 was obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that the enzyme is a trimer. Two forms of the enzyme have been separated by nondenaturing polyacrylamide gel electrophoresis and isoelectric focusing. Basic pI values of 7.85 and 8.10 were obtained for the two forms. These values are much higher than have been observed with any other purified phosphoribosyltransferase. The amino acid composition of the enzyme is 18 Lys, 6 His, 9 Arg, 1 Trp, 6 Cys, 28 Asx, 12 Thr, 16 Ser, 19 Glx, 10 Pro, 23 Gly, 16 Ala, 17 Val, 5 Met, 11 Ile, 19 Leu, 9 Tyr, and 8 Phe. An unusual basic amino acid, yet to be identified, was also present. The enzyme exhibits Km values of 0.42 microM for guanine, 0.99 microM for hypoxanthine, 18.6 microM for P-Rib-PP in the presence of guanine, and 2.9 microM for P-Rib-PP in the presence of hypoxanthine.
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PMID:Studies of an unusually basic hypoxanthine-guanine phosphoribosyltransferase. 735 77

Guanine phosphoribosyltransferase from Giardia lamblia, a key enzyme in the purine salvage pathway, is a potential target for anti-giardiasis chemotherapy. Recent structural determination of GPRTase (Shi, W., Munagala, N. R., Wang, C. C., Li, C. M., Tyler, P. C., Furneaux, R. H., Grubmeyer, C., Schramm, V. L., and Almo, S. C. (2000) Biochemistry 39, 6781-6790) showed distinctive features, which could be responsible for its singular guanine specificity. Through characterizing specifically designed site-specific mutants of GPRTase, we identified essential moieties in the active site for substrate binding. Mutating the unusual Tyr-127 of GPRTase to the highly conserved Ile results in 6-fold lower K(m) for guanine. A L186F mutation in GPRTase increased the affinity toward guanine by 3. 3-fold, whereas the corresponding human HGPRTase mutant L192F showed a 33-fold increase in K(m) for guanine. A double mutant (Y127I/K152R) of GPRTase retained the improved binding of guanine and also enabled the enzyme to utilize hypoxanthine as a substrate with a K(m) of 54 +/- 15.5 microm. A triple mutant (Y127I/K152R/L186F) resulted in further increased binding affinity with both guanine and hypoxanthine with the latter showing a lowered K(m) of 29.8 +/- 4.1 microm. Dissociation constants measured by fluorescence quenching showed 6-fold tighter binding of GMP with the triple mutant compared with wild type. Thus, by increasing the binding affinity of 6-oxopurine, we were able to convert the GPRTase to a HGPRTase.
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PMID:Converting the guanine phosphoribosyltransferase from Giardia lamblia to a hypoxanthine-guanine phosphoribosyltransferase. 1097 10

Allelic loss is an important mutational mechanism in human carcinogenesis. Loss of heterozygosity (LOH) at an autosomal locus is one outcome of the repair of DNA double-strand breaks (DSBs) and can occur by deletion or by mitotic recombination. We report that mitotic recombination between homologous chromosomes occurred in human lymphoid cells exposed to densely ionizing radiation. We used cells derived from the same donor that express either normal TP53 (TK6 cells) or homozygous mutant TP53 (WTK1 cells) to assess the influence of TP53 on radiation-induced mutagenesis. Expression of mutant TP53 (Met 237 Ile) was associated with a small increase in mutation frequencies at the hemizygous HPRT (hypoxanthine phosphoribosyl transferase) locus, but the mutation spectra were unaffected at this locus. In contrast, WTK1 cells (mutant TP53) were 30-fold more susceptible than TK6 cells (wild-type TP53) to radiation-induced mutagenesis at the TK1 (thymidine kinase) locus. Gene dosage analysis combined with microsatellite marker analysis showed that the increase in TK1 mutagenesis in WTK1 cells could be attributed, in part, to mitotic recombination. The microsatellite marker analysis over a 64-cM region on chromosome 17q indicated that the recombinational events could initiate at different positions between the TK1 locus and the centromere. Virtually all of the recombinational LOH events extended beyond the TK1 locus to the most telomeric marker. In general, longer LOH tracts were observed in mutants from WTK1 cells than in mutants from TK6 cells. Taken together, the results demonstrate that the incidence of radi-ation-induced mutations is dependent on the genetic background of the cell at risk, on the locus examined, and on the mechanisms for mutation available at the locus of interest.
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PMID:Different mechanisms of radiation-induced loss of heterozygosity in two human lymphoid cell lines from a single donor. 1122 43

We identified a novel point mutation (I137T) in the hypoxanthine-guanine phosphoribosyltransferase (HPRT; EC 2.4.2.8) encoding gene, in a patient with partial deficiency of the enzyme (variant of Lesch-Nyhan syndrome). The mutation, ATT to ACT, resulting in substitution of isoleucine to threonine, occurred at codon 137 (exon 6), which is within the region encoding the binding site for 5-phosphoribosyl-1-pyrophosphate (PRPP). We suggest the mechanism by which the mutation-induced structural alteration of HPRT reduced the affinity of the enzyme for PRPP.
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PMID:A novel point mutation (I137T) in the conserved 5-phosphoribosyl-1-pyrophosphate binding motif of hypoxanthine-guanine phosphoribosyltransferase (HPRTJerusalem) in a variant of Lesch-Nyhan syndrome. 1261 88


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