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Membrane Structure (membrane + structure)
Selected AbstractsEvaluation of Process-Induced Dimensional Changes in the Membrane Structure of Biological Cells Using Impedance MeasurementBIOTECHNOLOGY PROGRESS, Issue 3 2002Alexander Angersbach The impact of high intensity electric field pulses, high hydrostatic pressure, and freezing-thawing on local structural changes of the membrane was determined for potato, sugar beet tissue, and yeast suspensions. On the basis of the electrophysical model of cell systems in biological tissues and suspensions, a method was derived for determining the extent of local damage of cell membranes. The method was characterized by an accurate and rapid on-line determination of frequency-dependent electrical conductivity properties from which information on microscopic events on cellular level may be deduced. Evaluation was based on the measurement of the relative change in the sampleapos;s impedance at characteristically low ( fl) and high ( fh) frequencies within the ,-dispersion range. For plant and animal cells the characteristic frequencies were fl , 5 kHz and fh > 5 MHz and for yeast cells in the range fl , 50 kHz and fh > 25 MHz. The observed phenomena were complex. The identification of the underlying mechanisms required consideration of the time-dependent nature of the processing effects and stress reactions of the biological systems, which ranged from seconds to several hours. A very low but significantly detectable membrane damage (0.004% of the total area) was found after high hydrostatic pressure treatment of potato tissue at 200 MPa. The membrane rupture in plant tissue cells was higher after freezing and subsequent thawing (0.9% of total area for potato cells and 0.05,0.07% for sugar beet cells determined immediately after thawing), which increased substantially during the next 2 h. [source] Vacuolar membrane dynamics revealed by GFP-AtVam3 fusion proteinGENES TO CELLS, Issue 7 2002Tomohiro Uemura Background: The plant vacuole is a multifunctional organelle that has various physiological functions. The vacuole dynamically changes its function and shape, dependent on developmental and physiological conditions. Our current understanding of the dynamic processes of vacuolar morphogenesis has suffered from the lack of a marker for observing these processes in living cells. Results: We have developed transgenic Arabidopsis thaliana expressing a vacuolar syntaxin-related molecule (AtVam3/SYP22) fused with green fluorescent protein (GFP). Observations using confocal laser scanning microscopy demonstrated that the plant vacuole contained a dynamic membrane system that underwent a complex architectural remodelling. Three-dimensional reconstitution and time-lapse analysis of GFP-fluorescence images revealed that cylindrical and sheet-like structures were present in the vacuolar lumen and were moving dynamically. The movement, but not the structure itself, was abolished by cytochalasin D, an inhibitor of actin polymerization. This moving structure, which sometimes penetrated through the vacuolar lumen, possessed a dynamic membrane architecture similar to the previously recognized ,transvacuolar strand.' Conclusion: We propose two possible models for the formation of the vacuolar lumenal structure. Membrane structures including protruding tubules and reticular networks have recently been recognized in many other organelles, and may be actively involved in intra- and/or inter-organelle signalling. [source] MBSJ MCC Young Scientist Award 2009 REVIEW: Selective autophagy regulates various cellular functionsGENES TO CELLS, Issue 9 2010Masaaki Komatsu Autophagy is a self-eating system conserved among eukaryotes, in which cellular components including organelles are entrapped into a double membrane structure called the autophagosome and then degraded by lysosomal hydrolases. In addition to its role in supplying amino acids in response to nutrient starvation, autophagy is involved in quality control to maintain cell health. Thus, inactivation of autophagy causes the formation of cytoplasmic protein inclusions, which comprise misfolded proteins and the accumulation of many degenerated organelles, resulting in liver injury, diabetes, myopathy and neurodegeneration. Furthermore, although autophagy has been considered nonselective, increasing evidence points to the selectivity of autophagy in sorting vacuolar enzymes and removal of aggregate-prone proteins and unwanted organelles. Such selectivity allows diverse cellular regulation, similar to the ubiquitin proteasome pathway. In this review, we discuss the physiological roles of selective autophagy and their molecular mechanisms. [source] Stratum corneum keratin structure, function and formation , a comprehensive reviewINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 6 2006L. Norlén Synopsis A comprehensive review on stratum corneum keratin organization, largely based on the recently published cubic rod-packing and membrane templating model [J. Invest. Dermatol., 123, 2004, 715], is presented. Keratin is the major non-aqueous component (wt/wt) of stratum corneum. As 90,100% of the stratum corneum water is thought to be located intracellularly one may presume that keratin also is a major factor (together with filaggrin-derived free amino acids) determining stratum corneum hydration level and water holding capacity. This water holding capacity depends in turn on the structural organization of the corneocyte keratin intermediate filament network. The cubic rod-packing model for the structure and function of the stratum corneum cell matrix postulates that corneocyte keratin filaments are arranged according to a cubic-like rod-packing symmetry. It is in accordance with the cryo-electron density pattern of the native corneocyte keratin matrix and could account for the swelling behaviour and the mechanical properties of mammalian stratum corneum. The membrane templating model for keratin dynamics and for the formation of the stratum corneum cell matrix postulates the presence in viable epidermal cellular space of a highly dynamic small lattice parameter (<30 nm) membrane structure with cubic-like symmetry, to which keratin is associated. It further proposes that membrane templating, rather than spontaneous self-assembly, is responsible for keratin intermediate filament formation and dynamics. It is in accordance with the cryo-electron density patterns of the native keratinocyte cytoplasmic space and could account for the characteristic features of the keratin network formation process, the dynamic properties of keratin intermediate filaments, the close lipid association of keratin, the insolubility in non-denaturating buffers and pronounced polymorphism of keratin assembled in vitro, and the measured reduction in cell-volume and hydration level between stratum granulosum and stratum corneum. Résumé, La kératine est le composant majeur anhydre de la couche cornée. Etant donné que l'on considère que 90 à 100% de l'eau de la couche cornée est localisée à l'intérieur des cellules, on peut penser que la kératine joue également un rôle important (en association avec les acides aminés libres dérivés de la filagrine) dans le niveau d'hydratation de la couche cornée et sa capacité de rétention de l'eau. Cette capacité de rétention de l'eau dépend elle-même de l'organization structurelle du réseau de filaments intermédiaires de la kératine des cornéocytes. Le modèle de cylindre en réseau cubique appliquéà la structure et aux fonctions de la matrice des cellules de la couche cornée stipule que les filaments de la kératine des cornéocytes sont disposés symétriquement, les paquets de fibrilles formant une structure cubique. Ceci est conforme au modèle de densité cryo-électronique de la matrice kératinique des cornéocytes natifs et pourrait expliquer le comportement de gonflement et les propriétés mécaniques de la couche cornée des mammifères. Le modèle d'assemblage membranaire appliquéà la dynamique de la kératine et à la formation de la matrice cellulaire du stratum cornéum postule la présence dans l'espace cellulaire viable de l'épiderme d'une structure membranaire hautement dynamique présentant un petit paramètre de maille (<30 nm) et une organization en forme de cube, à laquelle la kératine est associée. D'autre part, ce modèle suggère qu'un assemblage membranaire plutôt qu'un auto-assemblage spontané puisse être à l'origine de la formation des filaments intermédiaires de kératine et de leur dynamique. Ceci concorde avec les modèles de densité cryo-électronique du cytoplasme des kératinocytes natifs et pourrait expliquer les caractéristiques du processus de formation du réseau kératinique, les propriétés dynamiques des filaments intermédiaires de kératine, l'association de la kératine avec les lipides, l'insolubilité dans les tampons non dénaturants, le polymorphisme caractéristique de la kératine assemblée in vitro, ainsi que la diminution mesurée du volume cellulaire et du niveau d'hydratation entre le stratum granulosum et le stratum corneum. [source] Novel free energy calculations to explore mechanisms and energetics of membrane protein structure and functionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2009Wonpil Im Abstract Understanding the delicate balance of forces governing helix or ,-hairpin interactions in transmembrane (TM) proteins is central to understanding membrane structure and function. These membrane constituent interactions play an essential role in determining the structure and function of membrane proteins, and protein interactions in membranes, and thus form the basis for many vital processes, including TM signaling, transport of ions and small molecules, energy transduction, and cell,cell recognition. "Why does a single-pass TM helix or ,-hairpin have specific orientations in membranes?" "What are the roles of hydrogen bonds, close packing, and helix-lipid or ,-hairpin-lipid interactions in helix or ,-hairpin associations in membranes?" "How do these interactions change the membrane structures?" "How do TM domains transmit signals across membranes?" These are important membrane biophysical questions that can be addressed by understanding the delicate balance of forces governing helix or ,-hairpin interactions with/in membranes. In this work, we summarize a series of helix/,-hairpin restraint potentials that we have developed, and illustrate their applications that begin to address the complicated energetics and molecular mechanisms of these interactions at the atomic level by calculating the potentials of mean force (PMFs) along reaction coordinates relevant to helix/,-hairpin motions in membranes and dissecting the total PMF into the contributions arising from physically important microscopic forces. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Simulations of the active transport of a neutral solute based on a kinase-channel-phosphatase topologyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2005K. Fiaty Abstract Simulations of coupled interactions involving two opposite enzymatic reactions, solute diffusions, and electrostatic interactions between membrane charges and charged solutes were conducted under a fixed kinase-channel-phosphatase (KCP) topology oriented from the outside to the inside of a porous membrane structure. Depending on the kinase and phosphatase locations, we recently demonstrated that an active transport of a phosphorylated substrate may occur via the opposite topology, that is, a PCK topology. The present analysis demonstrates that, under a KCP membrane topology, which also behaves as a specific ATP-dependent transporter, the active transport of a neutral substrate may occur. This analogous active transport appears to be dependent on the phosphatase location and on the membrane surface potentials. A broad analysis of the role played by the main parameters taken into account in the model was conducted in order to define precisely the physico-chemical conditions and the membrane topology needed for the highest active transports within the shortest time. © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 201,213, 2005 [source] Theoretical analysis of the effects of asymmetric membrane structure on fouling during microfiltrationAICHE JOURNAL, Issue 6 2009Weiyi Li Abstract There is a growing interest in the use of both asymmetric and composite membranes for microfiltration and ultrafiltration processes. This includes particle removal applications in the semiconductor industry and virus clearance in biopharmaceutical applications. Filter fouling plays an important role in these processes. Although flux decline models have been developed for homogeneous membranes, the effects of asymmetric membrane structure on flux decline behavior remain poorly understood on a fundamental level. Here, we develop a theoretical model to describe the effects of asymmetric membrane structure on flux decline. The asymmetric structure was described by the spatial variation in Darcy permeability in the directions normal to and parallel to the membrane surface. The velocity profile and flux decline because of pore blockage were described using Darcy's law and a pore blockage and cake filtration model. Flux decline data were obtained using pseudocomposite membranes with highly interconnected polyvinylidene fluoride membranes (PVDF) and straight through pore polycarbonate track-etched membranes (PCTE). Model composite membranes were formed by layering PCTE or PVDF membranes with different pore sizes on top of each other. Flux decline data for the composite membrane were in good agreement with model calculations. The results provide important insights into the effects of asymmetric membrane pore structures on flux decline. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Melatonin applied to cucumber (Cucumis sativus L.) seeds improves germination during chilling stressJOURNAL OF PINEAL RESEARCH, Issue 2 2009gorzata M. Posmyk Abstract:, The relationship between germination and melatonin applied during osmo- and hydropriming was studied in cucumber seeds. The proportion of nuclei with different DNA contents, the mean ploidy and the (2C + 4C = 8C)/2C ratio in unprimed and primed, dry and imbibed at 10°C seeds were established by flow cytometry. Thiobarbituric acid reactive substances and protein oxidation were also estimated. Melatonin and indole-3-acetic acid (IAA) concentrations in the seeds were determined using high-performance liquid chromatography with electrochemical detection. Being sensitive to chilling stress, seeds that germinated well (99%) at 25°C showed only 30% germination at 15°C, and almost no germination (4%) at 10°C. Hydropriming in water improved seed germination to 50,60% at 15°C and the addition of melatonin (25,100 m) also increased the rate of germination. Osmopriming in polyethylene glycol increased germination at 15°C to 78%, and 98% when combined with 50 m melatonin. Osmoprimed seeds germinated even at 10°C and reached 43%, and 83% when 50 m melatonin was applied. None of the treatments induced DNA synthesis, although during the first 24 hr of imbibition at 10°C the mean ploidy and the (2C + 4C = 8C)/2C ratio increased, which is indicative of the advanced Phase II of germination. Hydro- and osmopriming slightly decreased IAA content in the seeds in most of the cases; only hydropriming with 100 and 500 m melatonin increased it. Melatonin protected membrane structure against peroxidation during chilling, but excessive melatonin levels in cucumber seeds (,4 ,g/g fresh weight) provoked oxidative changes in proteins. There is still lack of information explained clearly the role of melatonin in plant physiology. This molecule acts multidirectionally and usually is alliged to other compounds. [source] Synthesis of proton-conducting membranes by the utilization of preirradiation grafting and atom transfer radical polymerization techniquesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2002Svante Holmberg Abstract The atom transfer radical polymerization (ATRP) of styrene onto poly(vinylidene fluoride)- graft -poly(vinylbenzyl chloride) (PVDF- g -PVBC) membranes was investigated. Novel membranes were designed for fuel-cell applications. The benzyl chloride groups in the PVDF- g -PVBC membranes functioned as initiators, and a Cu-based catalytic system with the general formula Cu(n)Xn/ligand [where X is Cl or Br and the ligand is 2,2,-bipyridyl (bpy)] was employed for the ATRP. In addition, 10 vol % dimethylformamide was added for increased solubility of the catalyst complex in styrene. The system was homogeneous, except for the membrane, when the initiator/copper halide/ligand/monomer molar ratio was 1/1/3/500. As anticipated, the fastest polymerization rate of styrene was observed with the copper bromide/bpy-based catalyst system. The reaction rate was strongly temperature-dependent within the studied temperature interval of 100,130 °C. The degree of grafting increased linearly with time, thereby indicating first-order kinetics, regardless of the polymerization temperature. Furthermore, 120 °C was the maximum polymerization temperature that could be used in practice because the membrane structure was destroyed at higher temperatures. The degree of styrene grafting reached 400% after 3 h at 120 °C. Such a high degree of grafting could not be reached with conventional uncontrolled radiation-induced grafting methods because of termination reactions. On the basis of an Arrhenius plot, the activation energy for the homogeneous ATRP of styrene was 217 kJ/mol. The prepared membranes became proton-conducting after sulfonation of the polystyrene grafts. The highest conductivity measured for the prepared membranes was 70 mS/cm, which is comparable to the values normally measured for commercial Nafion membranes. The scanning electron microscopy/energy-dispersive X-ray results showed that the membranes had to be grafted through the matrix with both PVBC and polystyrene to become proton-conducting after sulfonation. In addition, PVDF- g -[PVBC- g -(styrene- block - tert -butyl acrylate)] membranes were also synthesized by ATRP. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 591,600, 2002; DOI 10.1002/pola.10146 [source] pEffects of UV radiation on the ultrastructure of several red algaePHYCOLOGICAL RESEARCH, Issue 1 2003Frank Poppe SUMMARY The effect of ultraviolet (UV) radiation on the ultrastructure of four red algae, the endemic Antarctic Palmaria decipiens (Reinsch) Ricker and Phycodrys austrogeorgica Skottsberg, the Arctic-cold temperate Palmaria palmata (Linnaeus) O. Kuntze and the cosmopolitan Bangia atropurpurea (Roth) C. Agardh was studied. All four species showed a formation of ,inside-out' vesicles from the chloroplast thylakoids upon exposure to artificial UV-radiation. In P. decipiens, most vesicles were developed after 8 h and in P. palmata, after 48 h of UV exposure. In B. atropurpurea, vesi-culation of thylakoids was observed after 72 h of UV irradiation. In Ph. austrogeorgica, the chloroplast envelope and thylakoid membranes were damaged and the phycobilisomes became detached from the thylakoids after 12 h of UV exposure. Ultraviolet-induced changes in the membrane structure of mitochondria were observed in P. decipiens and P. palmata. However, in P. decipiens they were reversible as was the damage in chloroplast fine structure after 12 h of UV treatment. Protein crystals in Ph. austrogeorgica showed degradation after exposure to UV radiation. Different methods of fixation and embedding macroalgal material are discussed. These findings give insight into the fine structural changes which occur during and after UV exposure and indicate a relationship between the species dependent sensitivity to UV-exposure and the depth distribution of the different species. [source] The relationship between changes in the cell wall, lipid peroxidation, proliferation, senescence and cell deathPHYSIOLOGIA PLANTARUM, Issue 1 2003Gerhard Spiteller Plants and mammals contain polyunsaturated fatty acids (PUFAs) in their membranes. PUFAs belong to the most oxygen sensitive molecules encountered in nature. It would seem that nature has selected this property of PUFAs for signalling purposes: PUFAs are stored in the surface of cells and organelles not in free form but conjugated to phospho- and galactolipids. Any change in membrane structure apparently activates membrane-bound phospholipases, which cleave the conjugates. The obtained free PUFAs are substrates for lipoxygenases (LOX). These transform PUFAs to lipidhydroperoxides (LOOHs). LOOHs are converted to a great variety of secondary products. These lipid-peroxidation (LPO) products and the resulting generated products thereof represent biological signals, which do not require a preceding activation of genes. They are produced as a non-specific response to a large variety of external or internal impacts, which therefore do not need interaction with specific receptors. When, due to an external impact, e.g. attack of a microorganism, or to a change in temperature, the amount of liberated free PUFAs exceeds a certain threshold, LOX commit suicide. Thus iron ions, located in the active centre of LOX, are liberated. Iron ions react with LOOHs in the close surroundings by generating alkoxy radicals (LO.). These induce a non-enzymatic LPO. A fraction of the LO. radicals generated from linoleic acid (LPO products derived from linoleic acid play a dominant role in signalling which was previously overlooked) is converted to 2,4-dienals which induce the programmed cell death (PCD) and the hypersensitive reaction (HR). While peroxyl radicals (LOO.) generated as intermediates in the course of an enzymatic LPO are transformed within the enzyme complex to corresponding anions (LOO,), and thus lose their reactivity, peroxyl radicals generated in non-enzymatic reactions are not deactivated. They not only react by abstraction of hydrogen atoms from activated X-H bonds of molecules in their close vicinity, but also by epoxidation of double bonds and oxidation of a variety of biological molecules, causing a dramatic change in molecular structure which finally leads to cell death. As long as reducing agents, like glutathione, or compounds with free phenolic groups are available, the amount of LOOHs is kept low. Cell death is induced in a defined way by apoptosis. But when the reducing agents have been consumed, PCD seems to switch to necrotic processes. Thus proliferation is induced by minor changes at the cell membrane, while slow changes at cell membranes are linked with apoptosis (e.g. response to attack of microorganisms or drought) and necrosis (severe wounding), depending only on the amount, but not on the type, of applied stimulus. [source] Organic,inorganic hybrid membranes prepared from the sol,gel process of poly(butyleneadipate- co -terephthalate) and TiO2POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2009Chien-Hong Lin Abstract Organic,inorganic hybrids based on poly(butyleneadipate- co -terephthalate)/titanium dioxide (PBAT/TiO2) hybrid membranes were prepared via a sol,gel process. The PBAT/TiO2 hybrid membranes were prepared for various PBAT/TiO2 ratios. The resulting hybrids were characterized with a morphological structure, hydrophilicity, biodegradability, and thermal properties. The results showed that macrovoids underwent a transition into a sponge-like membrane structure with the addition of TiO2. After sol,gel transition, a strong interaction between the inorganic network and polymeric chains led to an increase in glass transition temperature (Tg), thermal degrading temperature, and hydrophilicity, and hence a higher biodegradability. According to X-ray diffraction measurements of the crystal structure of the hybrid, the presence of TiO2 did not change the crystal structure of PBAT. TiO2 networks are uniformly dispersed into the PBAT matrix and no aggregation of TiO2 networks in the hybrid membranes was observed through the small angle X-ray scattering measurements. Thus, the sol,gel process of PBAT and TiO2 can be used to prepare a hybrid with higher application temperature and faster biodegradation rate. Copyright © 2008 John Wiley & Sons, Ltd. [source] The tegument surface membranes of the human blood parasite Schistosoma mansoni: A proteomic analysis after differential extractionPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 5 2006Simon Braschi Abstract The blood fluke Schistosoma mansoni can live for years in the hepatic portal system of its human host and so must possess very effective mechanisms of immune evasion. The key to understanding how these operate lies in defining the molecular organisation of the exposed parasite surface. The adult worm is covered by a syncytial tegument, bounded externally by a plasma membrane and overlain by a laminate secretion, the membranocalyx. In order to determine the protein composition of this surface, the membranes were detached using a freeze/thaw technique and enriched by sucrose density gradient centrifugation. The resulting preparation was sequentially extracted with three reagents of increasing solubilising power. The extracts were separated by 2-DE and their protein constituents were identified by MS/MS, yielding predominantly cytosolic, cytoskeletal and membrane-associated proteins, respectively. After extraction, the final pellet containing membrane-spanning proteins was processed by liquid chromatographic techniques before MS. Transporters for sugars, amino acids, ions and other solutes were found together with membrane enzymes and proteins concerned with membrane structure. The proteins identified were categorised by their function and putative location on the basis of their homology with annotated proteins in other organisms. [source] The evolution of coenzyme QBIOFACTORS, Issue 1-4 2008Frederick L. Crane In the 50 years since the identification of coenzyme Q as an electron carrier in mitochondria, it has been identified with diverse and unexpected functions in cells. Its discovery came as a result of a search for electron carriers in mitochondria following the identification of flavin and cytochromes by Warburg, Keilin, Chance and others. As a result of investigation of membrane lipids at D.E. Green's laboratory at University of Wisconsin coenzyme Q was identified as the electron carrier between primary flavoprotein dehydrogenases and the cytochromes. Then Peter Mitchell identified the role of transmembrane proton transfer as a basis for ATP synthesis. The general distribution of coenzyme Q in all cell membranes then led to the recognition of a role as a primary antioxidant. The protonophoric function was extended to acidification of Golgi and lysosomal vericles. A further role in proton release through the plasma membrane and its relation to cell proliferation has not been fully developed. A role in generation of H2 O2 as a messenger for hormone and cytokine action is indicated as well as prevention of apoptosis by inhibition of ceramide release. Identification of the genes and proteins required for coenzyme Q synthesis has led to a basis for defining deficiency. For 50 years Karl Folkers has led the search for deficiency and therapeutic application. The development of large scale production, better formulation for uptake, and better methods for analysis have furthered this search. The story isn't over yet. Questions remain about effects on membrane structure, breakdown and control of cellular synthesis and uptake and the basis for therapeutic action. [source] Affinity of polyphenols for lipid bilayersBIOFACTORS, Issue 1-4 2000Tsutomu Nakayama Abstract Interaction of tea catechins with lipid bilayers has been investigated with liposome systems. Epicatechin gallate had the highest affinity for lipid bilayers, followed by epigallocatechin gallate, epicatechin, and epigallocatechin. Epicatechin gallate and epigallocatechin gallate in the surface of lipid bilayer perturbed the membrane structure. [source] Chloride ATPase pumps in nature: do they exist?BIOLOGICAL REVIEWS, Issue 2 2003GEORGE A. GERENCSER ABSTRACT Five widely documented mechanisms for chloride transport across biological membranes are known: anioncoupled antiport, Na+ and H+ -coupled symport, Cl, channels and an electrochemical coupling process. These transport processes for chloride are either secondarily active or are driven by the electrochemical gradient for chloride. Until recently, the evidence in favour of a primary active transport mechanism for chloride has been inconclusive despite numerous reports of cellular Cl, -stimulated ATPases coexisting, in the same tissue, with uphill ATP-dependent chloride transport. Cl, -stimulated ATPase activity is a ubiquitous property of practically all cells with the major location being of mitochondrial origin. It also appears that plasma membranes are sites of Cl, -stimulated ATPase pump activity. Recent studies of Cl, -stimulated ATPase activity and ATP-dependent chloride transport in the same plasma membrane system, including liposomes, strongly suggest a mediation by the ATPase in the net movement of chloride up its electrochemical gradient across the plasma membrane structure. Contemporary evidence points to the existence of Cl, -ATPase pumps; however, these primary active transporters exist as either P-, F- or V-type ATPase pumps depending upon the tissue under study. [source] Mechanistic study of membrane concentration and recovery of Listeria monocytogenesBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2005Wan-Tzu Chen Abstract Detection of the foodborne pathogen Listeria monocytogenes requires that food samples be processed to remove proteins and lipids, concentrate microorganisms to a detectable concentration, and recover the concentrated cells in a small volume compatible with micron-scale biochips. Mechanistic considerations addressed in this research include the roles of membrane structure, pore size, and detergents in maximizing recovery of cells from a complex biological fluid. The fluid in this case was a food sample (hotdog extract) inoculated with L. monocytogenes. This study showed how membrane filtration using a syringe filter is able to concentrate L. monocytogenes by 95× with up to 95% recovery of living microorganisms by concentrating 50 mL of food sample into a volume of 500 ,L. Tween 20 was added to the sample to prevent irreversible adsorption of the microorganism to the membrane and thereby help to ensure high recovery. Comparison of polycarbonate, mixed cellulose, nylon, and PVDF membranes with 0.2 to 0.45 ,m pores showed the 0.2 ,m polycarbonate membrane with straight through, mono-radial pores gives the highest recovery of living microorganisms. The mixed cellulose, nylon, and PVDF membranes have a fibrous structure whose characteristic openings are much larger than their effective pore size cut-offs of 0.22 or 0.45 ,m. We define conditions for rapid membrane-based cell concentration and recovery that has the potential to supplant enrichment steps that require a day or more. This approach has the added benefit of facilitating examination of a large amount of fluid volume by reducing its volume to a range that is compatible with the microliter scales of biochip or other biosensor detection systems. © 2004 Wiley Periodicals, Inc. [source] Bacterial pathogens and the autophagic responseCELLULAR MICROBIOLOGY, Issue 1 2010María C. Lerena Summary The host cell recognition and removal of invading pathogens are crucial for the control of microbial infections. However, several microorganisms have developed mechanisms that allow them to survive and replicate intracellularly. Autophagy is an ubiquitous physiological pathway in eukaryotic cells, which maintains the cellular homeostasis and acts as a cell quality control mechanism to eliminate aged organelles and unnecessary structures. In addition, autophagy has an important role as a housekeeper since cells that have to get rid of invading pathogens use this pathway to assist this eradication. In this review we will summarize some strategies employed by bacterial pathogens to modulate autophagy to their own benefit and, on the other hand, the role of autophagy as a protective process of the host cell. In addition, we will discuss here recent studies that show the association of LC3 to a pathogen-containing compartment without a classical autophagic sequestering process (i.e. formation of a double membrane structure). [source] Pervaporative Dehydration of Alcohols by Carbonized Kapton® PolyimideCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2010A. Sungpet Abstract Kapton® polyimide was carbonized at 873, 1073 and 1273,K with a heating rate of 1, 3 and 5,K,min,1 and applied to the dehydration of methanol, ethanol and isopropanol by pervaporation. Lowering the heating rate or increasing the carbonization temperature resulted in higher selectivity and a decrease in permeability. X-ray diffraction data revealed that when carbonized at high temperature or with a low heating rate, the membrane had lower interplanar spacing, which corresponded to a reduction in pore size. It was also found that the carbonization temperature had a greater influence on the membrane structure than the heating rate. A comparison between permeability observed from single-component and bi-component feeds indicated that the separation mechanism involved more than molecular sieving alone. [source] Possible Molecular Evolution of Biomembranes: from Single-Chain to Double-Chain LipidsCHEMISTRY & BIODIVERSITY, Issue 5 2007Mari Gotoh Abstract We have studied a possible evolution process permitting a ,primitive' membrane to evolve towards a membrane structure with an outer wall, similar to that of bacteria. We have investigated whether a polysaccharide bearing hydrophobic phytyl or cholesteryl chains coats giant vesicles made of single- or double-chain lipids. Phytyl-pullulan 5b was found to bind to the surface of vesicles made of either single- or double-chain lipids. In contrast, cholesteryl-pullulan 5a only coated the surface of vesicles made of double-chain lipids. These results indicate that there must be a close match between the size and shape of membrane constituents and the hydrophobic molecules to be inserted. This process could, thus, provide a selection mechanism of lipid-membrane constituents during the course of biomembrane evolution. The presence of the above ,hydrophobized' polysaccharides on the surface of different giant vesicles was identified by lectin binding. Both concanavalin A and annexin V were shown by fluorescence microscopy to bind spontaneously to vesicles made of double-chain lipids. Our experiments exemplify that self-organization of amphiphiles into closed vesicles in aqueous solution automatically leads to the coating of vesicles by ,hydrophobized' polysaccharides, which then permit lectin binding. This is a possible mechanism for the evolution of primitive membranes towards ,proto-cells'. [source] Dynamics of bacterial cytoskeletal elementsCYTOSKELETON, Issue 11 2009Peter L. Graumann Abstract Bacterial cytoskeletal elements are involved in an astonishing spectrum of cellular functions, from cell shape determination to cell division, plasmid segregation, the positioning of membrane-associated proteins and membrane structures, and other aspects of bacterial physiology. Interestingly, these functions are not necessarily conserved, neither between different bacterial species nor between bacteria and eukaryotic cells. The flexibility of cytoskeletal elements in performing different tasks is amazing and emphasises their very early development during evolution. This review focuses on the dynamics of cytoskeletal elements from bacteria. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] Amperometric Glucose Biosensing of Gold Nanoparticles and Carbon Nanotube Multilayer MembranesELECTROANALYSIS, Issue 9 2007Ying Liu Abstract A novel multilayer gold nanoparticles/multiwalled carbon nanotubes/glucose oxidase membrane was prepared by electrostatic assembly using positively charged poly(dimethyldiallylammonium chloride) to connect them layer by layer. The modification process and membrane structures were characterized by atomic force microscopy, scanning electron microscopy and electrochemical methods. This membrane showed excellent electrocatalytic character for glucose biosensing at a relatively low potential (,0.2,V). The Km value of the immobilized glucose oxidase was 10.6,mM. This resulting sensor could detect glucose up to 9.0,mM with a detection limit of 128,,M and showed excellent analytical performance. [source] Computational form-finding of tension membrane structures,Non-finite element approaches: Part 1.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003Use of cubic splines in finding minimal surface membranes Abstract This paper, presented in three parts, discusses a computational methodology for form-finding of tension membrane structures (TMS), or fabric structures, used as roofing forms. The term ,form-finding' describes a process of finding the shape of a TMS under its initial tension. Such a shape is neither known a priori, nor can it be described by a simple mathematical function. The work is motivated by the need to provide an efficient numerical tool, which will allow a better integration of the design/analysis/manufacture of TMS. A particular category of structural forms is considered, known as minimal surface membranes (such as can be reproduced by soap films). The numerical method adopted throughout is dynamic relaxation (DR) with kinetic damping. Part 1 describes a new form-finding approach, based on the Laplace,Young equation and cubic spline fitting to give a full, piecewise, analytical description of a minimal surface. The advantages arising from the approach, particularly with regard to manufacture of cutting patterns for a membrane, are highlighted. Part 2 describes an alternative and novel form-finding approach, based on a constant tension field and faceted (triangular mesh) representation of the minimal surface. It presents techniques for controlling mesh distortion and discusses effects of mesh control on the accuracy and computational efficiency of the solution, as well as on the subsequent stages in design. Part 3 gives a comparison of the performance of the initial method (Part 1) and the faceted approximations (Part 2). Functional relations, which encapsulate the numerical efficiency of each method, are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Computational form-finding of tension membrane structures,Non-finite element approaches: Part 2.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003Triangular mesh discretization, control of mesh distortion in modelling minimal surface membranes Abstract This paper, presented in three parts, discusses a computational methodology for form-finding of tension membrane structures (TMS), or fabric structures, used as roofing forms. The term ,form-finding' describes a process of finding the shape of a TMS under its initial tension. Such a shape is neither known a priori, nor can it be described by a simple mathematical function. The work is motivated by the need to provide an efficient numerical tool, which will allow a better integration of the design/analysis/manufacture of TMS. A particular category of structural forms is considered, known as minimal surface membranes (such as can be reproduced by soap films). The numerical method adopted throughout is dynamic relaxation (DR) with kinetic damping. Part 1 gave a background to the problem of TMS design, described the DR method, and presented a new form-finding methodology, based on the Laplace,Young equation and cubic spline fitting to give a full, piecewise, analytical description of the surface. Part 2 describes an alternative and novel form-finding method, based on a constant tension field and faceted (triangular mesh) representation of the minimal surface. Techniques for controlling mesh distortion are presented, and their effects on the accuracy and computational efficiency of the solution, as well as on the subsequent stages in design, are examined. Part 3 gives a comparison of the performance of the initial method (Part 1) and the faceted approximations (Part 2). Functional relations, which encapsulate the numerical efficiency of each method, are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Numerical simulation of viscous flow interaction with an elastic membraneINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2008Lisa A. Matthews Abstract A numerical fluid,structure interaction model is developed for the analysis of viscous flow over elastic membrane structures. The Navier,Stokes equations are discretized on a moving body-fitted unstructured triangular grid using the finite volume method, taking into account grid non-orthogonality, and implementing the SIMPLE algorithm for pressure solution, power law implicit differencing and Rhie,Chow explicit mass flux interpolations. The membrane is discretized as a set of links that coincide with a subset of the fluid mesh edges. A new model is introduced to distribute local and global elastic effects to aid stability of the structure model and damping effects are also included. A pseudo-structural approach using a balance of mesh edge spring tensions and cell internal pressures controls the motion of fluid mesh nodes based on the displacements of the membrane. Following initial validation, the model is applied to the case of a two-dimensional membrane pinned at both ends at an angle of attack of 4° to the oncoming flow, at a Reynolds number based on the chord length of 4 × 103. A series of tests on membranes of different elastic stiffness investigates their unsteady movements over time. The membranes of higher elastic stiffness adopt a stable equilibrium shape, while the membrane of lowest elastic stiffness demonstrates unstable interactions between its inflated shape and the resulting unsteady wake. These unstable effects are shown to be significantly magnified by the flexible nature of the membrane compared with a rigid surface of the same average shape. Copyright © 2007 John Wiley & Sons, Ltd. [source] Discovery of the Porosome: revealing the molecular mechanism of secretion and membrane fusion in cellsJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 1 2004B. P. Jena Abstract Secretion and membrane fusion are fundamental cellular processes involved in the physiology of health and disease. Studies within the past decade reveal the molecular mechanism of secretion and membrane fusion in cells. Studies reveal that membrane-bound secretory vesicles dock and fuse at porosomes, which are specialized plasma membrane structures. Swelling of secretory vesicles result in a build-up of intravesicular pressure, which allows expulsion of vesicular contents. The discovery of the porosome, its isolation, its structure and dynamics at nm resolution and in real time, its biochemical composition and functional reconstitution, are discussed. The molecular mechanism of secretory vesicle fusion at the base of porosomes, and vesicle swelling, have been resolved. With these findings a new understanding of cell secretion has emerged and confirmed by a number of laboratories. [source] Narrow-band UVB-induced Externalization of Selected Nuclear Antigens in Keratinocytes: Implications for Lupus Erythematosus Pathogenesis,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009Adam Reich The aim of this study was to analyze whether sera obtained from patients with lupus erythematosus (LE) react with membrane structures found on keratinocytes irradiated with narrow-band ultraviolet B (NB-UVB). We applied atomic force microscopy (AFM) to visualize cell surface structures expressing nuclear antigens upon apoptosis following NB-UVB irradiation. Immortalized human keratinocytes (HaCaT) were cultured under standard conditions, irradiated with 800 mJ cm,2 NB-UVB light and imaged by AFM mounted on an inverted optical microscope. It was observed that NB-UVB irradiation provoked significant alterations of the keratinocyte morphology and led to the membrane expression of antigens recognized by anti-La and anti-Ro 60 kDa sera but not by antidouble-strand DNA sera. The presence of La and Ro 60 kDa antigens on keratinocyte surfaces after NB-UVB irradiation was limited mainly to the small bleb-like protrusions found on the keratinocytes by AFM. A closer investigation by AFM also revealed that some structures positively stained with anti-Ro 60 kDa serum were also located submembranously. We hypothesize that the externalization of some nuclear antigens because of NB-UVB exposure might be responsible for exacerbation of skin symptoms in patients suffering from LE. [source] Ultrastructure of the differentiating zygotospores of Porphyra leucosticta (Rhodophyta)PHYCOLOGICAL RESEARCH, Issue 4 2002Ioannes Tsekos SUMMARY The ultrastructure of zygotosporogenesis is described for the red alga Porphyra leucosticta Thuret. Packets of eight zygotosporangia, each packet derived from a single carpogonium are interspersed among vegetative cells. Zygotospore differentiation in Porphyra can be separated into three developmental stages. (i) Young zygotospores exhibit a nucleus and a large centrally located, lobed plastid with pyrenoid. Mucilage is produced within concentric membrane structures during their dilation, thus resulting in the formation of mucilage sacs. Subsequently, these sacs release their contents, initiating the zygotospore wall formation. Straight-profiled dictyosomes produce vesicles that also provide wall material. During the later stages of young zygotospores, starch polymerization commences, (ii) Medium-aged zygotospores are characterized by the presence of fibrous vacuoles. These are formed from the ,fibrous vacuole associated organelles'. The fibrous vacuoles finally discharge their contents. (iii) Mature zygotospores are recognized by the presence of numerous cored vesicles produced by dictyosomes. Cored vesicles either discharge their contents or are incorporated into the fibrous vacuoles. There is a gradual reduction of starch granules during zygotospore differentiation. Mature zygotospores are surrounded by a fibrous wall, have a large chloroplast with pyrenoid and well-depicted phycobilisomes but are devoid of starch granules. [source] Biochemical and molecular responses to water stress in resurrection plantsPHYSIOLOGIA PLANTARUM, Issue 2 2004Giovanni Bernacchia A small group of angiosperms, known as resurrection plants, can tolerate extreme dehydration. They survive in arid environments because they are able to dehydrate, remain quiescent during long periods of drought, and then resurrect upon rehydration. Dehydration induces the expression of a large number of transcripts in resurrection plants. Gene products with a putative protective function such as LEA proteins have been identified; they are expressed at high levels in the cytoplasm or in chloroplasts upon dehydration and/or ABA treatment of vegetative tissue. An increase in sugar concentration is usually observed at the onset of desiccation in vegetative tissue of resurrection plants. These sugars may be effective in osmotic adjustment or they may stabilize membrane structures and proteins. Regulatory genes such as a protein translation initiation factor, homeodomain-leucine zipper genes and a gene probably working as a regulatory RNA have been isolated and characterized. The knowledge of the biochemical and molecular responses that occur during the onset of drought may help to improve water stress tolerance in plants of agronomic importance. [source] Anchorage to the cytosolic face of the endoplasmic reticulum membrane: a new strategy to stabilize a cytosolic recombinant antigen in plantsPLANT BIOTECHNOLOGY JOURNAL, Issue 6 2008Alessandra Barbante Summary The levels of accumulation of recombinant vaccines in transgenic plants are protein specific and strongly influenced by the subcellular compartment of destination. The human immunodeficiency virus protein Nef (negative factor), a promising target for the development of an antiviral vaccine, is a cytosolic protein that accumulates to low levels in transgenic tobacco and is even more unstable when introduced into the secretory pathway, probably because of folding defects in the non-cytosolic environment. To improve Nef accumulation, a new strategy was developed to anchor the molecule to the cytosolic face of the endoplasmic reticulum (ER) membrane. For this purpose, the Nef sequence was fused to the C-terminal domain of mammalian ER cytochrome b5, a long-lived, tail-anchored (TA) protein. This consistently increased Nef accumulation by more than threefold in many independent transgenic tobacco plants. Real-time polymerase chain reaction of mRNA levels and protein pulse-chase analysis indicated that the increase was not caused by higher transcript levels but by enhanced protein stability. Subcellular fractionation and immunocytochemistry indicated that Nef-TA accumulated on the ER membrane. Over-expression of mammalian or plant ER cytochrome b5 caused the formation of stacked membrane structures, as observed previously in similar experiments performed in mammalian cells; however, Nef-TA did not alter membrane organization in tobacco cells. Finally, Nef could be removed in vitro by its tail-anchor, taking advantage of an engineered thrombin cleavage site. These results open up the way to use tail-anchors to improve foreign protein stability in the plant cytosol without perturbing cellular functions. [source] | |||||||||||||||||||||||||||||||||||||