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Membrane Composition (membrane + composition)
Selected AbstractsAmperometric Sensor for Heparin: Sensing Mechanism and Application in Human Blood Plasma AnalysisELECTROANALYSIS, Issue 13-14 2006Jan Langmaier Abstract Voltammetric measurements of heparin at a rotating glassy carbon (GC) electrode coated with a polyvinylchloride membrane are reported. A spin-coating technique is used to prepare thin membranes (20,40,,m) with a composition of 25% (w/w) PVC, 1,1,-dimethylferrocene as a reference electron donor for the GC|membrane interface, nitrophenyl octyl ether (o -NPOE) or bis(2-ethylhexyl) sebacate (DOS) as a plasticizer, and hexadecyltrimethylammonium tetrakis(4-chlorophenyl) borate (HTMATPBCl) or tridodecylmethylammonium tetrakis(4-chlorophenyl) borate (TDMATPBCl) as a background electrolyte. It is shown that the electrodes coated with either the HTMA+/o -NPOE (DOS) or TDMA+/o -NPOE (DOS) membrane provide a comparable amperometric response towards heparin (1,10,U mL,1) in the aqueous solution of 0.1,M LiCl. However, only the membranes formulated with TDMATPBCl can be used for an amperometric assay of heparin in human blood plasma with a detection limit of 0.2,U mL,1. Effects of membrane composition, heparin concentration, rotation speed and sweep rate on the voltammetric behavior of heparin provide some insight into the sensing mechanism. Theoretical analysis of the amperometric response is outlined, and the numeric simulation of the voltammetric behavior is presented. [source] Galvanostatic Polarization of All-Solid-State K+ -Selective Electrodes with Polypyrrole Ion-to-Electron TransducerELECTROANALYSIS, Issue 13-14 2006owski Abstract Influence of galvanostatic polarizations on potential vs. logarithm of ion activity dependences of all-solid-state ion-selective electrodes with conducting polymer ion-to-electron transducer was studied. As a model system K+ -sensor with polypyrrole solid contact and poly(vinyl chloride) based membrane containing valinomycin was chosen. The influence of the lipophilic salt included to the membrane composition was of special interest. [source] Iodide-Selective Electrode Based on Copper PhthalocyanineELECTROANALYSIS, Issue 23 2002Saeed Shahrokhian Abstract Copper phthalocyanine was used as ion carrier for preparing polymeric membrane selective sensor for detection of iodide. The electrode was prepared by incorporating the ionophore into plasticized poly(vinyl chloride) (PVC) membrane, coated on the surface of graphite electrode. This novel electrode shows high selectivity for iodide with respect to many common inorganic and organic anions. The effects of membrane composition, pH and the influence of lipophilic cationic and anionic additives and also nature of plasticizer on the response characteristics of the electrode were investigated. A calibration plot with near-Nernestian slope for iodide was observed over a wide linear range of five decades of concentration (5×10,6,1×10,1,M). The electrode has a fast response time, and micro-molar detection limit (ca. 1×10,6,M iodide) and could be used over a wide pH range of 3.0,8.0. Application of the electrode to the potentiometric titration of iodide ion with silver nitrate is reported. This sensor is used for determination of the minute amounts of iodide in lake water samples. [source] Fatty acid incorporation in endothelial cells and effects on endothelial nitric oxide synthaseEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 9 2007S. Couloubaly Abstract Background The nature of fatty acids provided by the diet as well as plasma lipid metabolism can modify the composition and properties of plasma membrane and thus the activity of membrane proteins. In humans, as well as in experimental models, diabetes is associated with both an alteration in serum lipid profile and a documented endothelial dysfunction. This in vitro study investigated on an immortalized human endothelial cell line (EA.hy 926) the specific effects of several free fatty acids (FFAs) on the composition of cellular membranes and the regulation of endothelial nitric oxide synthase (eNOS). Materials and methods 0·1% of lipid deprived serum was added to the incubation medium with 25 mm glucose in order to study the effects of individual fatty acids: myristic acid, palmitic acid, stearic acid, oleic acid or linoleic acid at 100 µm bound with albumin. The effects of the FFAs on the endothelial nitric oxide synthase were investigated on mRNA level by quantitative PCR, on protein level and Ser1177 phosphorylation by Western blot and on enzymatic activity on living cells using radiolabelled arginine. Results Free linoleic acid increased the membrane content in n-6 fatty acids (mainly C18: n-6 and its metabolites) with a decrease in saturated and monounsaturated fatty acids. These conditions decreased the basal eNOS activity and reduced the phosphorylation of eNOS-Ser1177 due to activation by histamine. Free palmitic acid enriched the membranes with 16 : 0 with a slight decrease in monounsaturated fatty acids. These conditions increased eNOS activation without increasing Ser1177 phosphorylation upon histamine activation. The addition of the other FFAs also resulted in modifications of membrane composition, which did not to affect eNOS-Ser1177 phosphorylation. Conclusion Among the fatty acids used, only modification of the membrane composition due to linoleic acid supply disturbed the basal enzymatic activity and Ser1177 phosphorylation of eNOS in a way that limited the role of histamine activation. Linoleic acid might involve the dysfunction of both eNOS basal activity and its phosphorylation status and may then contribute to an impaired vasodilatation in vivo. [source] Characterization of potential stress responses in ancient Siberian permafrost psychroactive bacteriaFEMS MICROBIOLOGY ECOLOGY, Issue 1 2005Monica A. Ponder Abstract Past studies of cold-acclimated bacteria have focused primarily on organisms not capable of sub-zero growth. Siberian permafrost isolates Exiguobacterium sp. 255-15 and Psychrobacter sp. 273-4, which grow at subzero temperatures, were used to study cold-acclimated physiology. Changes in membrane composition and exopolysaccharides were defined as a function of growth at 24, 4 and ,2.5 °C in the presence and absence of 5% NaCl. As expected, there was a decrease in fatty acid saturation and chain length at the colder temperatures and a further decrease in the degree of saturation at higher osmolarity. A shift in carbon source utilization and antibiotic resistance occurred at 4 versus 24 °C growth, perhaps due to changes in the membrane transport. Some carbon substrates were used uniquely at 4 °C and, in general, increased antibiotic sensitivity was observed at 4 °C. All the permafrost strains tested were resistant to long-term freezing (1 year) and were not particularly unique in their UVC tolerance. Most of the tested isolates had moderate ice nucleation activity, and particularly interesting was the fact that the Gram-positive Exiguobacterium showed some soluble ice nucleation activity. In general the features measured suggest that the Siberian organisms have adapted to the conditions of long-term freezing at least for the temperatures of the Kolyma region which are ,10 to ,12 °C where intracellular water is likely not frozen. [source] Identification of phosphatidylserine decarboxylases 1 and 2 from Pichia pastorisFEMS YEAST RESEARCH, Issue 6 2009Tamara Wriessnegger Abstract Genetic manipulation of lipid biosynthetic enzymes allows modification of cellular membranes. We made use of this strategy and constructed mutants in phospholipid metabolism of Pichia pastoris, which is widely used in biotechnology for expression of heterologous proteins. Here we describe identification of two P. pastoris phosphatidylserine decarboxylases (PSDs) encoded by genes homologous to PSD1 and PSD2 from Saccharomyces cerevisiae. Using P. pastoris psd1, and psd2, mutants we investigated the contribution of the respective gene products to phosphatidylethanolamine synthesis, membrane composition and cell growth. Deletion of PSD1 caused loss of PSD activity in mitochondria, a severe growth defect on minimal media and depletion of cellular and mitochondrial phosphatidylethanolamine levels. This defect could not be compensated by Psd2p, but by supplementation with ethanolamine, which is the substrate for the cytidine diphosphate (CDP),ethanolamine pathway, the third route of phosphatidylethanolamine synthesis in yeast. Fatty acid analysis showed selectivity of both Psd1p and Psd2p in vivo for the synthesis of unsaturated phosphatidylethanolamine species. Phosphatidylethanolamine species containing palmitic acid (16:0), however, were preferentially assembled into mitochondria. In summary, this study provides first insight into membrane manipulation of P. pastoris, which may serve as a useful method to modify cell biological properties of this microorganism for biotechnological purposes. [source] Liquid,liquid extraction of cadmium(II) by Cyanex 923 and its application to a solid-supported liquid membrane systemJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2005Ana María Rodríguez Abstract The extraction of cadmium(II) by Cyanex 923 (a mixture of alkylphosphine oxides) in Solvesso 100 from hydrochloric acid solution has been investigated. The extraction reaction is exothermic. The numerical analysis of metal distribution data suggests the formation of CdCl2.2L, HCdCl3.2L and H2CdCl4.2L (L = ligand) in the organic phase. The results obtained for cadmium(II) distribution have been implemented in a solid-supported liquid membrane system. The influences of feed phase stirring speed (400,1400 min,1), membrane composition (carrier concentration: 0.06,1 mol dm,3) and metal concentration (0.01,0.08 g dm,3) on cadmium transport have been investigated. Copyright © 2005 Society of Chemical Industry [source] N,3 polyunsaturated fatty acids impair lifespan but have no role for metabolismAGING CELL, Issue 1 2007Teresa G. Valencak Summary Although generally considered as beneficial components of dietary fats, polyunsaturated fatty acids (PUFA) have been suspected to compromise maximum lifespan (MLSP) in mammals. Specifically, high amounts of phospholipid PUFAs are thought to impair lifespan due to an increase in the susceptibility of membranes to lipid peroxidation and its damaging effect on cellular molecules. Also, there is evidence from in vitro studies suggesting that highly unsaturated PUFAs elevate basal metabolic rate (BMR). Previous comparative studies in this context were based on small sample sizes, however, and, except for one study, failed to address possible confounding influences of body weight and taxonomic relations between species. Therefore, we determined phospholipid membrane composition in skeletal muscle from 42 mammalian species to test for a relation with published data on MLSP, and with literature data on BMR (30 species). Using statistical models that adjust for the effects of body weight and phylogeny, we found that among mammals, MLSP indeed decreases as the ratio of n,3 to n,6 PUFAs increases. In contrast to previous studies, we found, however, no relation between MLSP and either membrane unsaturation (i.e. PUFA content or number of double bonds) or to the very long-chain, highly unsaturated docosahexaenoic acid (DHA). Similarly, our data set gave no evidence for any notable relation between muscle phospholipid fatty acid composition and BMR, or MLSP and BMR in mammals. These results contradict the ,membrane pacemaker theory of aging', that is, the concept of a direct link between high amounts of membrane PUFAs, elevated BMR, and thus, impaired longevity. [source] Temperature dependence and resonance assignment of 13C NMR spectra of selectively and uniformly labeled fusion peptides associated with membranesMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2004Michele L. Bodner Abstract HIV-1 and influenza viral fusion peptides are biologically relevant model fusion systems and, in this study, their membrane-associated structures were probed by solid-state NMR 13C chemical shift measurements. The influenza peptide IFP-L2CF3N contained a 13C carbonyl label at Leu-2 and a 15N label at Phe-3 while the HIV-1 peptide HFP-UF8L9G10 was uniformly 13C and 15N labeled at Phe-8, Leu-9 and Gly-10. The membrane composition of the IFP-L2CF3N sample was POPC,POPG (4:1) and the membrane composition of the HFP-UF8L9G10 sample was a mixture of lipids and cholesterol which approximately reflects the lipid headgroup and cholesterol composition of host cells of the HIV-1 virus. In one-dimensional magic angle spinning spectra, labeled backbone 13C were selectively observed using a REDOR filter of the 13C,15N dipolar coupling. Backbone chemical shifts were very similar at ,50 and 20°C, which suggests that low temperature does not appreciably change the peptide structure. Relative to ,50°C, the 20°C spectra had narrower signals with lower integrated intensity, which is consistent with greater motion at the higher temperature. The Leu-2 chemical shift in the IFP-L2CF3N sample correlates with a helical structure at this residue and is consistent with detection of helical structure by other biophysical techniques. Two-dimensional 13C,13C correlation spectra were obtained for the HFP-UF8L9G10 sample and were used to assign the chemical shifts of all of the 13C labels in the peptide. Secondary shift analysis was consistent with a ,-strand structure over these three residues. The high signal-to-noise ratio of the 2D spectra suggests that membrane-associated fusion peptides with longer sequences of labeled amino acids can also be assigned with 2D and 3D methods. Copyright © 2004 John Wiley & Sons, Ltd. [source] Control of fatty acid desaturation: a mechanism conserved from bacteria to humansMOLECULAR MICROBIOLOGY, Issue 6 2006Pablo S. Aguilar Summary Unsaturated fatty acids (UFAs) have profound effects on the fluidity and function of biological membranes. Microorganisms, plants and animals regulate the synthesis of UFAs during changing environmental conditions as well as in response to nutrients. UFAs homeostasis in many organisms is achieved by feedback regulation of fatty acid desaturase gene transcription through signalling pathways that are governed by sensors embedded in cellular membranes. Here, we review recently discovered components of the regulatory machinery governing the transcription of fatty acid desaturases in bacteria, yeasts and animals that indicate an ancient role of transmembrane signalling mechanisms and integrate membrane composition with lipid biosynthesis. [source] Remodelling of the Escherichia coli outer membrane by two small regulatory RNAsMOLECULAR MICROBIOLOGY, Issue 1 2006Maude Guillier Summary Small non-coding RNAs that play important regulatory roles exist in numerous organisms. In Escherichia coli, about 60 small RNAs have been found and those that have been studied are involved in the response and adaptation to different stresses. RygA and RygB, two of these small RNAs, were identified on the basis of their conservation between different species and their ability to bind Hfq. They are adjacent on the chromosome and have sequence similarity at their 5, and 3, ends but distinct central regions, suggesting that they could regulate the expression of both common and distinct genes. A screen using a multicopy E. coli library led to identification of the response regulator OmpR and its associated sensor kinase EnvZ as positive regulators of rygA and rygB transcription. Therefore, RygA and RygB were renamed OmrA and OmrB respectively (for OmpR- regulated sRNAs A and B). When expressed at high levels, OmrA and OmrB RNAs negatively regulate the expression of several genes encoding multiple outer membrane proteins, including cirA, fecA, fepA and ompT. Taken together, these data suggest that OmrA and OmrB participate in the regulation of outer membrane composition in response to environmental conditions. [source] Does the lipid membrane composition of arsonoliposomes affect their anticancer activity?MOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 5 2009A cell culture study Abstract Sonicated arsonoliposomes were prepared using arsonolipid with palmitic acid acyl chain (C16), mixed with phosphatidylcholine (PC)-based or 1,2-distearoyl- sn -glycero-3-phosphocholine (DSPC)-based, and cholesterol (Chol) with C16/DSPC/Chol 8:12:10 molar ratio. PEG-lipid (1,2-distearoyl- sn -glycero-3-phosphoethanolamine conjugated to polyethylenoglycol 2000) containing vesicles (PEGylated-arsonoliposomes; PC-based and DSPC-based) were also prepared. The cytotoxicity of these arsonoliposomes towards different cancer cells (human promyelocytic leukaemia NB4, Prostatic cancer PC3, human breast adenocarcinoma MDA-MB-468, human T-lymphocyte (MT-4) and also towards human umbilical vein endothelial cells (HUVECs) was evaluated by calculating the arsonoliposome-induced growth inhibition of the cells by the MTT assay. IC-50 values were interpolated from cell number/arsonoliposome concentration curves. The results reveal that all types of arsonoliposomes evaluated significantly inhibit the growth of most of the cancer cells studied (PC3, NB4, MT4) with the exception of the MDA-MB-468 breast cancer cells which were minimally affected by arsonoliposomes; in some cases even less than HUVEC. Nevertheless, for the same cell type the differences between the different types of arsonoliposomes were significant but not proportional to their stability, indicating that the formation of arsonoliposomes with very stable membranes is not a problem for their anticancer activity. Thereby it is concluded that arsonoliposome composition should be adjusted in accordance to their in vivo kinetics and the desired, for each specific application, biodistribution of As and/or encapsulated drug. [source] Eicosapentaenoic acid and docosahexaenoic acid effects on tumour mitochondrial metabolism, acyl CoA metabolism and cell proliferationCELL BIOCHEMISTRY AND FUNCTION, Issue 2 2001Alison Colquhoun Abstract In order to investigate the effects of high-fat diets rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), Wistar rats bearing subcutaneous implants of the Walker 256 tumour were fed pelleted chow containing low DHA/EPA or high DHA/EPA. The presence of n -3 polyunsaturated fatty acids (PUFAs) led to a marked suppression (35,46%) of tumour growth over a 12 day period. Both the whole tumour homogenate and the Percoll-purified mitochondrial fraction presented significant changes in fatty acid composition. The levels of EPA increased in both n -3 dietary groups while the levels of DHA increased only in the high DHA/EPA group, in comparison with the control chow-fed group. The presence of n -3 PUFAs led to an increase in mitochondrial acyl CoA synthetase activity, but neither the cytoplasmic acyl CoA content nor the n -3 fatty acid composition of the cytoplasmic acyl CoAs was altered by the diet. The content of thiobarbituric acid-reactive substances (TBARS) was increased in the low DHA/EPA group but was unchanged in the high DHA/EPA group. In vitro studies with the Walker 256 cell line showed a 46% decrease in cell growth in the presence of either EPA or DHA which was accompanied by a large decrease in the measured mitochondrial membrane potential. The TBARS content was increased only in the EPA-exposed cells. Cell cycle analysis identified a decrease in G0,G1 phase cells and an increase in G2,M phase cells and apoptotic cells, for both EPA and DHA-exposed cells. The data show that the presence of n -3 PUFAs in the diet is able to significantly after the growth rate of the Walker 256 tumour. The involvement of changes in mitochondrial membrane composition and membrane potential have been indicated for both EPA and DHA, while changes in lipid peroxidation have been identified in the presence of EPA but not of DHA. Copyright © 2001 John Wiley & Sons, Ltd. [source] Isoprenoid pathway dysfunction in chronic fatigue syndromeACTA NEUROPSYCHIATRICA, Issue 5 2003Ravi Kumar Kurup Background and aims:, The isoprenoid pathway was assessed in 15 patients with chronic fatigue syndrome (CFS). The pathway was also assessed in individuals with differing hemispheric dominance to assess whether hemispheric dominance has any correlation with these disease states. Methods:, The isoprenoid metabolites , digoxin, dolichol and ubiquinone , RBC membrane Na+ -K+ ATPase activity, serum magnesium and tyrosine/tryptophan catabolic patterns were assessed. The free radical metabolism, glycoconjugate metabolism and RBC membrane composition were also assessed. Results:, Membrane Na+ -K+ ATPase activity and serum magnesium levels were decreased while HMG-CoA reductase activity and serum digoxin levels were increased in CFS. There were increased levels of tryptophan catabolites , nicotine, strychnine, quinolinic acid and serotonin , and decreased levels of tyrosine catabolites ,dopamine, norepinephrine and morphine , in CFS. There was an increase in dolichol levels, carbohydrate residues of glycoproteins, glycolipids, total/individual glycosaminoglycans (GAG) fractions and lysosomal enzymes in CFS. Reduced levels of ubiquinone, reduced glutathione and free radical scavenging enzymes as well as increased lipid peroxidation products and nitric oxide were noticed in CFS. The biochemical patterns in CFS correlated with those obtained in right hemispheric dominance. Conclusions:, The role of hypothalamic digoxin and neurotransmitter-induced immune activation, altered glycoconjugate metabolism and resultant defective viral antigen presentation, NMDA excitotoxicity and cognitive and mitochondrial dysfunction in the pathogenesis of CFS is stressed. CFS occurs in individuals with right hemispheric dominance. [source] Relationships between intestinal polyp formation and fatty acid levels in plasma, erythrocytes, and intestinal polyps in Min miceCANCER SCIENCE, Issue 12 2008Kiyonori Kuriki We have reported that a hyperlipidemic state is characteristic of Apc -deficient Min mice with multiple intestinal polyps. In our earlier case-control study, colorectal cancer risk showed positive relationships with erythrocyte membrane compositions of palmitic and oleic acids, but negative links with linoleic and arachidonic acids. To examine the roles of fatty acids in intestinal polyp formation, levels in plasma, erythrocytes, and intestinal polyps in Min mice were compared with those in wild-type mice. A diet free of eicosapentaenoic and docosahexaenoic acids with antineoplastic effects was fed to all mice from 6 to 15 weeks of age. Fatty acid levels were measured using accelerated solvent extraction and gas,liquid chromatography. Min mice with a hyperlipidemic state and multiple intestinal polyps had elevated values for palmitic and oleic acids in plasma and erythrocytes (at least P < 0.05), and higher plasma level of linoleic acid (P < 0.05). Arachidonic acid was 24.5% lower in erythrocytes (P < 0.0005), but did not differ in plasma. In Min mice, moreover, oleic and arachidonic acids were 1.78 and 1.43 times higher, respectively, in intestinal polyps than in paired normal mucosa (P < 0.05 and P < 0.01, respectively), but linoleic acid was 31.9% lower (P < 0.001). The present study suggests that palmitic, oleic, and arachidonic acids play key roles in intestinal polyp formation, and demonstrates reduced erythrocyte arachidonic acid values of Min mice, in line with our previous findings for patients with sporadic colorectal cancers. (Cancer Sci 2008; 99: 2410,2416) [source] | ||||||||||||||||