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

---

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

1. Adenylate cyclase (EC 4.6.1.1) activity was characterized in human liver, and its subcellular distribution compared with that of three other potential enzyme markers of the pericellular membrane: leucine aminopeptidase (EC 3.4.11.1), gamma-glutamyltransferase (EC 2.3.2.2) and 5'-nucleotidase (EC 3.1.3.5). Although these three enzyme activities were detected in each of the subcellular fractions studied, 85% of the total adenylate cyclase activity was found in the 1000 g pellet ('nuclear' fraction) with a threefold increase in specific activity as compared with the homogenate. No adenylate cyclase activity existed in the 150 000 g supernatant fraction. 2. In the 'nuclear' fraction, adenylate cyclase activity was increased in a dose-dependent fashion by glucagon with a half-maximal stimulation at 10 nmol/l and a maximal four- to seven-fold increase at 1 mumol/l. Catecholamines activated adenylate cyclase 2.5- to three-fold, with an order of potency (protokylol greater than isoprenaline greater than adrenaline greater than noradrenaline) typical of a beta 2-adrenoreceptor. Prostaglandin E1 and NaF also stimulated cyclase two- and four-fold respectively. Insulin, serotonin, dopamine, thyroid-stimulating hormone and ACTH had no effect. Adenosine provoked a weak inhibition at 0.1 mmol/l. Finally guanosine triphosphate and 5'-guanylyl imidodiphosphate induced a marked increase in basal activity, four- and eight-fold respectively, but both reduced the relative increase in enzyme activity due to glucagon or adrenaline. 3. Cyclase from foetal liver (12--16 weeks old) and cirrhotic adult liver appeared to behave similarly to that from normal liver; however, foetal cyclase was more active, and cirrhotic enzyme less active than normal adult liver. Both systems responded to catecholamines via a beta 2-adrenoreceptor. 4. These results validate the use of rat liver adenylate cyclase as a tool for pharmacological and physiological studies.
...
PMID:The adenylate cyclase system in human liver: characterization, subcellular distribution and hormonal sensitivity in normal or cirrhotic adult, and in foetal liver. 4 65

A rabbit antiserum to first-trimester human fetal tissue had greater reactivity in complement fixation and saturation binding assays with fetal tissues than with both a pool of normal adult lung, liver, and kidney and pools of the individual organs. This anti-fetal membrane reactivity was only partially inhibited by carcinoembryonic antigen. The serum still reacted strongly with human fetal and tumor cells after rendering it specific for plasma membrane components by adsorption to and elution from intact human fetal tissue culture cells. This plasma membrane-specific serum was then used to monitor the purification of the fetal membrane-associated antigens. The fetal antigens copurified with the putative plasma membrane enzymatic markers 5'-nucleotidase and Mg2+-adenosinetriphosphatase through differential and density gradient centrifugation. Insulin-binding activity only partially copurified with the antigenic activity. Little antigenic activity was found in nuclear and mitochondrial fractions. The isolation protocol gives fetal plasma membrane-associated antigens in approximately 50% yield with moderate purification. The sera and isolation procedures described should have general utility for the detection of human oncofetal antigens.
...
PMID:Isolation and partial characterization of plasma membranes bearing human fetal-associated antigens. 14 4

Insulin treatment of isolated liver plasma membranes induced the release of 5'-nucleotidase and alkaline phosphatase. This effect was maximal at physiological hormone concentrations, being 36% and 17% for 5'-nucleotidase and alkaline phosphatase respectively, and was fully mimicked by the phosphatidylinositol specific phospholipase C (PI-PLC), thus confirming the presence of a glycosylphosphatidylinositol anchoring-system for these exofacial enzymatic proteins. The complete inhibition of insulin dependent enzyme release by neomycin is strongly supportive of an involvement of membrane-located PI-PLC activity. In addition, the insulin-like effect on enzyme release induced by the GTP non-hydrolysable analog, GTP-gamma-S, and its sensitivity to the pertussis toxin are in favour of a mediatory role exerted by the G proteins system, in the transduction of some actions of insulin.
...
PMID:Insulin-dependent release of 5'-nucleotidase and alkaline phosphatase from liver plasma membranes. 133 52

The subcellular distribution of glucose transporters in rat hepatocytes and HepG2 cells was studied in the absence and in the presence of insulin. Glucose transporters were quantitated by measuring glucose-sensitive cytochalasin B binding and by protein immunoblotting using isoform-specific antibodies. Plasma membrane contamination into subcellular fractions was assessed by measuring distribution of 5'-nucleotidase and cell surface carbohydrate label. In hepatocytes, GLUT-2 occurred in a low-density microsomal (LDM) fraction at a significant concentration, and as much as 15% of cellular GLUT-2 was found intracellularly that cannot be accounted for by plasma membrane contamination. In HepG2 cells which express GLUT-1 and GLUT-2, the two isoforms showed distinct subcellular distribution patterns: GLUT-2 was highly concentrated in LDM while very little GLUT-1 was found in this fraction, indicating that a large portion of GLUT-2 occurs in intracellular organelles. Insulin treatment did not change the subcellular distribution patterns of glucose transporters in both cell types. Our results suggest that rat hepatocytes and HepG2 cells possess an intracellular storage pool for GLUT-2, but lack the insulin-responsive glucose transporter translocation mechanism.
...
PMID:Demonstration of an insulin-insensitive storage pool of glucose transporters in rat hepatocytes and HepG2 cells. 161 23

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.
...
PMID:[Effect of experimental diabetes on epidermal growth factor (EGF) receptors in the rat liver]. 253 89

To test the hypothesis of a defect in GH-receptor interaction, which could explain the growth failure of thalassemic children, the binding of [125I]human (h) GH to membrane fractions prepared from liver biopsies was studied. Small amounts of liver were obtained from 6 girls and 11 boys with homozygous beta-thalassemia, aged 3-15 yr, all prepubertal, at the time of splenectomy. Specific binding of [125I]hGH ranged from 0.37-5.11% of the added radioactivity/100 micrograms liver membrane protein, with variations in both receptor number and binding affinity. This 14-fold variation in hGH binding to liver membranes of thalassemic children was comparable to that in membrane fractions of livers obtained from normal donors at the time of liver transplant. The binding of insulin to liver membranes from the thalassemic patients ranged from 9.8-17.9% of the added radioactivity/100 micrograms membrane protein and from 2.8-15.0%/100 micrograms membrane protein in the normal donors. Insulin and GH binding to liver membranes did not vary in a consistent way. A 3-fold difference was found in 5'-nucleotidase activity of the membrane fractions. Histological hepatic modifications were assessed with respect to siderosis and fibrosis. No correlation was found between these parameters and GH binding. These results suggest that possible membrane alterations are not the only reason for the variations in hGH binding. All patients had retarded growth, and all but 2 had low plasma insulin-like growth factor I levels. No relationship was found between the level of GH binding to liver membranes and the growth failure. Thus, a defect in GH binding to liver membranes is probably not the cause of the growth retardation of thalassemic children.
...
PMID:No evidence for a defect in growth hormone binding to liver membranes in thalassemia major. 264 90

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.
...
PMID:Dexamethasone causes translocation of glucose transporters from the plasma membrane to an intracellular site in human fibroblasts. 282 29

Insulin releases inositol phosphoglycans from myocytes in culture [(1986) Science 233, 967-972], which display insulinomimetic activity. Because 5'-nucleotidase is anchored to the membrane through inositol-containing phospholipid glycans, we investigated whether insulin could release the enzyme from the membrane. Membranes prepared from hindquarter muscles of rats perfused with insulin showed a 23% decrease in 5'-nucleotidase activity. Isolated membranes from muscle exposed to insulin in vitro also showed a small but reproducible decrease (9%) in 5'-nucleotidase activity relative to unexposed controls. Phospholipase C from Staphylococcus aureus released 60% of the membrane-bound 5'-nucleotidase. We propose that insulin may activate an endogenous phospholipase C that cleaves phospholipid-glycan-anchored proteins.
...
PMID:Insulin-induced decrease in 5'-nucleotidase activity in skeletal muscle membranes. 284 8

Vmax of 5'-nucleotidase was found to be similar in liver plasmatic membranes of both 4-5 months old male rats and 24-26 months old animals. At the same time, Km value was higher in the membranes of old rats than in young animals. Insulin (administered at a dose of 2 un per 100 g of body mass) increased the enzyme Vmax without some age-dependent differences and decreased Km value in old animals as compared with controls.
...
PMID:[Age-dependent characteristics of the effect of insulin on 5'-nucleotidase activity in liver plasma membranes]. 300 38

Insulin receptors in human colon tumours, normal colon tissue and mesenteric fat removed at surgery have been identified by measuring the binding of labelled insulin to cell membrane preparations. Insulin binding sites were readily detected in all tissues, with mean +/- SD binding site concentrations of 43 +/- 41, 44 +/- 39, and 44 +/- 35fmol/mg membrane protein, and dissociation constants of 0.73 +/- 0.61, 0.66 +/- 0.41, and 0.78 +/- 0.58nM for microsomal plasma membrane preparations of tumour (n = 23) respectively. The specificity of binding of labelled insulin was similar in tumour and normal colon samples. Binding in normal colon preparations was highest in the epithelium (84fmol/mg membrane protein) and lower in lamina propria (19fmol/mg), submucosa (25fmol/mg) and muscle wall (13fmol/mg). Degradation of labelled insulin was similar in tumour and normal colon preparations. Mean receptor levels were not significantly different between microsomal membrane preparations and plasma membranes partially purified on discontinuous sucrose gradients, quantitated against either unit membrane protein or unit 5'-nucleotidase specific activity. There was a significant negative correlation between insulin levels, but no significant relationship was seen between serum insulin and receptor levels in either colon tumour or tissue preparations from full-thickness normal colon wall. An inverse correlation between serum insulin and receptor levels was, however, apparent in preparations of colonic musosa. These data indicate that although insulin receptors in colon tumours share the same biochemical characteristics as those present in the normal colon, receptors in tumour tissue are less sensitive to down-regulation by ambient insulin than receptors in mesenteric fat cells and normal colonic mucosa.
...
PMID:Insulin binding by normal and neoplastic colon tissue. 388 82


1 2 Next >>

---