Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.7 (adenine phosphoribosyltransferase)
 692 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A group of enzymes known to be involved in group translocation-type transport mechanisms for the uptake of a variety of nucleotide precursors are enzymatically active both in their natural membrane milieu and in aqueous solution. The activity in aqueous solution markedly differ, however, from the enzymatic activity when the enzyme is membrane localized. The adenine phosphoribosyltransferase (PRT) of E. coli (Hochstadt-Ozer and Stadtman, 71a) is capable of carrying out an exchange reaction between the base moieties of adenine and AMP without requiring P-ribose-PP as an intermediate; the enzyme in aqueous solution requires P-ribose-PP, indicating a different reaction mechanism in the two environments. Like the adenine PRT of E. coli, the hypoxanthine PRT of Salmonella typhimurium (Jackman and Hochstadt, '76) also carried out an exchange reaction on the membrane only and also is more sensitive to a number of inhibitors in aqueous solution relative to the sensitivity when embedded in the membrane. In addition, however, the hypoxanthine PRT, while restricted to hypoxanthine as a substrate in the membrane, also accepts guanine as substrate in its soluble form. The membrane capacities reas determined in a guanine PRT deletion strain (Jackman and Hochstadt, '76). Finally, in mammalian cell lines purine nucleoside phosphorylase, which translocates the ribose moiety of inosine across the plasma membrane of mouse fibroblasts undergoes a 30-fold increase in substrate turnover number upon liberation from the membrane. These data raise two important caveats with respect to study of membrane enzymes and transport. Firstly, an enzyme once solubilized and found to differ kinetically from substrate transport in situ cannot be excluded from participating in translocations in the membrane on the basis of its activity in aqueous solution. Secondly, an enzyme which "appears" largely soluble upon cell rupture cannot be assumed to be a cycloplasmic enzyme because of majority of the solubilized activity may represent only a small fraction of the enzyme molecules highly activated concomitant to their solubilization. In this latter case the ability to activate enzyme still residing on the membrane (e.g., with detergents) would be necessary in order to estimate total membrane associated activity after cell rupture.
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PMID:The function and activity of certain membrane enzymes when localized on- and off- the membrane. 82 51

The significance of partial deficiency of erythrocyte adenine phosphoribosyltransferase (APRT), reported in a number of subjects with gout, has been investigated by studying its incidence in 700 normal blood donors. Three clearly deficient subjects were found, an incidence not significantly different from that in patients with abnormalities of urate metabolism. A new assay method for APRT is described in which an erythrocyte lysate is incubated with adenine and phosphoribosylpyrophosphate (PRPP) for a given time; both hemoglobin and adenine nucleotide (AMP) are then precipitated with lanthanum phosphate; the change in absorbance of adenine at 260 nm reflects the extent of its conversion to AMP by APRT.
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PMID:Adenine phosphoribosyltransferase: a simple spectrophotometric assay and the incidence of mutation in the normal population. 86 96

Erythrocytes, obtained from a normal adult male and from a patient with Lesch-Nyhan syndrome, were incubated with [8-14C]adenine and [8-14C]hypoxanthine (Table 1). The labeled adenine was utilized to about the same extent for the synthesis of AMP by the normal subject's and the patient's erythrocytes. Deamination of AMP to IMP occurred to about the same extent in both samples. In contrast, hypoxanthine was utilized extensively for IMP synthesis in the normal erythrocyte only. The amount of total label in the IMP was about 100 times that of the Lesch-Nyhan erythrocyte, a consequence of the deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity in the syndrome. No significant labeling of the AMP occurred. When aliquots of erythrocytes from both sources were incubated with 4-amino-5-imidazolecarboxamide (AICA) and sodium [14C]formate, extensive labeling of the IMP occurred in normal and in Lesch-Nyhan erythrocytes. The data suggest that AICA serves as a substrate for the adenine phosphoribosyltransferase (APRT) of the Lesch-Nyhan erythrocyte and that the ribotide of AICA, 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide (AICAR), undergoes formylation by labeled N10-formyl tetrahydrofolic acid formed from the reaction of sodium [14C]formate with the tetrahydrofolic acid of the cell. The formyl-AICAR undergoes ring closure to IMP by a series of reactions comparable to those described for the normal erythrocyte. When 5-amino-1-ribosyl-4-imidazolecarboxamide (rAICA) and sodium [14C]formate were incubated with erythrocyte suspensions, extensive utilization for IMP synthesis was also observed in normal erythrocytes and in erythrocytes from Lesch-Nyhan patients (Table 2). The reaction sequence is somewhat different from that of AICA. AICA is not a substrate for the purine nucleoside phosphorylase of rabbit or human erythrocytes. The mechanism of rAICA utilization is visualized as a direct phosphorylation of the ribosyl compound, possibly by the adenosine kinase of the human cell. The ribotide, AICAR, formed by this mechanism, undergoes formylation and ring closure, yielding IMP. The glutamine antagonist, diazooxonorleucine (DON), was added to aliquots of patients' cells incubated with rAICA and sodium [14C]formate. DON is an effective inhibitor of the conversion of IMP to GMP and its presence in an incubation suspension resulted in a somewhat greater radioactivity of the total cellular IMP. The extension of the current studies to Lesch-Nyhan cells in culture may serve to assist in the direct evaluation of the regulatory role of IMP in the de novo pathway of purine nucleotide biosynthesis. Because of the substrate requirements of the reactions, the metabolism of AICA and rAICA may also serve to differentiate the roles of purine nucleotides and of phosphoribosylpyrophosphate (PRPP) in the pathway regulation. The findings presented also offer a possible therapeutic approach to the early treatment of the disease in the afflicted neonate...
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PMID:Lesch-Nyhan syndrome: the synthesis of inosine 5'-phosphate in the hypoxanthine-guanine phosphoribosyltransferase-deficient erythrocyte by alternate biochemical pathways. 87 Aug 76

Adenine and adenosine metabolism has been studied in intact human erythrocytes in vitro using high performance liquid chromatography, isotopic labeling and electrophoresis. Their metabolism to nucleotides was controlled by phosphoribose diphosphate synthesis which was phosphate dependent. Adenosine formed hypoxanthine or IMP depending upon Pi concentration, but adenosine kinase and deaminase activities were not affected by P levels. Free [14C]adenine and [14C]hypoxanthine were found in cellular extracts. Rapid interconversions occurred to give a distribution for ATP : ADP : AMP of 10 : 1 : 0.1. Marked decomposition of ATP to ADP and AMP occurred during incubations in plasma and Earle's media in air on nitrogen, but ATP levels remained stable in phosphate buffers and in the presence of oxygen. At physiological Pi (1 mM) adenosine kinase activity grossly exceeded adenine phosphoribosyltransferase activity. The latter was approximately 7 fold that of hypoxanthine phosphoribosyltransferase activity. These differences decreased with increasing Pi levels. No significant increase in corresponding nucleotides was obtained by incubation with high levels (0.5 mM) of adenine, guanine or guanosine at physiological Ii, ATP increased by 10% independently of the substrate employed and significant amounts of IMP and GTP were formed adenosine and guanosine, respectively. The existence of a bound intracellular pool of ATP is suggested.
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PMID:Studies on adenine and adenosine metabolism by intact human erythrocytes using high performance liquid chromatography. 94 98

Mutants of Chinese hamster ovary cells deficient in glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP 1-oxidoreducatse, EC 1.1.1.49) activity were isolated after mutagenesis with ethyl methane sulfonate. The mutants were induced at frequencies of about 10-4 and do not differ in growth properties from wild-type cells. They were isolated by means of a sib selection technique coupled with a histochemical stain of colonies for enzyme activity. The lack of enzyme activity is not due to a dissociable inhibitor, and is recessive in hybrid cells. Multiple mutants that lack hypoxanthine phosphoribosyltransferase activity (IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) and adenine phosphoribosyltransferase activity (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7) were isolated by further mutagenesis. By following segregation of wild-type phenotypes from heterozygous multiply marked hybrid cells, it was shown that the genes responsible for glucose-6-phosphate dehydrogenase activity and hypoxanthine phosphoribosyltransferase activity are linked in Chinese hamster cells, in agreement with the location of both on the X chromosome in humans. No linkage to adenosine phosphoribosyltransferase was found. The isolation of mutant cells carrying linked markers should prove useful for studying chromosomal events such as segregation, breakage, recombination, and X-chromosome reactivation.
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PMID:Isolation of mammalian cell mutants deficient in glucose-6-phosphate dehydrogenase activity: linkage to hypoxanthine phosphoribosyl transferase. 105 32

Evidence for derepression of the gene for hypoxanthine phosphoribosyltransferase (HPRT; IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) on the human inactive X chromosome was obtained in hybrids of mouse and human cells. The mouse cells lacked HPRT and were also deficient in adenine phosphoribosyltransferase (APRT; AMP: pyrophosphate phosphoribosyltransferase; EC2.4.2.7). The human female fibroblasts were HPRT-deficient as a consequence of a mutation on the active X but contained a normal HPRT gene on the inactive X. The two human X chromosomes were further distinguished by differences in morphology: the inactive X was morphologically normal while the active X included most of the long arm of autosome no. 1 translocated to the distal end of the X long arm. Forty-one hybrid clones were first isolated by selection for the presence of APRT; when these clones were selected for HPRT, six of them yielded derivatives having human HPRT with incidences of about 1 in 10-6 APRT-selected hybrid cells. The HPRT-positive derivatives contained a normal-appearing X chromosome indistinguishable from the inactive X of the parental human fibroblasts. The active X with the translocation was not found in any of the HPRT-positive hybrid cells. Human phosphoglycerokinase (ATP:3-phospho-D-glycerate 1-phosphotransferase. EC 2.7.2.3) and glucose-6-phosphate dehydrogenase (D-glucose 6-phosphate: NADP 1-oxidoreductase, EC 1.1.1.49), which are specified by X-chromosomal loci, were not detected in the hybrids expressing HPRT even though they contained an apparently intact X chromosome. The observations are most simply explained by the infrequent, stable derepression of inactive X chromosome segments that include the HPRT locus but not the phosphoglycerokinase and glucose-6-phosphate dehydrogenase loci.
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PMID:Localized Derepression on the Human Inactive X Chromosone in Mouse-Human Cell Hybrids. 105 21

Permanent transfer of genetic information from chromosomes isolated from human diploid cells to recipient cells has been demonstrated. Human metaphase chromosomes were incubated with mouse A9 fibroblasts deficient in hypoxanthine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) and adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7). Colonies of cells containing hypoxanthine phosphoribosyltransferase appeared during growth in a selective medium. The hypoxanthine phosphoribosyltransferase gene product in four independent colonies was identified as human donor species by both gel electrophoresis and isoelectric focusing; hence these colonies did not result from reversion of ta9 parental cells. Other X-linked human genes, glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NAD(+) 1-oxidoreductase, EC 1.1.1.49) and phosphoglycerate kinase (ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3), were not expressed in these same colonies. Dissociation of expression of these X-linked genes probably results from chromosomal fragmentation during uptake, but other mechanisms have not been excluded.
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PMID:Human gene expression in rodent cells after uptake of isolated metaphase chromosomes. 105 70

A mouse embryonal carcinoma cell line isolated for resistance to the adenine analogue 2,6-diaminopurine (DAP) was found to have near-wild-type levels of adenine phosphoribosyltransferase (APRT) activity in a cell-free assay. This DAP-resistant (DAPr) cell line, termed H29D1, also exhibited near-wild-type levels of adenine accumulation and the ability to grow in medium containing azaserine and adenine. Growth in this medium requires high levels of intracellular APRT activity. Using the polymerase chain reaction (PCR) and the dideoxy chain termination sequencing technique, an A-->G transition was discovered in exon 3 of the aprt gene in H29D1. This mutation resulted in an Arg-to-Gln change at amino acid 87 of the APRT protein that, in turn, resulted in a decreased affinity for adenine. An increased sensitivity of APRT to inhibition by AMP was observed when comparing H29D1 to P19, the parental cell line. Using a transgene containing the A-->G mutation, we demonstrated that this mutation is responsible for the biochemical and cellular phenotypes observed for the H29D1 cell line. The approach used in this study provides a definitive method for linking a mutation to a specific cellular phenotype.
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PMID:Molecular and biochemical elucidation of a cellular phenotype characterized by adenine analogue resistance in the presence of high levels of adenine phosphoribosyltransferase activity. 129 76

Five purine auxotrophic mutants of Lactococcus lactis were isolated. L. lactis was capable of converting adenine, guanine and hypoxanthine to AMP, GMP and IMP, respectively, indicating the existence of adenine phosphoribosyltransferase (APRT) and hypoxanthine guanine phosphoribosyltransferase (HGPRT) activities. A 1.3 kb DNA fragment from L. lactis was cloned by complementation of the hpt mutation in Escherichia coli. Introduction of this fragment into L. lactis resulted in an increase in HGPRT activity. In vitro transcription and translation analysis showed that the fragment coded for a polypeptide with M(r) of 22,000. The nucleotide sequence of this hpt gene was determined.
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PMID:Isolation of purine auxotrophic mutants of Lactococcus lactis and characterization of the gene hpt encoding hypoxanthine guanine phosphoribosyltransferase. 146 8

A novel method for measuring AMP-deaminase activity in human erythrocytes is presented, based on the determination of the reaction product, IMP, using high performance liquid chromatography. IMP formation was found to be proportional both to the incubation time and the amount of haemolysate over a wide range. The minimal detectable AMP-deaminase activity was more than 1000 times lower than the mean activity found in healthy controls (1083 nmol/h/mg Hb). No marked difference of activity was found in the patients with the following inherited purine disorders: familial juvenile gouty nephropathy and deficiencies of adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase or adenine phosphoribosyltransferase. The activity in the erythrocytes of patients with chronic renal failure was also similar to controls. The existence of subjects with low erythrocyte AMP-deaminase activity in the population has been confirmed.
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PMID:A high performance liquid chromatographic assay for AMP-deaminase activity in the erythrocytes of healthy subjects and patients with inherited purine disorders. 191 25


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