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 methodology is presented for systemic analysis of purine enzymes in small lymphocyte subfractions. For the determination of 7 different enzymes of purine metabolism *hypoxanthine-guanine phosphoribosyltransferase (HG-PRT), adenine phosphoribosyltransferase (A-PRT), adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), adenosine kinase (AK), 5'-nucleotidase (5'N), and AMP-deaminase) less than 200,000 peripheral blood lymphocytes are needed. 1000-6000 lyophilised lymphocytes are incubated in micro-incubation vessels (3 microliter) with radioactive substrates for 15-180 min. Separation of substrates and products is achieved by thin-layer chromatography on PEI-cellulose. Addition of BSA to the incubation mixtures results in higher specific enzyme activities and narrower ranges of mean values of a control group.
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PMID:Enzymes of purine nucleotide metabolism in human lymphocytes. 625 89

A mathematical model of energy metabolism of human red cells is presented, which includes besides the glycolytic reactions the adenine nucleotide metabolism. The model is based on the network of chemical reactions, the thermodynamic equilibrium constants of fast reversible reactions and on the kinetic equations for irreversible enzyme reactions. The model consists of a system of 16 differential equations and allows the mathematical evaluation of metabolic levels in the steady state of energy metabolism corresponding to the in vivo state erythrocytes with the kinetic data for the enzymes derived from in vitro experiments. The dependence of the levels of metabolites in the steady state on the activity of some enzymes is analysed to characterize the regulatory properties of the system. The comparison of the steady state levels of the model with experimental data makes it possible to estimate values of some controversial enzyme parameters. Estimates of the kinetic parameters of the following intracellular processes are presented: 1) rate constant of AMP-phosphatase, 2) maximum rate of adenylate deaminase, 3) activity of adenine phosphoribosylpyrophosphate transferase and 4) adenosine transport through the cell membrane. The simulation of the preparatory phase before incubation of erythrocytes indicates, that the model also permits to compute the time course of changes of levels of metabolites. To solve the initial problem the stiff differential equation system is integrated numerically by an efficient program without the application of the quasi-steady-state approximation.
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PMID:[Mathematical modelling of glycolysis and adenine nucleotide metabolism of human erythrocytes. I. Reaction-kinetic statements, analysis of in vivo state and determination of starting conditions for in vitro experiments]. 628 49

Sealed and unsealed plasma membrane vesicles were prepared from human erythrocytes and lymphocytes. Phosphoribosylpyrophosphate synthetase (PRibPP synthetase), hypoxanthine phosphoribosyltransferase (HPRTase), and adenine phosphoribosyltransferase (APRTase) activities are detectable on both inside-out and right-side-out sealed vesicles. Ghost preparations were about 0.2%, 1%, and 1.2% of the total erythrocyte and 0.5%, 5.3%, and 9.7% of the lymphocyte APRTase, HPRTase, and PRibPP synthetase activities. The rapid decrease in these enzyme activities, upon further purification of the membranes, seemed to suggest that they might be loosely bound extrinsic proteins. Evidence confirming the localization of these enzymes on the cell surface was obtained by measuring production of [14C]AMP by intact cells in medium containing [14C]adenine, ribose 5-phosphate, and Mg2+ATP. The formation of AMP was linear with time and number of cells present. Magnesium and phosphate exerted different effects on the production of extracellular AMP than on intracellular, which involves transport as well as phosphoribosylation. Cytosoluble and membrane-bound APRTase and PRibPP synthetase exhibited different catalytic properties and sensitivities to effectors. Membranes of erythrocytes of HPRTase-deficient patients contain little or no HPRTase activity when assayed in the absence of Triton. Reisolation of these membranes from admixture with normal hemolysates did not result in any bound activity; thus, the membrane-bound activity is not an artifact of the isolation procedure. Lysis with Triton released activity equal to about half that of control membranes. This is further evidence that the enzyme is firmly bound to the membrane.
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PMID:Membrane-associated purine metabolizing enzyme activities of human peripheral blood cells. 629 41

An enzyme capable of degrading 5'-methylthioadenosine to adenine was found in the human erythrocyte. A rapid assay for this enzyme, 5'-methylthioadenosine phosphorylase, was developed using high pressure liquid chromatography. The specific activity in 24 normal subjects was 8.9 +/- 2.0 nmol . mg-1 Hb . h-1. Levels within this range were also found in erythrocyte lysates from gouty subjects and patients with a variety of inborn errors of purine metabolism, including patients with a complete deficiency of the adenine salvage enzyme--adenine phosphoribosyltransferase. Erythrocyte lysates from the latter however, were unable to convert the adenine produced to AMP in a linked assay system, in contrast to controls and other patients. These results support the suggestion that adenine, which is excreted in quantity by patients with adenine phosphoribosyltransferase deficiency is derived endogenously from 5'-methylthioadenosine as a by-product of polyamine biosynthesis.
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PMID:Methylthioadenosine phosphorylase activity in human erythrocytes. 640 3

Adenosine deaminase (ADA), 5'nucleotidase (5'NT), ecto-5'NT, purine nucleoside phosphorylase (PNP), hypoxanthine-guanine phosphoribosyltransferase (HGPRT), adenine phosphoribosyltransferase (APRT), adenosine kinase (AK), AMP-deaminase (AMPD) and adenylate kinase (AdKin) activities were assayed in peripheral blood lymphoid cells from 20 patients with B-cell type chronic lymphocytic leukemia (CLL). Significantly decreased mean activities of ADA, 5'NT, ecto-5'NT, PNP and AMPD were observed when comparing B-CLL lymphoid cells with control peripheral blood lymphocytes (PBL). AK and AdKin activities however, were found to be higher in B-CLL. Relatively wide ranges of ADA and 5'NT activity were observed. In patients with paraproteinaemia, 5'NT activity was found to be relatively high and in the range of the activities in normal PBL. ADA activity seemed to be slightly higher in patients without paraproteinaemia. No correlation could be found between the enzyme activities and the number of cells rosetting with sheep erythrocytes or bearing surface immunoglobulin (sIg). A relationship was suggested between 5'NT activity and Ig production.
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PMID:Enzymological studies in chronic lymphocytic leukemia. 640 72

A study was made of the activity of adenine-phosphoribosyltransferase (EC 2.4.2.7), which catalizes the biosynthesis of AMP from adenine and 5-phospho-alpha-D-riboso-1-diphosphate, in extracts from thymus and liver during 24 h following irradiation of mice in a dose of 245.1 mC/kg (dose-rate of 9.16 X 10(-4)-9.0 X 10(-4) A/kg). Adenine-phosphoribosyltransferase activity of liver remains normal during the entire period of observation. In thymus extracts, the activity of the enzyme decreases down to 70-80% of the control level 3 h after irradiation, it is normalized after 6 h and increases up to 150-160% of the control level by the end of the first day of radiation sickness.
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PMID:[Postradiation disorders in the adenine-phosphoribosyltransferase pathway of AMP biosynthesis]. 673 37

When added to medium containing coformycin (2 microM or above), adenine is lethal to Chinese hamster fibroblasts at the concentration inhibiting de novo purine biosynthesis (Debatisse and Buttin, '77b). Rescue by hypoxanthine suggested that cells die of IMP starvation when the analog can turn off deamination of both adenosine and adenylate. As predicted from this hypothesis, two classes of variants resistant to the mixture of coformycin + adenine have been isolated: Class 1 variants have altered control of de novo IMP biosynthesis; they fall into two subclasses on the basis of their resistance to adenosine. Class 2 variants have a 6-10-fold increased level of AMP-deaminase (E.C.: 3.5.4.6); their growth in the selective medium is temperature-dependent, a property accounted for by the observation that cell growth in the presence of coformycin imposes a gradual thermodependent decay of specific AMP-deaminase activity in both wild-type and variant lines. This control by coformycin of AMP-deaminase activity is unaltered in mutants deficient in the four activities of adenosine-kinase. APRT, HGPRT and deoxycytidine-kinase. Most of the resistant variants are unstable and exhibit either increased or reduced resistance, depending on prolonged growth in selective or normal medium.
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PMID:The potentiation of adenine toxicity to Chinese hamster cells by coformycin: suppression in mutants with altered regulation of purine biosynthesis or increased adenylate-deaminase activity. 720 4

Tissue adenine nucleotides are depleted during cerebral ischemia, impeding recovery after reperfusion. Although prior studies have attempted to prevent the initial loss of adenylates, the present study tests the hypothesis that stimulating synthesis of adenine nucleotides, through either adenosine kinase or adenine phosphoribosyltransferase, would result in significant cerebroprotection. To study the effects on neurons and glia directly while avoiding the influence of the cerebral vasculature, hippocampal brain slices were used for the model of transient ischemia with reperfusion. The standard brain slice insult of brief exposure to anoxia with aglycemia was modified based on studies which showed that a 30-minute exposure to air with 1 mmol/L glucose produced a stable, moderate reduction in ATP during the insult and that, 2 hours after return to normal conditions, there was moderate depletion of tissue adenine nucleotides and histologic injury. Treatments with 1 mmol/L adenosine, AMP, or adenine were equivalent in partially restoring adenine nucleotides. Despite this, only adenosine afforded histologic protection, suggesting a protective role for adenosine receptors. There also was evidence for metabolic cycling among adenine nucleotides, nucleosides, and purines. Adenosine may exert direct cerebroprotective effects on neural tissue as well as indirect effects through the cerebral vasculature.
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PMID:Restoring adenine nucleotides in a brain slice model of cerebral reperfusion. 962 92

In humans, adenine phosphoribosyltransferase (APRT, EC 2.4.2.7) deficiency can manifest as nephrolithiasis, interstitial nephritis, and chronic renal failure. APRT catalyzes synthesis of AMP from adenine and 5-phosphoribosyl-1-pyrophosphate. In the absence of APRT, 2,8-dihydroxyadenine (DHA) is produced from adenine by xanthine dehydrogenase (XDH) and can precipitate in the renal interstitium, resulting in kidney disease. Treatment with allopurinol controls formation of DHA stones by inhibiting XDH activity. Kidney disease in APRT-deficient mice resembles that seen in humans. By age 12 wk, APRT-deficient male mice are, on average, mildly anemic and smaller than normal males. They have extensive renal interstitial damage (assessed by image analysis) and elevated blood urea nitrogen (BUN), and their creatinine clearance rates, which measure excretion of infused creatinine as an estimate of glomerular filtration rate (GFR), are about half that of wild-type males. APRT-deficient males treated with allopurinol in the drinking water had normal BUN and less extensive visible renal damage, but creatinine clearance remained low. Throughout their lifespans, homozygous null female mice manifested significantly less renal damage than homozygous null males of the same age. APRT-deficient females showed no significant impairment of GFR at age 12 wk. Consequences of APRT deficiency in male mice are more pronounced than in females, possibly due to differences in rates of adenine or DHA synthesis or to sex-determined responses of the kidneys.
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PMID:Chronic renal failure in a mouse model of human adenine phosphoribosyltransferase deficiency. 968 17

The hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRTase) from Tritrichomonas foetus has been proven to be a target for potential anti-tritrichomonial chemotherapy. Using a structure-based approach, the base-binding region of the active site of this enzyme, which confers unique purine base specificity, was characterized using site-directed mutagenesis. Determining the roles of different active-site residues in purine specificity would form the basis for designing specific inhibitors toward the parasitic enzyme. A D163N mutant converts the HGXPRTase into a HGPRTase, which no longer recognizes xanthine as a substrate, whereas specificities toward guanine and hypoxanthine are unaffected. Apparently, the side-chain carboxyl of Asp163 forms a hydrogen bond through a water molecule with the C2-carbonyl of xanthine, which constitutes the critical force enabling the enzyme to recognize xanthine as a substrate. Mutations of Arg155, which orients and stacks the neighboring Tyr156 onto the bound purine base by forming a salt bridge between itself and Glu11, result in drastic increases in the Kms for GMP and XMP (but not IMP). This change leads to increased kcats for the forward reactions with guanine and xanthine as substrates without affecting the conversion of hypoxanthine to IMP. Thus, the apparent dislocation of Tyr156, resulted from mutations of Arg155, bring little effect on the hydrophobic interactions between Tyr156 and the purine ring. But the forces involved in recognizing the exocyclic C2-substituents of the purine ring, which involve the Tyr156 hydroxyl, Ile157 backbone carbonyl, and Asp163 side-chain carboxyl, may be weakened by the shifted conformation of the peptide backbone resulted from loss of the Glu11-Arg155 salt bridge. The conserved Lys134 was proven to be the primary determinant in conferring the specificity of the enzyme toward 6-oxopurines. By substituting the lysine residue for a serine, which can potentially hydrogen bond to either an amino or an oxo-group, we have successfully augmented the purine specificity of the enzyme. The K134S mutant recognizes adenine in addition to hypoxanthine, guanine, and xanthine as its substrates. Adenine and hypoxanthine are equivalent substrates for the mutant enzyme with similar Kms of 34.6 and 38.0 microM, respectively. The catalysis of an adenine phosphoribosyltransferase reaction by this mutant enzyme was further demonstrated by the competitive inhibition of AMP with an estimated Kis of 25.4 microM against alpha-D-5-phosphoribosyl-pyrophosphate (PRPP) in converting hypoxanthine to IMP. We have thus succeeded in using site-directed mutagenesis to convert T. foetusHGXPRTase into either a HGPRTase or a genuine AHGXPRTase.
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PMID:Altering the purine specificity of hypoxanthine-guanine-xanthine phosphoribosyltransferase from Tritrichomonas foetus by structure-based point mutations in the enzyme protein. 984 28


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