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)

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 behavioral responses to separate and combined administration of the D1 agonist SKF-38393 and the D2 agonist quinpirole following acute dopamine (DA) depletion via alpha-methyl-p-tyrosine (AMPT) or AMPT/reserpine were examined in infant (10-day-old) and weanling (21-day-old) rat pups. At both ages, AMPT pretreatment generally had little impact on D1- or D2-agonist-induced responding, whereas the greater DA depletion observed following AMPT/reserpine pretreatment was generally associated with suppression of both D1 and D2-agonist-typical responding. Thus, whereas in adult animals some degree of D1 receptor activation by endogenous dopamine appears to be necessary for D2 responding but not vice versa (e.g. White et al. 1988), in young animals there appears to be a reciprocal co-dependence of these two receptor subtypes, with extensive DA depletion suppressing responding to both agonists when administered separately. At 10 days of age, some D1 and D2 agonist-induced behaviors that were previously blocked by AMPT/reserpine were reinstated following combined administration of both agonists. In contrast, no clear evidence for reinstatement was seen following administration of the combined agonists to AMPT/reserpine-pretreated weanlings, perhaps due to the induction of potential competing behaviors. Whereas DA depletion blocked many D1- and D2-induced behaviors, such depletion conversely promoted the expression in agonist-treated animals of a number of behaviors that were not normally induced by the agonists in non-depleted animals. These behaviors typically involved an oral component and included grooming and mouthing following SKF-38393 in depleted 10-day-old pups, mouthing following administration of either agonist to depleted weanlings, and probing and intense self-mutilation (forepaw and tongue biting) following the combined agonists in depleted weanlings. This rapid induction of potentiated agonist responsiveness following acute DA depletion early in life may have significant implications with regard to animal models for the developmental disorder of Lesch-Nyhan syndrome.
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PMID:Effects of acute dopamine depletion on responsiveness to D1 and D2 receptor agonists in infant and weanling rat pups. 135 Mar 50

The Lesch-Nyhan syndrome is a neurogenetic disorder caused by congenital deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). The disorder is characterized by prominent neurobehavioral abnormalities which appear to result in part from dysfunction of striatal dopamine systems. HPRT-deficient (HPRT-) mutant strains of mice have been produced as animal models for this syndrome, but these animals exhibit none of the neurobehavioral abnormalities seen in Lesch-Nyhan patients. The present studies describe the behavioral responses of three strains of mice carrying one of two mutations in the HPRT gene to agents which interact with brain dopamine systems. HPRT- mice are more sensitive than age- and sex-matched littermates to the motor-activating properties of dopamine-releasing agents (amphetamine, amfonelic acid and methylphenidate), but not dopamine uptake inhibitors (GBR 12909 and nomifensine). The enhanced sensitivity of the HPRT- mice to the dopamine-releasing agents is not caused by dopamine receptor supersensitivity, because the HPRT- mice do not show enhanced motor responses to the direct D1/D2 dopamine receptor agonist apomorphine or to the selective D1 dopamine receptor agonist SKF 38393. The function of regulatory dopamine autoreceptors, as assessed by suppression of spontaneous motor activity by low doses of R(-)-propylnorapomorphine, also appears normal in the HPRT- mice. Biochemical analysis shows that the HPRT- mice have significantly lower levels of dopamine (-45%), but normal levels of tyrosine, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine in the caudoputamen. In contrast to the deficit in caudoputamen dopamine, no deficits were noted in the accumbens of the HPRT- mice. These results indicate the existence of an inherent abnormality in the dopamine systems in the brains of HPRT- mice, despite their apparently normal spontaneous behavior.
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PMID:Functional analysis of brain dopamine systems in a genetic mouse model of Lesch-Nyhan syndrome. 143 91

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

Treatment of hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-deficient human promyelocytic leukemia (HL-60) cells with 6-thioguanine results in growth inhibition and cell differentiation. 6-Thioguanine is a substrate for the tRNA modification enzyme tRNA-guanine ribosyltransferase, which normally catalyzes the exchange of queuine for guanine in position 1 of the anticodon of tRNAs for asparagine, aspartic acid, histidine, and tyrosine. During the early stages of HGPRT-deficient HL-60 cell differentiation induced by 6-thioguanine, there was a transient decrease in the queuine content of tRNA, and changes in the isoacceptor profiles of tRNA(His) indicate that 6-thioguanine was incorporated into the tRNA in place of queuine. Reversing this structural change in the tRNA anticodon by addition of excess exogenous queuine reversed the 6-thioguanine-induced growth inhibition and differentiation. Similar results were obtained when 8-azaguanine (another inhibitor of queuine modification of tRNA that can be incorporated into the anticodon) replaced 6-thioguanine as the inducing agent. The data suggest a primary role for the change in queuine modification of tRNA in mediating the differentiation of HGPRT-deficient HL-60 cells induced by guanine analogs.
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PMID:Guanine analog-induced differentiation of human promyelocytic leukemia cells and changes in queuine modification of tRNA. 347 81

The free amino acid content in the cerebral cortex of rats administered caffeine orally, and with automutilation behavior similar to that observed in the Lesch-Nyhan syndrome, have been measured. Amino acids significantly elevated were taurine, histidine and aspartic acid, whereas tyrosine showed a significant reduction. There was no change in the concentration of gamma-aminobutyric acid and glutamic acid. It has been conjectured that changes in amino acids levels in the cortex might be responsible for the pharmacological action of caffeine and for the progressive behavior abnormalities observed in these rats. Interestingly these results are similar to these found recently in experimental uremia.
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PMID:Caffeine-induced changes in the composition of the free amino acid pool of the cerebral cortex. 404 83

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

Crystal structures of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) proteins have implied that the translocation of a flexible loop containing a highly conserved Ser-Tyr dipeptide is necessary for the protection of the proposed oxocarbonium ion transition state of the enzyme (Eads, J. C., Scapin, G. T., Xu, Y., Grubmeyer. C., and Sacchettini, J. C. (1994) Cell 78, 325-334; Schumacher, M. A., Carter, D., Roos, D. S., Ullman, B., and Brennan, R. G. (1996) Nature Struct. Biol. 3, 881-887). An essential role for this Ser-Tyr dyad in HGPRT catalysis has now been verified biochemically and genetically for the Leishmania donovani HGPRT employing a combination of protein modifying reagents and site-directed mutagenesis. Incubation of HGPRT with either tetranitromethane or diethyl pyrocarbonate inactivated the enzyme completely, and peptide sequence analysis revealed that tetranitromethane treatment modified the Tyr residue within the Ser95-Tyr96 dipeptide. Analysis of site-directed mutants confirmed that both amino acids were vital for phosphoribosylation activity. Mutant HGPRTs, S95A, S95E, Y96F, and Y96V, exhibited dramatic reductions in their catalytic capabilities of 2-3 orders of magnitude, whereas HGPRTs containing conservative substitutions, S95C and S95T, displayed only a 2-3-fold decrease in kcat. Km values for the substrates of the forward and reverse reactions were largely unchanged for all HGPRT constructs, except for a 4-5-fold decrease in the Km value of the Y96F and Y96V mutants for phosphoribosylpyrophosphate. Expression of L. donovani hgprt constructs in Escherichia coli indicated that wild type and S95T HGPRTs complemented bacterial phosphoribosyltransferase deficiencies, whereas the S95A and S95C mutants complemented weakly, and the S95E, Y96F, and Y96V HGPRT did not support bacterial growth. These data authenticate that the Ser-Tyr dipeptide that is conserved among all members of the HGPRT family is essential for phosphoribosylation of purine nucleobases by HGPRT.
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PMID:The conserved serine-tyrosine dipeptide in Leishmania donovani hypoxanthine-guanine phosphoribosyltransferase is essential for catalytic activity. 908 19

The brains of two patients with Lesch-Nyhan syndrome (LNS) were studied. The concentration of dopamine was decreased in the caudate nucleus of LNS patients. Immunohistochemical methods revealed that the dopamine (DA) D1 and D2 receptor and methionine-enkephalin immunoreactivities (IRs) were increased in the putamen, and less significantly in the caudate nucleus. The D1 and D2 receptor IRs of the cingulate cortex, the tryptophan-hydroxylase IR in the dorsal nucleus of the midbrain, as well as the substance P and methionine-enkephalin IRs of the nociception-conducting structures, including the periaqueductal gray and spinal trigeminal nucleus, were not changed. Tyrosine-hydroxylase IR was not decreased in the substantia nigra of the LNS patients. Therefore, the cause of the decreased dopaminergic activity in LNS may not be involved in the production of tyrosine hydroxylase in the substantia nigra. Developmental abnormalities due to the DA defect at an early age might exist in the postsynaptic structure in the striatum.
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PMID:Dopamine receptor upregulation in Lesch-Nyhan syndrome: a postmortem study. 1040 87

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


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