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Membrane Transport (membrane + transport)
Terms modified by Membrane Transport Selected AbstractsMetagenomic approach studying the taxonomic and functional diversity of the bacterial community in a mesotrophic lake (Lac du Bourget , France)ENVIRONMENTAL MICROBIOLOGY, Issue 9 2009Didier Debroas Summary The main goals of this work were to identify the metabolic pathways of the bacterial community in a lacustrine ecosystem and to establish links between taxonomic composition and the relative abundances of these metabolic pathways. For this purpose, we analysed a 16S rRNA gene library obtained by gene amplification together with a sequence library of both insert ends on c. 7700 fosmids. Whatever the library used, Actinobacteria was the most abundant bacterial group, followed by Proteobacteria and Bacteroidetes. Specific aquatic clades such as acI and acIV (Actinobacteria) or LD12 and GOBB-C201 (Alphaproteobacteria) were found in both libraries. From comparative analysis of metagenomic libraries, the metagenome of this lake was characterized by overrepresentation of genes involved in the degradation of xenobiotics mainly associated with Alphaproteobacteria. Actinobacteria were mainly related to metabolic pathways involved in nucleotide metabolism, cofactors, vitamins, energy, replication and repair. Betaproteobacteria appeared to be characterized by the presence of numerous genes implicated in environmental information processing (membrane transport and signal transduction) whereas glycan and carbohydrate metabolism pathways were overrepresented in Bacteroidetes. These results prompted us to propose hypotheses on the ecological role of these bacterial classes in lacustrine ecosystems. [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] Predictive membrane transport model for nanofiltration processes in water treatmentAICHE JOURNAL, Issue 6 2001Shih-Chieh Tu A membrane transport model was developed for prediction and simulation of membrane filtration (nanofiltration) dynamics with reference to permeate flux. It incorporates important phenomenological aspects of membrane transport, such as concentration polarization and gel layer formation, and illustrates the concentration of solutes as foulants in the mass-transfer boundary layer on the membrane surface. Membrane filtration tests using tannic acid as a model organic compound were designed for investigating permeate fluxes, as well as solute concentration profiles for permeates and concentrates. Membrane performance experiments were conducted under various operation conditions by varying several parameters including solute concentrations, transmembrane pressures, and reject flow rates. The tests showed that the NF-45 membrane composed of polypiperazine amide was more susceptible to organic fouling by tannic acid than the NF-70 membrane made of cross-linked aromatic polyamide. These observations were supported by surface-potential measurements that demonstrated higher negative surface charges and greater hydrophilicity for the NF-70 membrane in the presence of tannic acid. The predictive capability of the membrane transport model was evaluated using the results from membrane filtration tests. Model sensitivity studies were conducted to obtain information on effects of various input parameters pertaining to operating conditions and fluid-dynamic regimes. [source] Poly(L-lysine) as a model drug macromolecule with which to investigate secondary structure and membrane transport, part I: physicochemical and stability studiesJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2002Montakarn Chittchang Low oral bioavailability of therapeutic peptides and proteins generally results from their poor permeability through biological membranes and enzymatic degradation in the gastrointestinal tract. Since different secondary structures exhibit different physicochemical properties such as hydrophobicity, size and shape, changing the secondary structure of a therapeutic polypeptide may be another approach to increasing its membrane permeation. Poly(L-lysine) was used as a model polypeptide. The objectives of this study were to induce secondary structural changes in poly(L-lysine) and to determine the time course over which a given conformer was retained. In addition, the hydrophobicity of each secondary structure of poly(L-lysine) was assessed. The circular dichroism (CD) studies demonstrated that the conditions employed could successfully induce the desired secondary structural changes in poly(L-lysine). The ,-helix conformer appeared to be more stable at 25° C whereas the ,-sheet conformer could be preserved at 37° C. On the other hand, the random coil conformer was retained at both temperatures. Significant losses of the ,-helix and the ,-sheet conformers were observed when the pH was reduced. The change in ionic strength did not affect any of the conformers. The octanol/buffer partitioning studies indicated that the ,-helix and the ,-sheet conformers exhibited significantly different (P< 0.05) hydrophobicities. In conclusion, variation of pH and temperature conditions can be used to induce secondary structural changes in poly(L-lysine). These changes are reversible when the stimuli are removed. The ,-helix and the ,-sheet conformers of poly(L-lysine) are more lipophilic than the native random coil conformer. Thus, poly(L-lysine) may represent an ideal model polypeptide with which to further investigate the effects of secondary structure on membrane diffusion or permeation. [source] Ion-pair mediated transport of small model peptides in liquid phase micro extraction under acidic conditionsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 3 2005J. Léon E. Reubsaet Abstract This paper discusses the behaviour of five small model peptides in a three phase (aqueous donor-organic-aqueous acceptor) liquid phase micro extraction system in relation to their physico-chemical properties (charge, hydrophobicity). It is proved that for all peptides transport over the organic phase is mediated by aliphatic sulphonic acids. Heptane-1-sulphonic acid gave the best overall recoveries. It appeared that peptides with hydrophobic properties (IPI) and a high number of positive charges (KYK) show good recoveries and are enriched in the acceptor phase. Variation in the pH (1.6,4.4) of the donor phase shows that there are peptide-dependent optimal pH-values for their recovery. Increasing pH in the acceptor phase shows that in most cases the recovery decreases due to decreased ion-pair mediated membrane transport. For KYK the partition between the organic phase and the aqueous acceptor-phase is also driven by the solubility in the aqueous acceptor phase. Increase of the ion strength of the acceptor phase did not affect the recovery of the peptides. Except for KYK, which showed decreased recovery when the ion strength increased. Another finding is that delocalisation of positive charge causes bad recovery, probably due to incomplete ion-pair-peptide complex formation. [source] Molecular mechanisms of membrane transport of vitamin EMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 5 2010Tappei Takada Abstract Vitamin E is an essential fat-soluble micronutrient for higher mammals and functions as an antioxidant for lipids and also as a regulator of gene expression and a modulator of cell signaling and proliferation. To exert its physiological functions, vitamin E must achieve an appropriate disposition throughout the body via several processes, such as intestinal absorption, uptake and efflux in peripheral tissues and biliary secretion. In this review, we mainly discuss membrane proteins involved in these transport processes (ATP-binding cassette transporter A1, scavenger receptor class B type I, Niemann-Pick C1-like 1 and multidrug resistance 3) and vitamin E-mediated regulation of their expression. [source] A novel procedure for gentle isolation and separation of intact infected and uninfected protoplasts from the central tissue of Vicia faba L. root nodulesPLANT CELL & ENVIRONMENT, Issue 7 2003E. PEITER ABSTRACT The central tissue of Vicia faba L. root nodules is composed of cells infected with Rhizobium bacteroids and uninfected cells. For the study of various processes, such as plasma membrane transport, it is essential to separate both cell types. Initial attempts to isolate protoplasts according to protocols described in the literature resulted in non-spherical and osmotically inactive material, which is in agreement with previous descriptions. In the study reported herein, it was shown that the plasma membrane of non-spherical infected protoplasts is not intact. A new isolation and separation protocol was developed, based on dissection of the nodule prior to cell wall digestion, non-shaking digestion in hypertonic medium, and a combined procedure for release of protoplasts into slightly hypotonic medium and separation of protoplast fractions by isopycnic density gradient centrifugation. Infected and uninfected protoplasts that were isolated according to this protocol were spherical, osmotically active and excluded propidium iodide, confirming the intactness of their plasma membrane. The common fluorescein diacetate test was shown to be artefactual in infected cells, since viable bacteroids also stain in defective cells. Light and electron microscopic examination of infected protoplasts showed that protoplasts still contained starch after isolation and bacteroids in intact protoplasts had unusually high amounts of polyhydroxybutyrate. The vacuoles of infected protoplasts contained protein and membrane-enclosed structures, and were of non-acid pH; traits that are typical of protein storage vacuoles. [source] Phosphate uptake in Chara: membrane transport via Na/Pi cotransportPLANT CELL & ENVIRONMENT, Issue 2 2000R. J. Reid ABSTRACT Phosphate uptake in the freshwater charophyte plant Chara corallina was found to be strongly dependent on the presence of Na in the external medium. Based on the reciprocal stimulations of 32Pi uptake by Na and 22Na uptake by Pi, the logical mechanism for Pi uptake appears to be a nNa/Pi symport with a half-maximal stimulation (Km) for Na of approximately 300 ,M and a Km for Pi of approximately 10 ,M. Comparison of the stimulations of 32Pi and 22Na influxes at pH 6 gives a stoichiometry of Na : Pi of 5·68. The reduction in Pi influx with increasing pH is consistent with the transported species being the monovalent H2PO4,. In voltage-clamp experiments, currents elicited by Pi in the presence of Na were equivalent to an influx of positive charge which exceeded the measured influxes of 32P by a factor of 6·26. Intracellular perfusion was used to examine the dependence of Pi influx on ATP and Na. In perfused cells, Pi influx was low when ATP was absent from the internal medium or Na was absent from the external medium. Addition of ATP alone had little effect whereas addition of Na alone increased the 32Pi influx slightly. Addition of both ATP and Na together restored Pi influx to rates comparable to those of intact cells. It is suggested that the ATP is required for membrane hyperpolarization which in turn drives the highly electrogenic flux of Pi with up to 6 Na. However, consideration of the electrochemical potential differences for Na and Pi at pH less than 6 shows that nNa/Pi would not be feasible. It is suggested that at low pH, H+ may substitute for Na. [source] Growth of the vacuoleless mutant of Tetrahymena thermophila NP1 in phytateTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005SAMANTHA WEBB Phytate, the salt form of phytic acid, is the major store of phosphate in seeds and grain. Since non-ruminant farm animals poorly digest phytate, it is also a source of environmental phosphate contamination in agricultural areas. We are using Tetrahymena, a ciliated protist with multiple routes for nutrient assimilation, as a model to investigate the contribution of heterotrophic protists to the environmental cycling of phosphate from phytate. This ciliate has the ability to grow on phytate as the sole phosphate source (Ziemkiewicz, H. T., Johnson, M. D. & Smith-Somerville, H. E. 2002. J. Eukaryot. Microbiol., 49:428). Tetrahymena thermophila NP1, a temperature-sensitive vacuoleless mutant (ATCC #50202), provides a way to separate membrane transport from uptake through phagosomes, and to assess the importance of each mechanism. This cell grows equally well at the permissive and non-permissive temperatures with either phytate or inorganic phosphate as the phosphate source. Our results demonstrate that phagosomes are not required to use the phosphate from phytate. [source] The effect of intracellular acidification on the relationship between cell volume and membrane potential in amphibian skeletal muscleTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005James A. Fraser The relationship between cell volume (Vc) and membrane potential (Em) in Rana temporaria striated muscle fibres was investigated under different conditions of intracellular acidification. Confocal microscope xz -scanning monitored the changes in Vc, whilst conventional KCl and pH-sensitive microelectrodes measured Em and intracellular pH (pHi), respectively. Applications of Ringer solutions with added NH4Cl induced rapid reductions in Vc that rapidly reversed upon their withdrawal. These could be directly attributed to the related alterations in extracellular tonicity. However: (1) a slower and persistent decrease in Vc followed the NH4Cl withdrawal, leaving Vc up to 10% below its resting value; (2) similar sustained decreases in resting Vc were produced by the addition and subsequent withdrawal of extracellular solutions in which NaCl was isosmotically replaced with NH4Cl; (3) the same manoeuvres also produced a marked intracellular acidification, that depended upon the duration of the preceding exposure to NH4Cl, of up to 0.53 ± 0.10 pH units; and (4) the corresponding reductions in Vc similarly increased with this exposure time. These reductions in Vc persisted and became more rapid with Cl, deprivation, thus excluding mechanisms involving either direct or indirect actions of pHi upon Cl, -dependent membrane transport. However they were abolished by the Na+,K+ -ATPase inhibitor ouabain. The Em changes that accompanied the addition and withdrawal of NH4+ conformed to a Nernst equation modified to include realistic NH4+ permeability terms, and thus the withdrawal of NH4+ restored Em to close to control values despite a persistent change in Vc. Finally these Em changes persisted and assumed faster kinetics with Cl, deprivation. The relative changes in Vc, Em and pHi were compared to predictions from the recent model of Fraser and Huang published in 2004 that related steady-state values of Vc and Em to the mean charge valency (zx) of intracellular membrane-impermeant anions, X,i. By assuming accepted values of intracellular buffering capacity (,i), intracellular acidification was shown to produce quantitatively predictable decreases in Vc. These findings thus provide experimental evidence that titration of the anionic zx by increased intracellular [H+] causes cellular volume decrease in the presence of normal Na+,K+ - ATPase activity, with Cl, -dependent membrane fluxes only influencing the kinetics of such changes. [source] Reduced amino acid content in transgenic potato tubers due to antisense inhibition of the leaf H+/amino acid symporter StAAP1THE PLANT JOURNAL, Issue 2 2003Wolfgang Koch Summary Transport processes across the plasma membrane of leaf vascular tissue are essential for transport and distribution of assimilates. In potato, leaves are the predominant sites for nitrate reduction and amino acid biosynthesis. From there, assimilated amino acids are exported through the phloem to supply tubers with organic nitrogen. To study the role of amino acid transporters in long-distance transport and allocation of organic nitrogen in potato plants, a gene encoding a functional, leaf-expressed amino acid permease StAAP1 was isolated. Similar to the sucrose transporter SUT1, StAAP1 expression was induced during the sink-to-source transition, indicating a role in phloem loading. To test the role of StAAP1, expression was inhibited by an antisense approach. Transgenic plants with reduced StAAP1 expression were phenotypically indistinguishable from wild type, as were photosynthetic capacity and tuber yield. However, tubers from antisense StAAP1 plants showed up to 50% reduction in free amino acid contents. In comparison, starch content was not affected or tended to increase relative to wild type. The reduction in all amino acids except aspartate in the antisense plants is consistent with the properties of amino acid permeases (AAPs) found in heterologous systems. The results demonstrate an important role for StAAP1 in long-distance transport of amino acids and highlight the importance of plasma membrane transport for nutrient distribution in plants. [source] Analysis of vitamin D-regulated gene expression in LNCaP human prostate cancer cells using cDNA microarraysTHE PROSTATE, Issue 3 2004Aruna V. Krishnan Abstract BACKGROUND 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] exerts growth inhibitory, pro-differentiating, and pro-apoptotic effects on prostate cells. To better understand the molecular mechanisms underlying these actions, we employed cDNA microarrays to study 1,25(OH)2D3 -regulated gene expression in the LNCaP human prostate cancer cells. METHODS mRNA isolated from LNCaP cells treated with vehicle or 50 nM 1,25(OH)2D3 for various lengths of time were hybridized to microarrays carrying approximately 23,000 genes. Some of the putative target genes revealed by the microarray analysis were verified by real-time PCR assays. RESULTS 1,25(OH)2D3 most substantially increased the expression of the insulin-like growth factor binding protein-3 (IGFBP-3) gene. Our analysis also revealed several novel 1,25(OH)2D3 -responsive genes. Interestingly, some of the key genes regulated by 1,25(OH)2D3 are also androgen-responsive genes. 1,25(OH)2D3 also down-regulated genes that mediate androgen catabolism. CONCLUSIONS The putative 1,25(OH)2D3 target genes appear to be involved in a variety of cellular functions including growth regulation, differentiation, membrane transport, cell,cell and cell,matrix interactions, DNA repair, and inhibition of metastasis. The up-regulation of IGFBP-3 gene has been shown to be crucial in 1,25(OH)2D3 -mediated inhibition of LNCaP cell growth. 1,25(OH)2D3 regulation of androgen-responsive genes as well as genes involved in androgen catabolism suggests that there are interactions between 1,25(OH)2D3 and androgen signaling pathways in LNCaP cells. Further studies on the role of these genes and others in mediating the anti-cancer effects of 1,25(OH)2D3 may lead to better approaches to the prevention and treatment of prostate cancer. © 2004 Wiley-Liss, Inc. [source] Involvement of Iron (Ferric) Reduction in the Iron Absorption Mechanism of a Trivalent Iron-Protein Complex (Iron Protein SuccinylateBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 3 2000Kishor B. Raja Iron protein succinylate is a non-toxic therapeutic iron compound. We set out to characterise the structure of this compound and investigate the importance of digestion and intestinal reduction in determining absorption of the compound. The structure of the compound was investigated by variable temperature Mössbauer spectroscopy, molecular size determinations and kinetics of iron release by chelators. Intestinal uptake was determined with radioactive compound force fed to mice. Reduction of the compound was determined by in vitro incubation with intestinal fragments. The compound was found to contain only ferric iron, present as small particles including sizes below 10 nm. The iron was released rapidly to chelators. Digestion with trypsin reduced the molecular size of the compound. Intestinal absorption of the compound was inhibited by a ferrous chelator (ferrozine), indicating that reduction to ferrous iron may be important for absorption. The native compound was a poor substrate for duodenal reduction activity, but digestion with pepsin, followed by pancreatin, released soluble iron complexes with an increased reduction rate. We conclude that iron protein succinylate is absorbed by a mechanism involving digestion to release soluble, available ferric species which may be reduced at the mucosal surface to provide ferrous iron for membrane transport into enterocytes. [source] Expression, purification, crystallization and preliminary X-ray diffraction analysis of the TonB-dependent haem outer membrane transporter ShuA from Shigella dysenteriaeACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2009Karl Brillet As part of efforts towards understanding the crystallization of membrane proteins and membrane transport across the outer membrane of Gram-negative bacteria, the TonB-dependent haem outer membrane transporter ShuA of Shigella dysenteriae bound to heavy atoms was crystallized in several crystallization conditions using detergents. The insertion of a His6 tag into an extracellular loop of ShuA, instead of downstream of the Escherichia coli peptide signal, allowed efficient targeting to the outer membrane and the rapid preparation of crystallizable protein. Crystals diffracting X-rays beyond 3.5,Å resolution were obtained by co-crystallizing ShuA with useful heavy atoms for phasing (Eu, Tb, Pb) by the MAD method at the synchrotron, and the SAD or SIRAS method at the Cu wavelength. The authors collected X-ray diffraction data at 2.3,Å resolution using one crystal of ShuA-Pb, and at 3.2,Å resolution at an energy remote from the Pb,M absorption edges for phasing on PROXIMA-1 at SOLEIL. [source] Transport characteristics of L -citrulline in renal apical membrane of proximal tubular cellsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 3 2009Keisuke Mitsuoka Abstract L -Citrulline has diagnostic potential for renal function, because its plasma concentration increases with the progression of renal failure. Although L -citrulline extracted by glomerular filtration in kidney is mostly reabsorbed, the mechanism involved is not clearly understood. The present study was designed to characterize L -citrulline transport across the apical membranes of renal epithelial tubular cells, using primary-cultured rat renal proximal tubular cells, as well as the human kidney proximal tubular cell line HK-2. L -Citrulline was transported in a Na+ -dependent manner from the apical side of both cell types cultured on permeable supports with a microporous membrane. Kinetic analysis indicated that the transport involves two distinct Na+ -dependent saturable systems and one Na+ -independent saturable system in HK-2 cells. The uptake was competitively inhibited by neutral and cationic, but not anionic amino acids. Relatively large cationic and anionic compounds inhibited the uptake, but smaller ones did not. In HK-2 cells, mRNA expression of SLC6A19 and SLC7A9, which encode B0AT1 and b0,+AT, respectively, was detected by RT-PCR. In addition, L -citrulline transport was significantly decreased in HK-2 cells in which either SLC6A19 or SLC7A9 was silenced. Hence, these results suggest that amino acid transporters B0AT1 and b0,+AT are involved in the reabsorption of L -citrulline in the kidney, at least in part, by mediating the apical membrane transport of L -citrulline in renal tubule cells. Copyright © 2009 John Wiley & Sons, Ltd. [source] A Two-Photon Fluorescent Probe for Lipid Raft Imaging: C-LaurdanCHEMBIOCHEM, Issue 5 2007Hwan Myung Kim Abstract The lipid-rafts hypothesis proposes that naturally occurring lipid aggregates exist in the plane of membrane that are involved in signal transduction, protein sorting, and membrane transport. To understand their roles in cell biology, a direct visualization of such domains in living cells is essential. For this purpose, 6-dodecanoyl-2-(dimethylamino)naphthalene (laurdan), a membrane probe that is sensitive to the polarity of the membrane, has often been used. We have synthesized and characterized 6-dodecanoyl-2-[N -methyl- N -(carboxymethyl)amino]naphthalene (C-laurdan), which has the advantages of greater sensitivity to the membrane polarity, a brighter two-photon fluorescence image, and reflecting the cell environment more accurately than laurdan. Lipid rafts can be visualized by two-photon microscopy by using C-laurdan as a probe. Our results show that the lipid rafts cover 38,% of the cell surface. [source] | ||||||||||||||||||||||||||||