Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The participation of ecto-ATP diphosphohydrolase (CD39; ecto-NTPDase) and ecto-5'-nucleotidase (CD73) activities in the nucleotide hydrolysis by salivary gland cells from rats was evaluated. We investigated the biochemical characteristics of these ectoenzymes in cells cultured from submandibular salivary glands of rats. The V(max) for the hydrolysis of ATP, ADP and AMP were 2275+/-153 (mean+/-SEM, n = 4), 941+/-96 (mean+/-SEM, n = 5) and 175+/-5 (mean+/-SEM, n = 5) nmol Pi liberated per min per mg of protein, respectively. The K(m) values for ATP, ADP and AMP were 224+/-8 microM (mean+/-SEM, n = 4), 163+/-15 microM (mean+/-SEM, n = 5) and 117+/-5 microM (mean+/-SEM, n = 5), respectively. The competition plot showed that ATP and ADP were hydrolyzed at the same active site on the enzyme. It may be postulated that the physiological role for this ecto-enzyme cascade is to terminate the action of the co-transmitter ATP, generating adenosine.
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PMID:Kinetic characterization of ATP diphosphohydrolase and 5'-nucleotidase activities in cells cultured from submandibular salivary glands of rats. 1648 Sep 2

An unknown epitope of apolipoprotein (a) antagonizes fibrinogen binding to agonist-stimulated platelet's fibrinogen (GPIIb/IIIa) receptor yielding lipoprotein (a) mediated decreased platelet aggregation. The purpose of this study was to test the hypothesis that human apolipoprotein (a)'s single arginyl-glycyl-aspartyl (RGD) epitope, unique to apolipoprotein (a) in lipoprotein (a) binds to the RGD binding motif on the IIb subunit of the GPIIb/IIIa receptor thus reducing platelet-bound fibrinogen and consequently decreasing agonist-stimulated platelet aggregation. Platelets (N=30 subjects) were prepared from fresh plasma, washed three times in Tyrode's buffer and stimulated using 10 microM ADP or 2 microg/ml collagen. Lipoprotein (a) was isolated from plasma using lectin affinity chromatography followed by ultracentrifugation. The peptide RGDS inhibited (125)I-labelled lipoprotein (a) binding to autologous platelets with IC-50's of 25.1+/-2.2 (mean+/-SEM) and 15.4+/-1.3 microM for collagen- and ADP-stimulation respectively. Further, RGDS reduced platelet binding of (125)I-labelled fibrinogen IC-50's of 35.5+/-3.2 (mean+/-SEM) and 20.7+/-2.2 microM for collagen- and ADP-stimulation respectively. The monoclonal antibody PAC-1, uniquely directed at the RGD binding motif on the IIb subunit on collagen- and ADP-stimulated platelets, inhibited binding of (125)I-labelled lipoprotein (a) with IC-50's of 6.4+/-0.7 and 2.5+/-2.2 microg/10(8) platelets for collagen- and ADP-stimulation respectively. Additionally, PAC-1 reduced platelet bound of (125)I-labelled fibrinogen with IC-50's of 9.0+/-1.4 and 4.1+/-2.2 microg/10(8) platelets for collagen- and ADP-stimulation respectively. In a dose-related fashion, a polyclonal antibody, specific for the RGD epitope on apolipoprotein (a), restored platelet aggregation to control levels, inhibited (125)I-labelled lipoprotein (a) binding, and increased (125)I-labelled fibrinogen by displacing lipoprotein (a) from the GPIIb/IIIa receptor. Thus a never before demonstrated aspect of the mechanism of lipoprotein (a)'s suggested novel role as an endogenous regulator of fibrinogen binding to collagen- and ADP-stimulated platelets has been shown. In conclusion, lipoprotein (a), via apolipoprotein (a)'s RGD epitope, binds to the RGD binding motif on the IIb protein of the GPIIb/IIIa receptor consequently reducing platelet-bound fibrinogen which results in decreased platelet aggregation.
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PMID:Arginyl-glycyl-aspartyl (RGD) epitope of human apolipoprotein (a) inhibits platelet aggregation by antagonizing the IIb subunit of the fibrinogen (GPIIb/IIIa) receptor. 1686 Mar 75

We reported earlier that hydroxyapatite (HA) formed on/in agarose gels (HA/agarose) produced by alternate soaking process is a bone-filling material possessing osteoconductive and hemostatic effects. This process could allow us to make bone-like apatite that was formed on/in organic polymer hydrogel matrices. Here, we investigated the mechanism of hemostasis induced by HA/agarose and found that HA/agarose, but not agarose or HA powder, significantly shortened activated partial thromboplastin time (APTT). While HA/agarose did not show significant platelet aggregation, it markedly enhanced adenosine diphosphate (ADP)-induced platelet aggregation. Moreover, Western blot analysis revealed selective adsorption of vitronectin onto HA/agarose. We also observed marked differences between HA powder and HA/agarose in their XRD patterns. The crystallinity of HA powder was much higher compared to that of HA/agarose. Furthermore, 50-100 nm of tube-form aggregations was observed in HA powder on the other hand 100-200 nm of particles was observed in HA/agarose by SEM observation. Thus 100-200 nm of low crystallized particles on the surface structure of HA/agarose may play an important role in hemostasis. Our results demonstrated a crucial role of HA/agarose in the mechanism of hemostasis and suggested a potential role for HA/agarose as a bone-grafting material.
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PMID:Hydroxyapatite formed on/in agarose gel induces activation of blood coagulation and platelets aggregation. 1702 65

In this study we describe the molecular identification, kinetic characterization and biochemical properties of an E-NTPDase and an 5'-nucleotidase in Walker 256 cells. For the ATP, ADP and AMP hydrolysis there were optimum pH in the range 6.5-8.0, and absolute requirement for divalent cations (Mg(2+)>Ca(2+)). A significant inhibition of ATP and ADP hydrolysis was observed in the presence of high concentrations of sodium azide and 0.5 mM of Gadolinium chloride. These activities were insensitive to ATPase, adenylate kinase and alkaline phosphatase classical inhibitors. The K(m) values were 464.2+/-86.6 microM (mean+/-SEM, n=4), 137.0+/-31 microM (mean+/-SEM, n=5) and 44.8+/-10.2 microM (mean+/-SEM, n=4), and V(max) values were 655.0+/-94.6 (mean+/-SEM, n=4), 236.3+/-27.2 (mean+/-SEM, n=5) and 177.6+/-13.8 (mean+/-SEM, n=5) nmol of inorganic phosphate min(-1) mg of protein(-1) for ATP, ADP and AMP, respectively. Using RT-PCR analysis we identified the mRNA of two members of the ecto-nucleoside triphosphate diphosphohydrolase family (NTPDase 2 and 5) and a 5'-nucleotidase. The presence of NTPDases and 5'-nucleotidase enzymes in Walker 256 tumor cells may be important to regulate the ratio adenine nucleotides/adenine nucleoside extracellularly, therefore motivating tumor growth.
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PMID:Nucleotide metabolizing ecto-enzymes in Walker 256 tumor cells: molecular identification, kinetic characterization and biochemical properties. 1716 79

Free fatty acids may create a state of continuous and progressive damaging to the vascular wall manifested by endothelial dysfunction. In this study we determine the mechanisms by which fatty acids palmitate (C16:0) and oleate (C18:1) affect intracellular long chain acyl-CoA (LCAC) content, energy metabolism, cell survival and proliferation and activation of NF-kappaB in cultured endothelial cells. A 48-h exposure of human umbilical vein endothelial cells (HUVEC) to 0.5 mM palmitate or 0.5 mM oleate increased total long chain acyl-CoA (LCAC) content 1.7 and 2 fold, respectively and decreased ATP(total)/ADP(total) ratio by 26+/-5% (mean+/-SEM) and 15+/-2%, respectively, which was prevented by the acyl-CoA synthetase inhibitor triacsin C. Furthermore, palmitate inhibited cell proliferation by 34+/-5%, while oleate stimulated it by 12+/-2%. alpha-Tocopherol fully and triacsin C partially abolished the effect of palmitate on cell proliferation. Palmitate and oleate increased caspase-3 activity 3.2 and 1.4 fold, respectively. Palmitate-induced caspase-3 activation was prevented by triacsin C and slightly reduced by alpha-tocopherol and by the de novo ceramide synthesis inhibitor fumonisin B(1). Both fatty acids induced antioxidant-sensitive nuclear translocation of NF-kappaB after 72 h, but not after 48 h. In conclusion, we showed that fatty acids influence different aspects of HUVEC function resulting in amongst other activation of apoptotic and inflammatory pathways. Our results indicate that the effects depend on the fatty acid type and may be related to accumulation of LCAC.
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PMID:Palmitate and oleate have distinct effects on the inflammatory phenotype of human endothelial cells. 1724 Jan 90

31P MRS offers a unique view of muscle metabolism in vivo, but correct quantification is important. Inter-study correlation of estimates of [Pi] and [phosphocreatine (PCr)] in a number of published studies suggest that the main technical problem in calibrated 31P MRS studies is the measurement of PCr and Pi signal intensities, rather than absolute quantification of [ATP]. For comparison, we discuss the few published biopsy studies of calf muscle and a selection of the many studies of quadriceps muscle. The ATP concentration is close to the value that we obtained in calf muscle in our own study, presented here, on four healthy subjects, by localised 31P MRS using a surface coil incorporating an internal reference and calibrated using an external phantom. However, the freeze-clamp biopsy PCr concentration is approximately 20% lower than the value obtained by 31P MRS, consistent with PCr breakdown by creatine kinase during freezing. Finally, we illustrate some consequences of uncertainty in resting [PCr] for analysis of mitochondrial function from PCr kinetics using a published 31P MRS study of exercise and recovery: the lower the assumed resting [PCr], the lower the absolute rate of oxidative ATP synthesis estimated from the PCr resynthesis rate; in addition, the lower the assumed resting [PCr], or the higher the assumed [total creatine], the higher the apparent resting [ADP], and therefore the more sigmoid the relationship between the rate of oxidative ATP synthesis and [ADP]. Correct quantification of resting metabolite concentrations is crucially important for this sort of analysis. Our own results ([PCr] = 33 +/- 2 mM, [Pi] = 4.5 +/- 0.2 mM, and [ATP] = 8.2 +/- 0.4 mM; mean +/- SEM) are close to the overall mean values of the 10 published studies on calf muscle by 'calibrated' 31P MRS (as in the present work), and of [PCr] and [Pi] in a representative selection of 'uncalibrated' 31P MRS studies (i.e. from measured PCr/ATP and Pi/ATP ratios, assuming a literature value for [ATP]).
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PMID:Absolute quantification of phosphorus metabolite concentrations in human muscle in vivo by 31P MRS: a quantitative review. 1762 42

Hemostasis is required to maintain vascular system integrity, but thrombosis, formation of a clot in a blood vessel, is one of the largest causes of morbidity and mortality in the industrialized world. Novel clinical and research tools for characterizing the hemostatic system are of continued interest, and the object of this research is to test the hypothesis that clinically relevant platelet function can be monitored using an electromechanical sensor. A piezoelectric thickness shear mode (TSM) biosensor coated with collagen-I fibers to promote platelet activation and adhesion was developed and tested for sensitivity to detect these primary events. Magnitude and frequency response of the sensor were monitored under static conditions at 37 degrees C, using platelet-rich plasma (PRP), and PRP with adenosine diphosphate (ADP), a clinical aggregation inhibitor (abciximab), or a collagen binding inhibitor. Sensors loaded with PRP exhibited a 3-stage response; no significant change in response for the first 20 min (Stage-1), followed by a larger drop in response (Stage-2) and subsequently, response gradually increased (Stage-3). Exogenous ADP stimulated an immediate Stage-2 response, while abciximab delayed and reduced the magnitude change of Stage-2. In the presence of collagen inhibitor, Stage-2 response was similar to that of control but was delayed by an additional 20 min. The obtained results, supported by epifluorescence and complementary SEM studies, demonstrated the selective sensitivity of TSM electromechanical biosensors to monitor platelet function and inhibition, particularly aggregation.
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PMID:Real-time monitoring of adhesion and aggregation of platelets using thickness shear mode (TSM) sensor. 1791 87

AMP-deaminase was purified to electrophoretic homogeneity from white skeletal muscle of a teleost fish, the common carp, Cyprinus carpio. The purified enzyme was highly stable and showed non-Michaelis-Menten kinetics with a S(0.5) value for AMP of 2.52+/-0.16 mM (SEM) and a Hill coefficient of 1.19+/-0.11. Specific activity of the purified enzyme was 1000-1200 U/mg protein. The pH optimum was 6.3 and the enzyme was activated by ADP and ATP, but inhibited by phosphate and fluoride. Low concentrations of NaCl and KCl (100-150 mM) activated, whereas higher concentrations were inhibitory. Free radicals inactivated the enzyme, decreasing V(max) by one-half but not affecting S(0.5) or Hill coefficient. Possible regulatory mechanisms of AMP-deaminase activity in fish muscle are discussed.
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PMID:Regulation of AMP-deaminase activity from white muscle of common carp Cyprinus carpio. 1806 Aug 19

Epidemiological studies indicate a J-shaped relationship linking coffee consumption and cardiovascular risk, suggesting that moderate coffee consumption can be beneficial. Platelet aggregation is of critical importance in thrombotic events, and platelets play a major role in the aetiology of several CVD. The aim of this study was to evaluate the effect of coffee drinking on platelet aggregation ex vivo, using caffeine as control. A crossover study was performed on ten healthy subjects. In two different sessions, subjects drank 200 ml coffee, containing 180 mg caffeine, or a capsule of caffeine (180 mg) with 200 ml water. Platelets were separated from plasma at baseline and 30 and 60 min after coffee drinking. Platelet aggregation was induced with three different agonists: collagen, arachidonic acid and ADP. Coffee drinking inhibited collagen (P < 0.05 from baseline at time 30 min) and arachidonic acid (P < 0.05 from baseline at time 60 min) induced platelet aggregation. Caffeine intake did not affect platelet aggregation induced by the three agonists. Coffee consumption induced a significant increase of platelet phenolic acids (likely present as glucuronate and sulphate derivatives), caffeic acid, the principal phenolic acid in coffee, raising from 0.3 (SEM 0.1) to 2.4 (SEM 0.6) ng/mg (P < 0.01). Caffeine was not detectable in platelets. Coffee drinking decreases platelet aggregation, and induces a significant increase in phenolic acid platelet concentration. The antiplatelet effect of coffee is independent from caffeine and could be a result of the interaction of coffee phenolic acids with the intracellular signalling network leading to platelet aggregation.
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PMID:Effect of coffee drinking on platelets: inhibition of aggregation and phenols incorporation. 1843 32

The aim of the study was to compare platelet activity between patients with an occlusion of bypass graft after coronary artery bypass graft surgery and restenosis after percutaneous coronary intervention (PCI); that is, between patients with reappearance of ischemia after two different kinds of coronary revascularization. Thirty patients were studied in a cross-sectional designed study. Fifteen of them were patients with the worst bypass graft patency from Prague-4 study (control protocol-driven coronary angiography performed at 1 year after surgery; originally 47 bypass grafts implanted, 94% of venous grafts occluded). The remaining 15 were patients with restenosis 3-12 months after PCI. Blood samples were drawn at least 12 weeks after coronary angiography. Platelet activity was determined by membrane expression of P-selectin (CD62P, % of positive cells) by flow cytometry, aggregability by ADP aggregometry. Data are expressed as mean +/- SEM. Both groups were similar with respect to age, BMI and presence of diabetes mellitus. No patient suffered from acute coronary syndrome. P-selectin expression was significantly higher in the patients with restenosis compared with patients with bypass graft occlusion (1.96 +/- 0.07 vs. 0.77 +/- 0.03, P < 0.001, Wilcoxon test). ADP aggregometry was not different between groups (55.5 +/- 1.1 vs. 56.1 +/- 0.8, P = NS). Higher platelet activity is present in the patients with restenosis after PCI compared with the patients with the occlusion of bypass graft. Platelet activity play more important role in the development of restenosis after PCI compared with the occlusion of bypass graft after coronary artery bypass graft surgery, at least in the period up to 1 year after revascularization.
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PMID:Higher platelet activity is present in patients with restenosis after percutaneous coronary intervention compared with patients with an occlusion of coronary artery bypass graft. 1900 48


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