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)

The molecular and biochemical aspects of purine nucleotide biosynthesis through de novo and salvage pathways, the production of uric acid, and their regulation mechanisms are reviewed for further understanding of hyperuricemia and gout. The metabolic rate of purine nucleotide biosynthesis is chiefly determined by the regulation of the de novo pathway, especially amidophosphoribosyltransferase and PRPP synthetase, and the accumulation of uric acid results from the acceleration of de novo biosynthesis and catabolism of purine nucleotide or the decrease in urinary excretion of uric acid. Moreover, several enzyme mutations of purine nucleotide metabolism are also clinically important including gout with hyperactive HPRT and the deficiency of HPRT (Lesch-Nyhan syndrome), adenylosuccinate lyase, xanthine oxidase, APRT, PNP, or ADA (SCID) with gene therapy.
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PMID:[Metabolism of purine nucleotides and the production of uric acid]. 897 90

The TK6 human B lymphoblastoid cell line contains two easily and widely used selectable markers: the X-linked, hemizygous hprt locus, and the heterozygous tk locus on chromosome 17q. In this study, rare APRT heterozygotes were directly isolated from the TK6 population by clonal selection in cell culture medium supplemented with 5 micrograms/ml of 8-azaadenine. One of nine isolated heterozygotes, AZH1, was characterized extensively. APRT- mutants can be recovered from AZH1 at a mutation rate of 1.5 x 10(-7), similar to rates previously determined for the selection of TK- and HPRT- mutants from TK6. A unique sequence alteration was identified in the non-functional aprt allele at position 1930. A G:C to A:T transition at this site alters the canonical AG splice acceptor dinucleotide in exon 3, and also results in the destruction of a Stul recognition sequence. This polymorphism was used to analyze loss of heterozygosity in a set of 32 spontaneous APRT- mutants by restriction analysis following PCR amplification. Analysis of flanking microsatellite dinucleotide polymorphisms demonstrated that LOH occurring in spontaneous APRT- mutants is nearly always a multi-locus event extending at least 7.5 cM along chromosome 16q. This pattern of LOH among APRT- mutants differs from extensive LOH in spontaneous, normal-growth TK- mutants derived from TK6 cells (p < 0.0001), and suggests that cis-acting factors may be equally important in shaping the mutational spectrum as trans-acting factors such as cellular apoptotic capacity.
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PMID:Isolation of an APRT heterozygote from TK6 human lymphoblasts: predominance of multi-locus loss of heterozygosity among spontaneous APRT-mutants. 921 76

We have recently detected de-novo transcripts of the predominantly muscle-specific myotonin protein kinase gene in human preimplantation embryos from the 1-cell to the 4-cell stages. Others have shown de-novo transcripts of the Y-linked genes, ZFY and SRY, in the 1-cell zygote. In order to assess the significance of early transcription of these predominantly tissue-specific genes in preimplantation development, we have analysed individual human oocytes and preimplantation embryos for the presence of transcripts of two further tissue-specific genes, alpha-globin and beta-globin, and two house-keeping genes, HPRT and APRT. Reverse transcriptase polymerase chain reaction assays were developed to the required single cell sensitivity, using human red blood cells and fibroblasts, prior to their application to human oocytes and embryos. As expected, transcripts of the house-keeping genes, HPRT and APRT, were detected at all stages of preimplantation development. Transcripts of 'tissue-specific' alpha-globin were readily detected in preimplantation embryos from the 1-cell stage. However, transcripts of beta-globin were detected only rarely (in only one of the 11 embryos analysed). This difference may be due to the fact that alpha-globin contains a CpG island. A survey of the data on gene expression in early human development suggests that CpG-island-containing genes may be expressed in preimplantation embryos. Expression of these genes in gametes and early embryos may be involved in the survival of CpG islands in evolution.
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PMID:Transcription of tissue-specific genes in human preimplantation embryos. 940 90

High energy phosphate levels fall rapidly during cardiac ischemia and recover slowly (more than one week) during reperfusion. The slow recovery of ATP may reflect a lack of purine metabolic precursors and/or increased activity of purine catabolic enzymes such as 5'-nucleotidase (5'-NT, EC 3.1.3.5) and adenosine deaminase (ADA, EC 3.5.4.4). The activity of enzymes involved in both the catabolism of ATP precursors (5-NT and ADA) and the restoration of ATP from slow synthetic pathways [adenosine kinase (AK, EC 2.7.1.20), adenine phosphoribosyl transferase (APRT, EC 2.4.2.7) and hypoxanthine phosphoribosyl transferase (HPRT, EC 2.4.2.8)] may directly affect the rate of ATP recovery. Strategies to enhance recovery will depend on the relative activity of these enzymes following ischemia. Their activity in different species and their response to ischemia are not well characterized. Hence, rapid assay methods for these enzymes would facilitate detailed time course studies of their activities in postischemic myocardium. We modified a single ion-exchange column chromatographic method using DEAE-Sephadex to determine the products of incubation of 5'-NT, AK, APRT and HPRT with their respective substrates. The uniformity of the final product measurement procedure for all assays permits the activities of the four enzymes to be rapidly determined in a single tissue sample and facilitates the study of a large number of samples. This technique should also be useful for enzymes of the pyrimidine metabolic pathway.
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PMID:Ion-exchange column chromatographic method for assaying purine metabolic pathway enzymes. 961 62

It has been reported that 9-ethyladenine (9-EA) is an efficient inhibitor of APRT (adenine phosphoribosyltransferase) and that its administration causes self-injurious behavior (Lesch-Nyhan Syndrome-like symptoms) in HPRT (hypoxanthine-guanine phosphoribosyltransferase)-deficient mice. In contrast, we found neither any self-injurious behavior (SIB), such as visible injury or hair loss, nor any apparent decrease in APRT activity in HPRT-deficient mice treated with 9-EA. We also found that 9-EA has little irreversible or competitive inhibitory effect on APRT in vitro, even at a concentration of 10(-2) M. In light of the negative finding of SIB in APRT/HPRT double-deficient mice, it seems unlikely that SIB in HPRT-deficient mice is caused by lowered APRT activity. It is concluded that 9-EA is not a sufficient APRT inhibitor and cannot be used in experiments that mimic lowered APRT status in an animal model.
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PMID:No self-injurious behavior was found in HPRT-deficient mice treated with 9-ethyladenine. 973 33

Current models suggest that genomic instability is crucial in the accumulation of the multiple alterations required for tumorigenesis. However, the nature of the initial damage responsible for the origin of genomic instability remains poorly understood. In this investigation we demonstrate that the nucleotide analog 2,6-diaminopurine (DAP) can be used to induce highly focused damage to the large blocks of paracentromeric heterochromatin on chromosomes 1, 9 and 16. A large fraction of cells exposed to DAP exhibit undercondensation of alpha and classical heterochromatin which persists into metaphase. Subsequent chromosome breakage was observed for one of the target chromosomes by preferential exclusion of chromosome 16 fragments into micronuclei (P < 0.0001). The specificity of DAP-induced chromosomal breakage enabled us to utilize it as a reagent to demonstrate that paracentromeric heterochromatin is a sensitive target for the induction of persistent genomic instability. We observed a 100-fold increase in mutagenesis affecting a chromosome 16 marker (APRT) compared with marker loci on chromosomes 17 (TK) or X (HPRT). We previously reported that APRT- mutants were recovered at a high rate upon selection in DAP in a process involving recombinationally mediated loss of heterozygosity that extends from the telomere to the boundary region of the paracentromeric heterochromatin. Karyotypic analysis of DAP-resistant APRT- mutant clones demonstrated extensive genomic instability, particularly evidence of multiple and sequential events affecting chromosome 16. These data suggest that the heterochromatic breakage observed cytogenetically immediately following DAP exposure is also responsible for the initiation of persistent genomic instability.
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PMID:Targeted breakage of paracentromeric heterochromatin induces chromosomal instability. 980 Jan 88

We constructed a subgenomic cosmid library of DNA replicated early in the S phase of normal human diploid fibroblasts. Cells were synchronized by release from confluence arrest and incubation in the presence of aphidicolin. Bromodeoxyuridine (BrdUrd) was added to aphidicolin-containing medium to label DNA replicated as cells entered S phase. Nuclear DNA was partially digested with Sau 3AI, and hybrid density DNA was separated in CsCl gradients. The purified early-replicating DNA was cloned into sCos1 cosmid vector. Clones were transferred individually into the wells of 96 microtiter plates (9,216 potential clones). Vigorous bacterial growth was detected in 8,742 of those wells. High-density colony hybridization filters (1, 536 clones/filter) were prepared from a set of replicas of the original plates. Bacteria remaining in the wells of replica plates were combined, mixed with freezing medium, and stored at -80 degrees C. These pooled stocks were analyzed by polymerase chain reaction to determine the presence of specific sequences in the library. Hybridization of high-density filters was used to identify the clones of interest, which were retrieved from the frozen cultures in the 96-well plates. In testing the library for the presence of 14 known early-replicating genes, we found sequences at or near 5 of them: APRT, beta-actin, beta-tubulin, c-myc, and HPRT. This library is a valuable resource for the isolation and analysis of certain DNA sequences replicated at the beginning of S phase, including potential origins of bidirectional replication.
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PMID:Construction of a cosmid library of DNA replicated early in the S phase of normal human fibroblasts. 1086 48

Triple helix forming oligonucleotides (TFOs) that bind chromosomal targets in living cells may become tools for genome manipulation, including gene knockout, conversion, or recombination. However, triplex formation by DNA third strands, particularly those in the pyrimidine motif, requires nonphysiological pH and Mg(2+) concentration, and this limits their development as gene-targeting reagents. Recent advances in oligonucleotide chemistry promise to solve these problems. For this study TFOs containing 2'-O-methoxy (2'-OMe) and 2'-O-(2-aminoethyl) (2'-AE) ribose substitutions in varying proportion have been constructed. The TFOs were linked to psoralen and designed to target and mutagenize a site in the hamster HPRT gene. T(m) analyses showed that triplexes formed by these TFOs were more stable than the underlying duplex, regardless of 2'-OMe/2'-AE ratio. However, TFOs with 2'-AE residues were more stable in physiological pH than those with only 2'-OMe sugars, as a simple function of 2'-AE content. In contrast, gene knockout assays revealed a threshold requirement--TFOs with three or four 2'-AE residues were at least 10-fold more active than the TFO with two 2'-AE residues. The HPRT knockout frequencies with the most active TFOs were 300-400-fold above the background, whereas there was no activity against the APRT gene, a monitor of nonspecific mutagenesis.
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PMID:Minimum number of 2'-O-(2-aminoethyl) residues required for gene knockout activity by triple helix forming oligonucleotides. 1205 3

Despite substantial progress in understanding the mechanism by which expanded CTG/CAG trinucleotide repeats cause neurodegenerative diseases, little is known about the basis for repeat instability itself. By taking advantage of a novel phenomenon, we have developed a selectable assay to detect contractions of CTG/CAG triplets. When inserted into an intron in the APRT gene or the HPRT minigene, long tracts of CTG/CAG repeats (more than about 33 repeat units) are efficiently incorporated into mRNA as a new exon, thereby rendering the encoded protein nonfunctional, whereas short repeat tracts do not affect the phenotype. Therefore, contractions of long repeats can be monitored in large cell populations, by selecting for HPRT(+) or APRT(+) clones. Using this selectable system, we determined the frequency of spontaneous contractions and showed that treatments with DNA-damaging agents stimulate repeat contractions. The selectable system that we have developed provides a versatile tool for the analysis of CTG/CAG repeat instability in mammalian cells. We also discuss how the effect of long CTG/CAG repeat tracts on splicing may contribute to the progression of polyglutamine diseases.
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PMID:Selectable system for monitoring the instability of CTG/CAG triplet repeats in mammalian cells. 1280 91

A metabolomic analysis of plasma amino acids and acylcarnitines was applied to four disorders of nucleotide metabolism. Multivariate analysis gave score plots that show segregation of hypoxanthine phosphoribosyltransferase and adenine phosphoribosyltransferase deficient plasma from controls with equivocal results for adenosine deaminase and dihydropyrimidine dehydrogenase deficiencies. Loadings plots revealed the principal metabolites responsible for the discrimination between these classes. There were increases for HPRT in C4-, C6-, and C3-DC (malonyl)-carnitines, and decreased serine. For APRT there were increases in C4- to C10- and C3-DC to C6-DC-carnitines, urea, 1-methylhistidine, 3-methylhistidine, and decreased tryptophan. For ADA deficiency there were increases in C4- and C6-carnitines, taurine, and isoleucine.
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PMID:Application of metabolomic principles to disorders of nucleotide metabolism reveals new metabolic perturbations. 1860 May 20


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