Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.8 (polynucleotide phosphorylase)
 723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The inherited deficiency of purine-nucleoside phosphorylase (PNPase; purine-nucleoside:orthophosphate ribosyltransferase, EC 2.4.2.1) in humans is associated with a severe deficiency of the T lymphocytes of the immune system. Because of the unsatisfactory nature of previously described model systems, we have selected, cloned, and characterized a mutant mouse T cell lymphoma (S49) completely deficient in PNPase. Of the four substrates of PNPase, only deoxyguanosine at low concentrations is toxic to the PNPase-deficient (NSU-1) cells. In order to delineate the biochemical processes necessary for the sensitivity of the NSU-1 cells to deoxyguanosine, we have isolated a series of secondary mutants resistant to deoxyguanosine from the PNPase-deficient line. One of these mutants is defective in its ability to transport deoxyguanosine into the cell. A second type of mutant cannot phosphorylate the deoxyguanosine and is totally deficient in deoxycytidine kinase activity. A third type of mutant (NSU-1-dGuo-L) can both transport and phosphorylate deoxyguanosine and accumulates dGTP. However, unlike its parent, NSU-1-dGuo-L does not become depleted of dCTP and TTP when exposed to exogenous deoxyguanosine. This observation is accounted for by the fact that the reduction of CDP to dCDP by the ribonucleotide reductase (ribonucleoside-diphosphate reductase, 2'-deoxyribonucleoside-diphosphate:oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1) of NSU-1-dGuo-L cells is not normally sensitive to feedback inhibition by dGTP.Thus, in order to exert its toxicity deoxyguanosine must be transported into the cell, be phosphorylated by deoxycytidine kinase, and be accumulated as dGTP. By inhibiting ribonucleotide reductase, dGTP depletes the cell of dCTP and to some extent TTP, thus preventing the synthesis of DNA, a process necessary for any proliferation-dependent function of T cells.
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PMID:Isolation and characterization of purine-nucleoside phosphorylase-deficient T-lymphoma cells and secondary mutants with altered ribonucleotide reductase: genetic model for immunodeficiency disease. 10 75

The kinetic model of carbohydrate metabolism has been expanded to include: (a) the accumulation of alpha and beta-cellulose, insoluble cell-wall glycogen and mucopolysaccharide; (b) the role of RNA turnover as a source of carbon for end-product synthesis and as a buffer regulating the level of uridine nucleotides in this metabolic network; and (c) the role of purine-nucleoside phosphorylase, 5'-AMP nucleotidase, nucleosidediphosphate kinase and polynucleotide phosphorylase. One of many predictions based on this model is that cells differentiating in the presence of glucose will produce sorocarps with an abnormally high trehalose to cellulose ratio. External perturbation of either the model or of developing cells by glucose increases the levels of sorocarp trehalose and glycogen, 5-fold and 6-fold respectively. Evaluation of the experimental data and the simulation analyses have allowed several predictions to be made concerning the compartmentation of metabolites and the permeability of cells to glucose during differentiation.
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PMID:Fourth expansion and glucose perturbation of the Dictyostelium kinetic model. 55 94

We have studied the kinetics of guanine incorporation into DNA in mouse T-lymphoma (S-49) mutant cells [PNPase (purine-nucleoside phosphorylase)- and HGPRTase (hypoxanthine: guanine phosphoribosyltransferase)-deficient] that are incapable of converting dGuo (deoxyguanosine) to Gua (guanine) ribonucleotides. Of the two possible pathways for an exogenous guanine source to reach DNA, firstly: dGuo----dGMP----dGDP----dGTP and secondly: Gua----GMP----GDP----dGDP----dGTP only the second pathway was found to be functional in providing guanine for DNA replication, although deoxyguanosine readily produced toxic cellular dGTP levels via the first pathway. The functional guanine-nucleotide-precursor pools for DNA are rather small; further, the depletion of the small GMP pool, but not that of GDP, GTP and dGTP, correlated well with the inhibition of DNA synthesis by mycophenolic acid, an IMP dehydrogenase inhibitor. These results support the hypothesis that guanine-nucleotide incorporation into DNA is highly compartmentalized and that a small functional guanine-nucleotide pool, e.g., the GMP pool, may serve a crucial role in limiting the availability of DNA precursor substrate.
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PMID:Compartmentation of guanine nucleotide precursors for DNA synthesis. 242 29

Two types of mutants lacking the second purine nucleoside phosphorylase (PNPase 2) activity were isolated using the Escherichia coli K-12 pndR strains with constitutive or inosine-inducible synthesis of the PNPase 2. The mutations of the first type are recessive to the pndR+ allele on the F' episome. They are closely linked to the original pndR+ mutations and therefore affect the pndR gene encoding the activator protein. The mutations of the second type affect the PNPase 2 structural gene (pndA) and are recessive to the pndA+ allele on the F' episome. The nupC-pndR-pndA-ptsH-cysA gene order was established by means of four- and five-factorial transductional crosses.
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PMID:[Genetic analysis of Escherichia coli K-12 mutants defective for the structural and regulatory genes for second purine nucleoside phosphorylase]. 309 87

Restoration of the ability to catabolise the purine nucleosides in phenotypic revertants of Escherichia coli K-12 mutants defective in deoD encoded purine nucleoside phosphorylase (PNPase 1) is the result of regulatory pndR mutations for synthesis of a second purine nucleoside phosphorylase (PNPase 2). In pndR+ strains synthesis of PNPase 2 is induced by xanthosine; in pndR mutants catabolising all purine nucleosides synthesis of this enzyme is constitutive; in other pndR mutants only catabolising some of purine nucleosides, this catabolisible nucleosides, namely, deoxyinosine, deoxyadenosine as well as, in some cases, inosine and adenosine, act as inducers of PNPase 2 synthesis. In some pndR mutants with inducible PNPase 2, xanthosine is a stronger inducer, in others it is weaker, in comparison with pndR+ strains. In bacterial cells PNPase 2 catalyses the phosphorolytic cleavage of adenosine, inosine, deoxyinosine, guanosine, deoxyguanosine and xanthosine, though in crude extracts adenosine and deoxyadenosine phosphorylase activities of the enzyme are not expressed.
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PMID:[Regulatory mutants for the synthesis of a 2d purine nucleoside phosphorylase in Escherichia coli K-12. I. Synthesis inducers and the substrate specificity of purine nucleoside phosphorylase in pndR mutants]. 643 6

The reversed-phase mode of high-performance liquid chromatography (HPLC) was used to assay purine nucleoside phosphorylase (PNPase E.C. 2.4.2.1) in human erythrocytes. The reaction conditions were optimized with respect to pH, concentration of enzyme, concentration of substrate and time. In this method, a sample of erythrocytes was incubated with substrate and necessary cofactors. After termination of the reaction, both the decrease in substrate and the increase in product were measured. HPLC is highly suitable for PNPase as both the forward and reverse reactions can be monitored. The complete separation of products from reactants allows the determination of any competing or side reactions.
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PMID:Optimized assay for purine nucleoside phosphorylase by reversed-phase high-performance liquid chromatography. 677 85

Remarkable activity of various enzymes involved in adenine nucleotide degradation has been revealed in the endothelium recently. Using the highly sensitive radiochromatographic methods, the activities of 5'-nucleotidase, EC: 3.1.3.5. (5'-Nase), adenine deaminase, EC: 3.5.4.4. (ADase), and purine nucleoside phosphorylase, EC: 2.4.2.5. (PN-Pase) were estimated in the endothelium from normal human aortas characterized by a regular arrangement of cells and in the endothelium from atherosclerotic aortas characterized by different size and often multinucleated cells. Activities of 5'-Nase and ADase in the endothelial cells of atherosclerotic aortas were significantly higher than activities in normal ones. However, the activity of PNPase was approximately on the same level in both aortas. The above findings indicate a shift in the activity of 5'-Nase and ADase, which might be a result of the atherosclerotic process as well as the aggregation of platelets.
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PMID:Activity of some adenine nucleotide degradation enzymes in human atherosclerotic aorta endothelium. 818 97

In the aging population, lower urinary tract (LUT) dysfunction is common and often leads to storage and voiding difficulties classified into overlapping symptom syndromes. Despite prevalence and consequences of these syndromes, LUT disorders continue to be undertreated simply because there are few therapeutic options. LUT function and structure were assessed in aged (>25 months) male and female Fischer 344 rats randomized to oral treatment with a purine nucleoside phosphorylase (PNPase inhibitor) 8-aminoguanine (8-AG) or vehicle for 6 weeks. The bladders of aged rats exhibited multiple abnormalities: tactile insensitivity, vascular remodeling, reduced collagen-fiber tortuosity, increased bladder stiffness, abnormal smooth muscle morphology, swelling of mitochondria, and increases in urodamaging purine metabolites. Treatment of aged rats with 8-AG restored all evaluated histological, ultrastructural, and physiological abnormalities toward that of a younger state. 8-AG is an effective treatment that ameliorates key age-related structural and physiologic bladder abnormalities. Because PNPase inhibition blocks metabolism of inosine to hypoxanthine and guanosine to guanine, likely uroprotective effects of 8-AG are mediated by increased bladder levels of uroprotective inosine and guanosine and reductions in urodamaging hypoxanthine and xanthine. These findings demonstrate that 8-AG has translational potential for treating age-associated LUT dysfunctions and resultant syndromes in humans.
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PMID:Purine nucleoside phosphorylase inhibition ameliorates age-associated lower urinary tract dysfunctions. 3291 Aug 5