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)

The liver is a primary target for both acute and chronic effects of ethanol. Because ethanol is known to alter the function of guanine nucleotide regulatory proteins (G-proteins), changes in hepatic G-proteins could contribute to the adverse effects of ethanol on liver function. Male Wistar rats were fed a liquid diet containing 36% of calories as ethanol for 4 weeks. Control rats were pair-fed or allowed free access to a diet that isocalorically substituted maltose dextrins for ethanol. Liver plasma membranes were isolated and separated into basolateral and canalicular fractions by sucrose-density gradients. Enrichment of marker enzymes (5'-nucleotidase for canalicular membranes and forskolin-stimulated adenylyl cyclase activity for basolateral membranes) was not affected by ethanol feeding. Quantity of G alpha s and G alpha i proteins in membrane fractions was determined by immunoblot. After ethanol feeding, immunoreactive G alpha s protein was increased in liver plasma membranes compared with pair-fed controls. G alpha i and G alpha s were present in both the basolateral and canalicular fractions of the plasma membrane in control and ethanol-fed rats. G alpha s quantity in the basolateral membrane was greater in ethanol-fed rats compared with controls, with no differences in G alpha s observed in canalicular membranes. The quantity of G alpha i did not change in response to ethanol feeding in any of the membrane fractions. Treatment of isolated plasma and basolateral membranes with 10 mumol/L 5'-guanylimidophosphate, a nonhydrolyzable guanosine triphosphate analogue that activates G-proteins, increased cAMP production to a greater extent in ethanol-fed rats compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Chronic ethanol feeding increases the quantity of G alpha s-protein in rat liver plasma membranes. 770 91

Primary hepatocytes were cultured on collagen gel in serum-free, alpha-modified Eagle's minimum essential medium containing 0.1 microM insulin, 0.1 microM dexamethasone, 10 mM pyruvate and supplements such as glucagon, epinephrine or growth hormone. The activities of alkaline phosphatase, 5'-nucleotidase and gamma-glutamyltransferase were assayed in cell extracts prepared from the cultures. All three enzyme activities were induced by glucagon, epinephrine or dibutyryl cAMP. The maximally effective concentration of glucagon was 5-10 nM for both alkaline phosphatase and 5'-nucleotidase and 100 nM for gamma-glutamyltransferase. Only alkaline phosphatase activity was suppressed by growth hormone, which caused marked suppression at about 1 microU (0.25 ng)/ml. Taurocholate also induced both alkaline phosphatase and gamma-glutamyltransferase activities at 1 mM.
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PMID:Hormonal regulations of alkaline phosphatase, 5'-nucleotidase and gamma-glutamyltransferase activities in adult rat hepatocytes cultured in serum-free medium on collagen gel. 809 10

It has been claimed recently that, in several cell types, ATP can induce a stimulation of cAMP production which is sensitive to methylxanthine inhibition and is not mediated by the ATP degradation product, adenosine. One explanation for these results would be direct activation of adenosine A2 receptors by ATP itself. We have therefore investigated whether adenine nucleotides are ligands of adenosine A2A receptors from bovine striatum. We show here that ATP, ADP, AMP and their phosphorothioates analogues (ATP gamma S, ADP beta S and AMP alpha S), at a 100 microM concentration, produced a 83-91% inhibition of the binding of [3H]CGS21680, an adenosine A2A receptor agonist, to striatum membranes. However, this action was inhibited by adenosine deaminase or by adenosine 5'-O-(alpha, beta-methylene)diphosphate (APCP), an inhibitor of 5'-nucleotidase-mediated AMP degradation. The effects of adenosine deaminase and APCP were dependent on their concentration. These results indicate that ATP, ADP and even AMP can exert an effect on the adenosine A2A receptors only through their breakdown into adenosine by ectonucleotidases.
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PMID:Evidence that ATP, ADP and AMP are not ligands of the striatal adenosine A2A receptors. 822 25

This study was done to determine glucagon's effect on protein biliary excretion in anesthetized, bile duct-cannulated guinea pigs. Glucagon (1.4 nmol.min-1.kg-1) induced choleresis and increased protein biliary concentration from 0.12 +/- 0.04 to 0.20 +/- 0.6 mg/ml and protein output from 22.8 +/- 3.8 to 54.5 +/- 16.1 micrograms.kg-1.min-1. Protein biliary excretion increased during the first 10 min of glucagon infusion and progressively declined thereafter. Biochemical analysis of biliary protein revealed that the increase could be accounted for primarily by an increase in the lysosomal enzymes acid phosphatase and beta-glucuronidase. Biliary excretion of the canalicular membrane enzymes 5'-nucleotidase and alkaline phosphatase only modestly increased, whereas that of [14C]sucrose, a marker of paracellular fluid transport, was unaffected. On the other hand, glucagon enhanced biliary entry of horseradish peroxidase in a fashion similar to that observed with total endogenous protein. These effects were mediated by the adenosine 3',5'-cyclic monophosphate (cAMP) system, since infusion of dibutyryl-cAMP at 0.5 mumol.kg-1.min-1 increased bile flow and biliary protein excretion in a time-dependent manner, as observed with glucagon. Glucagon's failure to sustain enhanced protein biliary output was not due to declining hepatic concentrations of cAMP or to depletion of hepatocellular lysosomal enzymes. These studies provide evidence that glucagon stimulates biliary excretion of protein in guinea pigs that can be accounted for by biliary discharge of enzyme originating from the canalicular membrane and, primarily, from the lysosomal compartment. Although the precise mechanism(s) underlying these effects remains to be elucidated, it is suggested that the increase in canalicular membrane enzyme excretion is due to glucagon's effect on exocytosis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Glucagon induces biliary protein excretion in guinea pigs. 838 43

Because A2 adenosine receptor activation stimulates adenylate cyclase and cyclic AMP induces 5'-nucleotidase expression in rat mesangial cells, we examined the effect of adenosine and its analogs on 5'-nucleotidase activity in these cells. A2 adenosine receptors were characterized using [3H]5'-N-ethylcarboxamidoadenosine (NECA) as a tracer. There was a single group of receptor sites with a KD value of 0.53 microM and a number of sites of 1,317 fmol/mg. [3H]NECA binding was inhibited preferentially by A2 adenosine analogs and antagonists. Similarly, the order of potency for cAMP stimulation was in favour of A2 adenosine analogs. Rat mesangial cells expressed surface 5'-nucleotidase activity. Exposure of cells for 48 h to adenosine analogs showed that at low concentrations A2 analogs stimulated 5'-nucleotidase activity. These results indicate that adenosine upregulates activity of 5'-nucleotidase, the enzyme responsible for its local formation, via A2 receptor stimulation and increase in cAMP production.
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PMID:Adenosine stimulates 5'-nucleotidase activity in rat mesangial cells via A2 receptors. 840 20

Adenosine is an important inhibitory neuromodulator in the cerebral cortex, yet it remains unclear how extracellular adenosine concentrations are regulated. Recently, it has been shown that beta-adrenergic receptor stimulation in rat cortical cultures causes the accumulation of extracellular adenosine derived by enzymatic hydrolysis from adenosine cyclic monophosphate (cAMP) transported into the extracellular space. In this study we show that vasoactive intestinal peptide (VIP), in addition to activating adenylyl cyclase and promoting the accumulation of intracellular cAMP in rat cortical cultures, also causes transport of cAMP and accumulation of extracellular adenosine. We further show that the extracellular accumulation of adenosine in response to VIP can be blocked by inhibition of cAMP transport, cyclic nucleotide phosphodiesterase activity, and 5'-nucleotidase, indicating that extracellular cAMP is the source of the adenosine. Cyclic AMP transport may be a general mechanism by which a variety of neuromodulators that act upon receptors coupled to adenylyl cyclase might regulate extracellular adenosine levels and thereby inhibitory tone in the cerebral cortex.
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PMID:Vasoactive intestinal peptide regulates extracellular adenosine levels in rat cortical cultures. 861 71

The human leukocyte surface Ag CD38 was recently identified as a nicotinamide adenine dinucleotide (NAD)(+)-glycohydrolase ecto-enzyme, degrading NAD into nicotinamide and ADP-ribose. We show here that expression of CD38 is increased in the Jurkat T cell line after treatment with agents that augment intracellular cAMP, with the permeant cAMP analogue dibutyryl-cAMP (db-cAMP), and also with PMA, which activates protein kinase C. Treatment of human PBL T cells with db-cAMP or submitogenic doses of PMA also increased CD38 expression. Two other nucleotide-hydrolyzing activities were induced on the T cell surface concomitantly with CD38: the human PC-1 molecule, a nucleotide phosphodiesterase/pyrophosphatase that produces AMP from NAD or ADP-ribose, and a nucleotidase that produces adenosine from AMP, but which may be distinct from the CD73 5'-nucleotidase. All three enzymes were up-regulated after stimulation of human peripheral blood T cells with PHA. The coordinated regulation of these ecto-enzymes suggested that, besides a possible signaling function, they may recycle extracellular NAD by degrading it to adenosine and nicotinamide, which can be taken up by cells. In support of this hypothesis, db-cAMP-treated Jurkat cells could degrade extracellular NAD for de novo synthesis of purines, while untreated cells could not. Activated lymphocytes are often located in tissues in which cell death is common. It is suggested that the coordinated expression of these enzymes may allow activated T cells to re-use NAD and nucleotides from dead cells.
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PMID:Coordinated regulation in human T cells of nucleotide-hydrolyzing ecto-enzymatic activities, including CD38 and PC-1. Possible role in the recycling of nicotinamide adenine dinucleotide metabolites. 875 17

Adenylate cyclase (AC) and 5'-nucleotidase (NT) activities were measured in the limbic (amygdala, hippocampus) and sensorimotor (cortex, striatum) structures of the brain in three groups of rats: untrained rats and rats which were good and poor learners in training to perform movements involving pushing against an obstruction. After training, AC activity decreased in all structures studied. Activity decreased in the cortex and striatum to a greater extent in good learners, and in the amygdala in poor learners. NT activity decreased in all brain structures apart from the striatum, to a greater extent in rats which were less able to learn to produce movements involving prolonged pushing. The striatum was the only structure in which increases in NT activity occurred, from the lowest initial level in the control group. 1.0 +/- 0.04 microgram P(i)/mg protein/min, to 1.3 +/- 0.1 micrograms P(i)/mg protein/min in poor learners and to 2.0 +/- 0.1 micrograms P(i)/mg protein/min in good learners. Interhemisphere asymmetries in AC activity in the cortex and hippocampus were seen, along with an interhemisphere difference in NT activity in the amygdala. Thus, the activity of enzymes involved in adenine and cAMP biosynthesis changed in different ways in the limbic and sensorimotor structures of the brain, depending on the ability of rats to learn. The increase in NT activity after training of rats, which was limited to the striatum, may reflect a special role for the purinergic system in these structures in mediating sensation-regulated movements.
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PMID:Activity of adenylate cyclase and 5'-nucleotidase in the sensorimotor and limbic structures of the brain in rats after manipulatory training. 912 32

There are multiple mechanisms by which adenine nucleotides can be released into the extracellular space in brain. Adenine nucleotides are converted extracellularly to adenosine, which then acts on adenosine receptors to elicit physiological responses, but the rate at which this conversion takes place is unknown. In the present experiments, adenine nucleotides were applied to individual hippocampal neurons, and the subsequent activation of a postsynaptic K+ conductance by adenosine A1 receptors was used to determine the rate of adenosine formation. None of the adenine nucleotides tested (cAMP, AMP, ADP, and ATP) activated A1 receptors directly at the concentrations tested (</=200 microM). AMP, ADP, and ATP were all rapidly converted to adenosine, with a T1/2 for ATP conversion to adenosine of approximately 200 msec, and the last step in this pathway (transformation of AMP to adenosine by 5'-nucleotidase) seems to be the rate-limiting step. As we have reported previously, cAMP is converted to adenosine as well, but on a much slower time scale than any of the other nucleotides tested. These experiments demonstrate that fast, localized release of AMP, ADP, or ATP can result in a transient activation of adenosine receptors but that this is unlikely to occur with cAMP. The existence of a highly active ecto-nucleotidase pathway in brain provides a mechanism for the rapid generation of adenosine after the release of adenine nucleotides into the extracellular space.
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PMID:Adenine nucleotides undergo rapid, quantitative conversion to adenosine in the extracellular space in rat hippocampus. 931 89

Few studies have examined tubular function after subtotal nephrectomy (Nx) and conservative treatments. The effects of 70% and 80% Nx (associated with dietary phosphate restriction in the latter case) on the apical brush border membrane (BBM) enzymes 5'-nucleotidase, gamma glutamyl-transferase and alkaline-phosphatase, and one BBM Na-phosphate cotransporter (NaPi-2) were studied in rats after a six week period. Changes in activity and mRNA abundance of the BBM enzymes and in NaPi-2 protein and mRNA abundance were compared with changes in the distal markers of Na,K-ATPase activity and epidermal growth factor (EGF) production. The activity, but not the mRNA of BBM enzymes, was moderately reduced by the 70% Nx. Both the mRNA and activity of gamma glutamyl-transferase and alkaline-phosphatase were decreased in the 80% Nx, and the NaPi-2 mRNA, protein and Na,K-ATPase activities were also reduced. These effects (except for 5'nucleotidase and Na,K-ATPase) were partly reversed by phosphate restriction. Overproduction of EGF occurred after the 70% Nx, was blunted in the 80% Nx, and then partially restored by phosphate restriction. Aggravation of tubular alteration was associated with enhanced renal hyperplasia (increased DNA mass), reduced GFR and hyperphosphatemia, and high PTH levels, but reduced cAMP excretion. Improvement following phosphate restriction was associated with reduced hyperplasia and lowering of phosphatemia and PTH levels. These data demonstrate that Nx selectively affected BBM function through transcriptional changes that were partially reversed by phosphate restriction. Regulatory factors involved in these changes may include intracellular phosphate content and growth factors, but not the PTH effects that are impaired in chronic renal failure.
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PMID:Subtotal nephrectomy alters tubular function: effect of phosphorus restriction. 940


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