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)

Epidermal growth factor (EGF) is now well known as a potent mitogen and differentiation factor for a variety of cells both in vivo and in vitro. Like other polypeptide hormones, EGF initially binds to a specific plasma membrane receptor on the target cells. In this study, we investigated the effect of streptozotocin-induced diabetes on EGF receptors on rat liver plasma membranes. An apparent increase in serum glucose concentration was observed in diabetic rats, and treatment of diabetic animals with insulin normalized the glucose concentration to the control level. There was no marked difference in hepatic membrane markers among the control, diabetic and insulin-treated diabetic animals, as judged by protein, sialic acid contents, and phosphodiesterase I and 5'-nucleotidase activities. The binding of 125I-EGF to membranes was found to be significantly lower in diabetic than in control animals. The value in diabetic animals was about 55% of the control level. Insulin treatment of diabetic animals restored the binding of 125I-EGF to the control level, whereas triiodothyronine (T3) treatment had no effect. Scatchard analysis of the binding data clearly showed that the decrease in EGF binding was due to a decrease in the number of receptors rather than to a change in receptor affinity. The decrease in EGF receptor number in diabetic animals was also confirmed by an experiment on affinity labeling of EGF receptors. EGF stimulated the phosphorylation of hepatic EGF receptors (molecular weight = 170,000). The rates of basal and EGF-stimulated phosphorylation of the receptors were lower in diabetic than in control animals. Insulin treatment of diabetic animals restored the phosphorylation activity to control level, whereas T3 treatment had no apparent effect. There was no significant difference in serum EGF concentration among the control, diabetic and insulin-treated diabetic animals. These results indicate that insulin deficiency in vivo causes a decrease in hepatic EGF receptor number, and suggest that the actions of EGF on hepatocytes may also be affected by diabetes mellitus since the effects of EGF are receptor-mediated.
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PMID:[Effect of experimental diabetes on epidermal growth factor (EGF) receptors in the rat liver]. 253 89

Cholesterol undergoes spontaneous autoxidation, leading to the production of potentially atherogenic oxidation derivatives. When 25-hydroxycholesterol (25-OH) or cholestane-3 beta, 5 alpha, 6 beta-triol (triol) was injected intravenously into rabbits, the aortic surfaces showed numerous balloon-like protrusions and crater-like defects indicative of endothelial damage. Alterations in membrane function caused by these cholesterol oxides could be the mechanism for their cytotoxic effect. Carrier-mediated hexose transport by cultured rabbit aortic smooth muscle cells, measured using 2-deoxyglucose, was reversibly inhibited by triol within one hour. A membrane-bound enzyme, 5'-nucleotidase, was inhibited after 24 to 48 hrs incubation with either 25-OH or triol. Endocytosis was also significantly inhibited by both 25-OH and triol. Depletion of membrane cholesterol content by the cholesterol oxides could account for the membrane functional alterations. Cholesterol biosynthesis is markedly inhibited by 25-OH. Triol has a lesser effect on cholesterol biosynthesis, but it is more potent in blocking uptake of cholesterol by arterial cells in culture. Cholesterol oxides may also influence cholesteryl ester accumulation by arterial smooth muscle cells. Incubation of cells with 25-OH resulted in a four-fold increase in cholesterol esterifying activity but no effect on cholesteryl ester hydrolytic activity. The cholesterol oxides appear to be transported in the blood primarily by very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Oxidized LDL has cytotoxic effects and enhances macrophage lipid accumulation. These be effects may be directly related to the cholesterol oxide content of these lipoproteins.
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PMID:The role of cholesterol oxidation products in the pathogenesis of atherosclerosis. 266 53

To investigate the mechanism by which glucocorticoids inhibit glucose transport in peripheral tissues, we have used a monoclonal antibody directed against the human glucose transporter to measure the relative amounts of glucose transporter polypeptide in various cell fractions of human foreskin fibroblasts after treatment with and without dexamethasone. In cells treated for 4 h with 100 nM dexamethasone, a decrease of 48% in glucose transport was accompanied by a decrease of 40% in the amount of glucose transporter polypeptide in a plasma membrane fraction enriched 10-fold in 5'-nucleotidase activity and a 78% increase in the amount of transporter polypeptide in a fraction of putative intracellular membranes, designated P2. There was no significant change in the amount of transporter polypeptide in whole cell lysates. Insulin (200 nM) stimulated glucose transport in basal fibroblasts by only 9%. However, addition of insulin for 30 min to cells that had been treated for 4 h with dexamethasone completely reversed the dexamethasone-induced decrease in glucose transport and also reversed the dexamethasone-induced changes in glucose transporter polypeptide content of the plasma membrane and P2 fractions. From these observations we conclude that dexamethasone decreases glucose transport by causing translocation of glucose transporters from the plasma membrane to an internal location and that insulin reverses the dexamethasone effect by reversing the translocation.
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PMID:Dexamethasone causes translocation of glucose transporters from the plasma membrane to an intracellular site in human fibroblasts. 282 29

To determine whether increased glucose transport following exercise is associated with an increased number of glucose transporters in muscle plasma membranes, the D-glucose inhibitable cytochalasin B binding technique was used to measure glucose transporters in red gastrocnemius muscle from exercised (1 h treadmill) or sedentary rats. Immediately following exercise there was a 2-fold increase in cytochalasin B binding sites, measured in purified plasma membranes enriched 30-fold in 5'-nucleotidase activity. This increase in glucose transporters in the plasma membrane may explain in part, the increase in glucose transport rate which persists in skeletal muscle following exercise. Where these transporters originate, remains to be elucidated.
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PMID:Acute exercise increases the number of plasma membrane glucose transporters in rat skeletal muscle. 284 99

Highly purified preparations of plasma membranes from control and ketoconazole-treated (1 microM, 120 h) epimastigotes of Trypanosoma cruzi have been obtained by cell disruption using abrasion with glass beads, differential centrifugation and isopycnic centrifugation in continuous, self-generating Percoll gradients. The purity of the preparation was ascertained by the specific activity 125I bound to the membranes obtained from enzymatically radiolabeled epimastigotes and by the alpha-methyl-mannoside sensitive binding of 125I-concanavalin A. The membranes form closed vesicles of 0.2-0.4 micron in diameter which display Mg2+ ATPase and acid phosphatase activities, but are devoid of 5'-nucleotidase and succinate-cytochrome c oxidoreductase; these vesicles can be strongly agglutinated by concanavalin A. The lipid order profiles of membranes from control and treated cells were compared with that present in egg phosphatidylcholine/ergosterol liposomes (84:16, mol/mol) by electron spin resonance spectroscopy of doxylstearic acid probes with the nitroxide group bound to carbon 5, 10, 12 and 16 of the stearic acid chain. Membranes from treated epimastigotes have a lipid order profile which resembles that of control plasma membranes near the polar surface (positions 5 and 10) but there is an abrupt decrease of order at position 12 and from there to the center of bilayer is highly disordered, even more than in pure lipid membranes. Consistent with these results, the leakage of L-[14C]glucose from membrane vesicles of ketoconazole-treated cells is much faster than that observed in vesicles obtained from control cells. These results indicate a strong alteration of the plasma membrane physical and biological properties due to the incubation of the parasite with the drug; this alteration is consistent with the accumulation of methylated precursors of ergosterol, which affects both lipid-lipid and lipid-protein interactions in the membrane.
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PMID:Alteration of lipid order profile and permeability of plasma membranes from Trypanosoma cruzi epimastigotes grown in the presence of ketoconazole. 284 68

Cyclic AMP has been implicated as a regulator of capacitation, but the control of its metabolism in sperm remains obscure. A recent study of mouse sperm has shown capacitation-related changes in the activities of both adenylate cyclase, which increased during incubation, and cyclic nucleotide phosphodiesterase, which decreased. The present study was conducted to extend these observations by measuring phosphodiesterase activity in sperm incubated in media with modified calcium and/or glucose content, conditions known to modulate fertilizing ability. Phosphodiesterase activity of sequential sperm samples, taken first when sperm are essentially uncapacitated and then when they are either partially or completely capacitated, decreased with time under all conditions, and in each case the greater fall in activity was seen in the medium that would support the greater change in fertilizing ability of the sperm population. Sperm washed by centrifugation to remove epididymal fluid also displayed a reduction in phosphodiesterase activity with time. The medium surrounding the sperm contained about half of the total phosphodiesterase activity, as well as 5'-nucleotidase and adenosine deaminase. The crude enzyme preparation showed complex kinetic behavior when assayed over a range of cAMP concentrations, but the reduction in activity with time was seen at all substrate levels. The observed changes in phosphodiesterase activity, together with the increased adenylate cyclase activity seen under these sperm incubation conditions, would increase cAMP availability with time, thus providing further evidence for a fundamental role for cAMP in controlling the events of capacitation.
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PMID:Phosphodiesterase activity of mouse sperm incubated under conditions that modulate fertilizing potential in vitro. 285 27

Of the various species of cellular 5'-nucleotidases, membranous, lysosomal and cytosolic, only the latter are likely to play a role in the physiologic dephosphorylation of the 5'-nucleoside monophosphates present in the cytoplasm. The necessity to preserve cellular ATP renders a strict control of the dephosphorylation as well as of the deamination of AMP mandatory, because both nucleotides are maintained in equilibrium by adenylate kinase. Our studies of cytosolic purine 5'-nucleotidases purified from rat liver and from human erythrocytes, reviewed in this presentation, have shown that both display complex kinetic properties. Both enzymes have markedly higher affinities for IMP and for GMP than for AMP. In addition, they are stimulated by nucleoside triphosphates, among them ATP and GTP, and inhibited by Pi. The erythrocytic purine 5'-nucleotidase is also stimulated by glycerate 2,3-bisphosphate. It could thus be expected that under conditions of ATP and GTP breakdown, particularly when accompanied by an increase in Pi, the dephosphorylation of AMP would be curtailed. To verify this hypothesis, experiments were performed with isolated rat hepatocytes and with human red blood cells. The rate of dephosphorylation of AMP was measured by following time-wise the production of adenosine in the presence of coformycin (or deoxycoformycin) and 5-iodotubercidin. The coformycins inhibit the deamination of adenosine into inosine by adenosine deaminase, and 5-iodotubercidin inhibits the recycling of adenosine into AMP by adenosine kinase. Upon induction of ATP catabolism by the addition of fructose to isolated rat hepatocytes, the dephosphorylation of AMP was nearly completely suppressed. In accordance with these results, the activity of the rat liver cytosolic 5'-nucleotidase, assayed in the presence of concentrations of substrate and effectors mimicking those measured in intact cells following the addition of fructose, was decreased as compared to control conditions. In hepatocytes in which ATP catabolism was induced by suppression of oxygen, the rate of dephosphorylation of AMP increased about 3-fold. However, in contradiction with these data, the activity of the cytosolic 5'-nucleotidase, measured under conditions mimicking anoxia, decreased markedly. In human erythrocytes, dephosphorylation of AMP did not occur under physiologic conditions, but proceeded when ATP catabolism was induced by glucose lack or by alkalinization. The rate of dephosphorylation of AMP was 3-fold higher during glucose deprivation than under alkaline conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Cytosolic purine 5'-nucleotidases of rat liver and human red blood cells: regulatory properties and role in AMP dephosphorylation. 285 49

The human monocytic leukemia cell line, THP-1, is induced to differentiate into more functionally mature monocyte (macrophage)-like cells by incubation with retinoic acid at concentrations of 10nM or higher. There is no apparent morphological change accompanying this functional maturation. These induced cells show increases in nitroblue tetrazolium reduction, immunoerythrophagocytosis, hexose monophosphate shunt activity, and 5'-nucleotidase and NAD+-glycohydrolase activities. Prostaglandin E2, dibutyryl cyclic adenosine 3':5'-monophosphate, or T-lymphocyte-derived differentiation-inducing activity, all inactive or less active alone, increase the extent of differentiation of THP-1 in combination with 10nM retinoic acid. THP-1 is also induced to differentiate by 0.1nM or higher concentrations of cholera toxin. Furthermore, 24,24-difluoro-1 alpha,25-dihydroxyvitamin D3 induces less differentiation of THP-1 compared to retinoic acid. Dimethyl sulfoxide and 12-O-tetradecanoylphorbol-13-acetate show no induction of functional differentiation. THP-1 thus joins the list of leukemic myelomonocytic cell lines (e.g., the promyelocytic HL-60 and the monoblast-like U-937) that are blocked at a relatively late stage of maturation and which differentiate in response to retinoic acid.
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PMID:Induction of functional differentiation of a human monocytic leukemia cell line (THP-1) by retinoic acid and cholera toxin. 298 63

We investigated the effect of irradiation on the kinetic characteristics of amino acid and glucose transport, and the effect on the activity of the cell membrane-bound enzyme 5'-nucleotidase and on the receptor-mediated stimulation of cyclic adenosine monophosphate synthesis by prostaglandin E1. Irradiation inhibited the sodium-dependent amino acid transport by a reduced binding of the amino acid to the transport unit. The transport of glucose, which appeared to be a sodium-independent process, was temporarily stimulated by increased maximal velocity of the transport. No effect was found on the binding to the transport unit. Irradiation increased the 5'-nucleotidase activity and decreased the prostaglandin E1-stimulated cyclic adenosine monophosphate synthesis 48 h after exposure to 20 Gy. It is concluded that irradiation decreases sodium-dependent transport by impairment of the transport unit, does not impair a sodium-independent process, and has opposite effects on membrane-bound enzyme activity and a receptor-mediated process.
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PMID:Radiation-induced changes in the cell membrane of cultured human endothelial cells. 300 20

Autoxidation derivatives of cholesterol known to affect cholesterol content of the cells were shown to alter some membrane associated functions in cultured aortic smooth muscle cells. For study of membrane-bound enzymes, Na+,K+-ATPase and 5'-nucleotidase were measured cytochemically by electron microscopy. Cells incubated with 10 ug/ml of cholestane-3 beta,5 alpha,6 beta-triol and 25-hydroxycholesterol for 24 to 48 hours showed marked inhibition of both enzyme activities. For study of carrier-mediated hexose transport, radiolabeled 2-deoxy-D-glucose was utilized. The uptake of this labeled compound was measured in the cells preincubated with oxidation derivatives of cholesterol for various time periods. Cholestane-3 beta,5 alpha,6 beta-triol had a rapid inhibitory effect on hexose transport, which was reversible after removal of the sterol from the medium. Hexose transport was not significantly altered by 25-hydroxycholesterol after up to 8 hours incubation. Two underlying mechanisms are possible. The prompt onset of the effect of cholestane-3 beta,5 alpha,6 beta-triol may be attributable to an incorporation of the sterol into the cell membranes. On the other hand, 25-hydroxycholesterol, a potent inhibitor of cholesterol biosynthesis, may have a delayed effect on membrane function by depleting the cholesterol available for membrane synthesis.
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PMID:Effects on membrane function by cholesterol oxidation derivatives in cultured aortic smooth muscle cells. 303 30


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