Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.3.5 (5'-nucleotidase)
3,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glycerate 2,3-bisphosphate, a potent stimulator of the cytosolic 5'-nucleotidase which preferentially hydrolyzes IMP and GMP in human erythrocytes (Bontemps et al., 1988, Biochem. J. 250, 687-696), also stimulates the dephosphorylation of IMP in cytosol fractions of rat heart, liver, brain, kidney, spleen and erythrocytes, and of human polymorphonuclear leucocytes, mixed peripheral blood lymphocytes, platelets and fibroblasts. Depending on the cell type, stimulation by 5 mM glycerate 2,3-bisphosphate varied from 1.5- to 12-fold. Where investigated, glycerate 2,3-bisphosphate had an approx. 5-fold higher affinity for the enzyme than its other stimulator, ATP. These observations provide a useful tool to distinguish IMP-GMP 5'-nucleotidase from other 5'-nucleotidases, and suggest a common origin of the cytosolic IMP-GMP 5'-nucleotidase in various tissues.
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PMID:Stimulation by glycerate 2,3-bisphosphate: a common property of cytosolic IMP-GMP 5'-nucleotidase in rat and human tissues. 254 5

2',3'-Dideoxyinosine (ddlno) is a potent and selective inhibitor of human immunodeficiency virus in human lymphoid cells and monocytes/macrophages. Earlier studies [J. Biol. Chem. 263:15354 (1988)] showed that anabolism of ddlno in human lymphoid cells is mediated via an initial step of phosphorylation and subsequent amination to dideoxy-AMP via adenylosuccinate synthetase/lyase. Evidence was obtained that neither adenosine kinase nor deoxycytidine kinase is involved in the phosphorylation of this compound in human lymphoid cells. We now find that, in the presence of MgCl2, KCl, and inosine-5'-monophosphate as phosphate donor, purified cytosolic 5'-nucleotidase catalyzed the phosphorylation of ddlno. Although not phosphate donors, ATP, diadenosine tetraphosphate, and glycerate-2,3-bisphosphate stimulate this phosphorylation by the nucleotidase 4-5-fold. In addition to ddlno, the antiviral nucleoside analogs 2',3'-dideoxyguanosine and carbovir were substrates for this enzyme. The relative phosphorylation of these compounds varied with the concentration of the phosphate donor IMP. Approximate Km values of the nucleotidase for inosine, ddlno, dideoxyguanosine, and carbovir were, respectively, 3.4, 0.5, 0.9, and 1.7 mM. Although the substrate activity of dideoxynucleosides is inefficient, it appears likely that this nucleotidase is responsible for the metabolism of these compounds to their active nucleotides, yielding antiviral activity in human lymphoid cells.
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PMID:Phosphorylation of 2',3'-dideoxyinosine by cytosolic 5'-nucleotidase of human lymphoid cells. 254 85

Changes in 5'-nucleotidase activity were calculated on the basis of alterations in ATP, ADP, phosphocreatine, Pi, Mg2+, IMP and AMP, determined by using 31P n.m.r. spectroscopy and h.p.l.c., during isoprenaline infusion, graded hypoxia and graded underperfusion in isolated rat heart. Calculated activity changes were compared with the total efflux of purines (adenosine + inosine + hypoxanthine) in order to assess the involvement of various 5'-nucleotidases in formation of adenosine. Purine efflux exhibited an exponential relation with cytosolic [AMP] during isoprenaline infusion and hypoxia (r = 0.92 and 0.95 respectively), supporting allosteric activation of 5'-nucleotidase under these conditions. Purine efflux displayed a linear relation with cytosolic [AMP] during graded ischaemia (r = 0.96), supporting substrate regulation in the ischaemic heart. The calculated activities of membrane-bound ecto-5'-nucleotidase were similar to the observed relations between purine efflux and cytosolic [AMP] in all hearts. The calculated activities of the ATP-activated cytosolic and lysosomal enzymes and of the ATP-inhibited cytosolic 5'-nucleotidase could not explain the observed release of purines under the conditions examined. These results indicate that the kinetic characteristics of the membrane-bound ecto-enzyme are consistent with an important role in the formation of extracellular adenosine, whereas the characteristics of the other 5'-nucleotidases are inconsistent with roles in adenosine formation under the conditions of the present study.
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PMID:5'-Nucleotidase activity and adenosine formation in stimulated, hypoxic and underperfused rat heart. 254 75

1. The partially purified IMP-specific cytosolic 5'-nucleotidases from rat liver, polymorphonuclear leucocytes and heart were inhibited by 50% by 2-6 mM-5'-deoxy-5'-isobutylthioadenosine (IBTA) or 7-10 mM-5'-deoxy-5'-isobutylthioinosine (IBTI). IBTA and IBTI inhibited the rat liver and polymorphonuclear-leucocyte enzymes non-competitively. IBTA, but not IBTI, also inhibited the ecto-5'-nucleotidase of polymorphonuclear leucocytes. IBTI was, by contrast, a more potent inhibitor than IBTA of the AMP-specific soluble 5'-nucleotidase from pigeon heart. 2. During 2-deoxyglucose-induced ATP-catabolism in rat polymorphonuclear leucocytes, adenosine formation was inhibited by approx. 80% by 3 mM-IBTA and by approx. 70% by 7 mM-IBTI. 3. The results show that 5'-modified nucleosides are inhibitors of cytosolic 5'-nucleotidases and that they penetrate to inhibit their target enzymes in intact cells. Such inhibitors may be useful to clarify the mechanisms of adenosine formation and to prevent mononucleotide hydrolysis during ATP breakdown.
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PMID:Inhibition of IMP-specific cytosolic 5'-nucleotidase and adenosine formation in rat polymorphonuclear leucocytes by 5'-deoxy-5'-isobutylthio derivatives of adenosine and inosine. 255 83

Two kinetically distinct purine 5'-phosphomono-esterase activities were isolated from soluble fractions of human placenta, cultured human T- and B-lymphoblasts and rat liver using AMP-sepharose chromatography. We have defined these activities as "high Km" and "low Km" 5'-nucleotidase. The relative content of "high Km" and "low Km" activities in the tissues studied ranged from 2 to 264. The optimum pH of "low Km" 5'-nucleotidases ranged from 7.4 to 9.0, Km for AMP from 7 to 15 uM and for IMP from 10 to 26 uM. ATP and ADP were inhibitors of "low Km" enzymes with the apparent Ki values of 55 to 20 uM and 8 to 20 uM for ATP and ADP, respectively. "High Km" 5'-nucleotidases had an optimum pH at 6.5, Km for IMP of 0.3 to 0.5 mM and Km for AMP of 1.0 to 9.4 mM. "High Km" enzymes were activated by ATP with A0.5 values, of 1.7 to 2.3 mM at 100 microM IMP. The data indicate that soluble "low Km" and "high Km" 5'-nucleotidases coexist in mammalian cells and fulfill different functions. These observations suggest a complex system for the regulation of AMP and IMP dephosphorylation.
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PMID:Evidence for "low Km" and "high Km" soluble 5'-nucleotidases in human tissues and rat liver. 255 32

The flux rates through the metabolic pathways affecting the maintenance of GuRN pool in intact human RBC were studied. Normal RBC, incubated in KRBB, exhibited a markedly higher accumulation in nucleotides of Gu than of Hx. Addition of 8-AGuo, a potent inhibitor of PNP, resulted in a marked increase in the accumulation of label in the nucleosides, in Ino following incubation with Hx, and in Guo following incubation with Gu, indicating a very high rate of IMP and GMP degradation to bases through their respective nucleosides. Most of the degradation of GMP is by dephosphorylation to Guo, rather than through reductive deamination to IMP. The ultimate fate of IMP in RBC is its degradation to Ino and consequently to Hx. The contribution of AdRN or of IMP to the GuRN pool is negligible. The results indicate that concerning IMP and GMP, human RBC contain very active futile cycles, nucleotide----nucleoside----base----nucleotide, catalyzed by 5'-nucleotidase, PNP, and HGPRT. The operation of the complete cycles is essential for the maintenance of GuRN and the IMP pool size. These results may explain the finding of reduced GTP content in RBC from patients with an inborn deficiency of PNP or of HGPRT.
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PMID:Guanine ribonucleotide metabolism in human red blood cells: evidence for a high rate of GMP dephosphorylation. 256 18

Residual 5'-nucleotidase activities in hemolysates from nine subjects with severe hereditary deficiency of pyrimidine nucleotidase (PyrNase) were compared to those in normal and reticulocyte-rich controls. Dephosphorylation rates of 12 potential ribo- and deoxyribomononucleotide substrates were measured as a function of pH. Data confirmed the existence of at least two isozymes of 5'-nucleotidase, PyrNase, and 2'-deoxy-5'-ribonucleotide phosphohydrolase (dNase) distinguishable by differences in maximal velocities, substrate preferences and restrictions, and pH optima. PyrNase was confirmed to be active principally with pyrimidine substrates (UMP = dCMP greater than CMP much greater than dTMP greater than dUMP) at a pH optimum of 7.5 +/- 0.1. dNase activity occurred with both purine and pyrimidine substrates and was maximal with deoxy analogs (dIMP much greater than dUMP greater than dGMP greater than dTMP = dAMP much greater than dCMP) at a pH optimum of 6.2, but slight cross-reactivity occurred with some nondeoxy substrates (IMP greater than GMP greater than UMP = XMP greater than CMP). PyrNase and dNase may be complementary systems that serve physiologically to clear the cytosol of RNA and DNA degradation products during maturation of erythroid elements by conversion of nucleotide monophosphates to diffusible nucleosides.
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PMID:Substrate specificity and pH sensitivity of deoxyribonucleotidase and pyrimidine nucleotidase activities in human hemolysates. 282 57

The pathways of AMP degradation and the metabolic fate of adenosine were studied in cultured myotubes under physiological conditions and during artificially induced enhanced degradation of ATP. The metabolic pathways were gauged by tracing the flow of radioactivity from ATP, prelabelled by incubation of the cultures with [14C]adenine, into the various purine derivatives. The fractional flow from AMP to inosine through adenosine was estimated by the use of the adenosine deaminase (EC 3.5.4.4) inhibitors, coformycin and 2'-deoxycoformycin. The activities of the enzymes involved with AMP and adenosine metabolism were determined in cell extracts. The results demonstrate that under physiological conditions, there is a small but significant flow of label from ATP to diffusible bases and nucleosides, most of which are effluxed to the incubation medium. This catabolic flow is mediated almost exclusively by the activity of AMP deaminase (EC 3.5.4.6), rather than by AMP 5'-nucleotidase (EC 3.1.3.5), reflecting the markedly higher Vmax/Km ratio for the deaminase. Enhancement of ATP degradation by inhibition of glycolysis or by combined inhibition of glycolysis and of electron transport resulted in a markedly greater flux of label from adenine nucleotides to nucleosides and bases, but did not alter significantly the ratio between AMP deamination and AMP dephosphorylation, which remained around 19:1. Combined inhibition of glycolysis and of electron transport resulted, in addition, in accumulation of label in IMP, reaching about 20% of total AMP degraded. In the intact myotubes at low adenosine concentration, the anabolic activity of adenosine kinase was at least 4.9-fold the catabolic activity of adenosine deaminase, in accord with the markedly higher Vmax/Km ratio of the kinase for adenosine. The results indicate the operation in the myotube cultures, under various rates of ATP degradation, of the AMP to IMP limb of the purine nucleotide cycle. On the other hand, the formation of purine bases and nucleosides, representing the majority of degraded ATP, indicates inefficient activity of the IMP to AMP limb of the cycle, as well as inefficient salvage of hypoxanthine under these conditions.
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PMID:Pathways of adenine nucleotide catabolism in primary rat muscle cultures. 282

A purine 5'-nucleotidase has been separated by DEAE-Trisacryl chromatography from other 5'-nucleotidase activities present in human haemolysates and purified approx. 30,000-fold by subsequent chromatography on Blue Sepharose. The enzyme has an Mr of around 250,000, displays hyperbolic substrate-saturation kinetics and hydrolyses preferentially IMP, GMP and their deoxy counterparts. It is much less active with AMP and dAMP. The purine 5'-nucleotidase is inhibited by Pi, and is strongly stimulated by ATP, dATP and GTP, and by glycerate 2,3-bisphosphate. Stimulators decrease Km and increase Vmax. Glycerate 2,3-bisphosphate is the most potent stimulator of the enzyme and, under physiological conditions, over-rides the influence of the other effectors. Glycerate 2,3-bisphosphate also influences the binding of the enzyme to DEAE-Trisacryl, as evidenced by the different elution profile obtained with fresh as compared with outdated blood. It is concluded that the glycerate 2,3-bisphosphate-stimulated purine 5'-nucleotidase is responsible for the dephosphorylation of IMP and GMP, but not of AMP, in human erythrocytes.
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PMID:5'-Nucleotidase activities in human erythrocytes. Identification of a purine 5'-nucleotidase stimulated by ATP and glycerate 2,3-bisphosphate. 283 44

1. A 5'-nucleotidase with a strong preference for AMP over IMP was characterized in homogenates and subcellular fractions of pigeon heart by using concentrations of ATP, ADP and AMP which mimicked those present in the ischaemic tissue. 2. The AMP-5'-nucleotidase had a neutral pH optimum and an apparent Km in the range 4.6-5.2 mM. It was stimulated by ATP plus ADP, and was inhibited by other nucleoside monophosphates, Pi and p-nitrophenyl phosphate, but not by ribose 5-phosphate or beta-glycerophosphate. The enzyme was not inhibited by [alpha beta-methylene] ADP or by 5'-deoxy-5'-isobutylthioadenosine, an inhibitor of the previously purified IMP-preferring cytosolic 5'-nucleotidase. 3. Subcellular-fractionation studies indicated that the enzyme has access to cytosolic AMP, although it may be associated by weak ionic interactions with an organelle present in the low-speed particulate fraction. 4. A 5'-nucleotidase was detected under similar conditions in homogenates of rat heart. 5. The activity of the pigeon heart AMP-5'-nucleotidase was sufficient to account for previously measured rates of ischaemia-induced adenosine formation. The similar activity in rat heart could, however, account for only part of ischaemia-induced adenosine formation in this tissue.
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PMID:The pigeon heart 5'-nucleotidase responsible for ischaemia-induced adenosine formation. 284 63


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