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The role of target membrane sialic acid residues in the fusion activity of the influenza virus: the effect of two types of ganglioside on the kinetics of membrane merging

Ramalho-Santos, João; Lima, João Pedroso De
Fonte: Polish Society for Cell Biology Publicador: Polish Society for Cell Biology
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.146523%
The influenza virus enters target cells via the action of hemagglutinin proteins (HA) inserted into the viral envelope. HA promotes membrane fusion between the viral envelope and endosomal membrane at low pH, following viral binding to sialic acid-containing receptors on target cells, and internalization by endocytosis. The effect of target membrane sialic acid residues on the fusion activity of the influenza virus towards model membranes was evaluated by both reduction, (i.e. treating somatic cells with neuraminidase- (NA-) prior to virus-cell interactions), and by supplementing liposomes with the gangliosides GD1a and GT1b. The harshness of the neuraminidase pretreatment of target cells required to affect virus-induced membrane merging was found to greatly depend on the assay conditions, i.e. whether a virus-cell prebinding step at neutral pH was included prior to acidification. Minor concentrations of neuraminidase were found to greatly reduce virus fusion, but only in the absence of a prebinding step; they had no effect if this step was included. Although membrane merging was greatly reduced following cell neuraminidase pretreatment, virus-cell association at low pH was not disturbed proportionately. This probably reflects unspecific virus-cell binding under these conditions...

Kinetics and Thermodynamics of Interaction between Amphiphiles and Membranes: Interplay of Amphiphile Dipole Moment and Membrane Dipole Potential

Cardoso, Renato Manuel Soares
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
36.16414%
The passive permeation across biological membranes is a main route determining a drug bioavailability. However, the prediction of its permeability requires the quantitative knowledge of the kinetic parameters for interaction with the distinct membrane barriers (insertion, desorption and translocation). For most drugs this kinetic profile is unknown and their permeability rate is estimated based on their general hydrophobicity, accessed through partition between octanol and water. Considering that membranes are highly anisotropic systems, the comparison with homogenous phases is simpleminded. The orientation of the lipids in membranes, with their polar groups oriented to the aqueous phase and the non-polar hydrocarbon chains oriented towards the bilayer mid-plane, generates transversal gradients of polarity, density and charge. One important property that arises from this asymmetry is the dipole potential. Moreover, most drugs and biological ligands have an asymmetrical charge distribution, and the interplay between the amphiphile dipole moment and membrane potential is expected to play a important role in their interaction parameters. This question has however been overlooked by the scientific community. In this work we presented a detailed study of the kinetics and thermodynamics of the interaction between two fluorescent amphiphilic molecules...

Mitochondrial Swelling and Incipient Outer Membrane Rupture in Preapoptotic and Apoptotic Cells

Sesso, A.; Belizario, J. E.; Marques, M. M.; Higuchi, M. L.; Schumacher, R. I.; Colquhoun, A.; Ito, E.; Kawakami, J.
Fonte: WILEY-BLACKWELL; HOBOKEN Publicador: WILEY-BLACKWELL; HOBOKEN
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.17121%
Outer mitochondrial membrane (OMM) rupture was first noted in isolated mitochondria in which the inner mitochondrial membrane (IMM) had lost its selective permeability. This phenomenon referred to as mitochondrial permeability transition (MPT) refers to a permeabilized inner membrane that originates a large swelling in the mitochondrial matrix, which distends the outer membrane until it ruptures. Here, we have expanded previous electron microscopic observations that in apoptotic cells, OMM rupture is not caused by a membrane stretching promoted by a markedly swollen matrix. It is shown that the widths of the ruptured regions of the OMM vary from 6 to 250 nm. Independent of the perforation size, herniation of the mitochondrial matrix appeared to have resulted in pushing the IMM through the perforation. A large, long focal herniation of the mitochondrial matrix, covered with the IMM, was associated with a rupture of the OMM that was as small as 6 nm. Contextually, the collapse of the selective permeability of the IMM may precede or follow the release of the mitochondrial proteins of the intermembrane space into the cytoplasm. When the MPT is a late event, exit of the intermembrane space proteins to the cytoplasm is unimpeded and occurs through channels that transverse the outer membrane...

Efeito da membrana de Poli(vinilideno-trifluoretileno)/titanato de bário sobre a formação óssea em defeitos criados em calvárias de ratos; Effect of Poly(vinylidene-trifluoroethylene)/Barium Titanate Membrane on Bone Formation in Rat Calvaria Defects

Lopes, Helena Bacha
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/06/2014 PT
Relevância na Pesquisa
36.19606%
Os princípios biológicos da regeneração óssea guiada (ROG) têm contribuído para o desenvolvimento de membranas que, em odontologia, são utilizadas em diversas situações como tratamentos com implantes dentários, aumento de rebordo alveolar e reparo de defeitos ósseos de origem traumática e patológica. Resultados de experimentos in vitro comparando a membrana obtida pela associação do polímero poli(fluoreto de vinilideno-trifluoretileno) e da cerâmica titanato de bário (P(VDFTrFE)/ BT) à membrana de politetrafluoretileno (PTFE) mostraram uma resposta favorável de osteoblastos, fibroblastos e queratinócitos à membrana de P(VDFTrFE)/ BT. O objetivo do presente estudo foi avaliar o efeito da membrana de P(VDFTrFE)/ BT sobre a formação óssea in vivo. Foram criados defeitos ósseos com 5 mm de diâmetro em calvárias de ratos machos Wistar (peso 200-250 g), distribuídos em três grupos com relação à utilização ou não de membranas nos defeitos ósseos: (1) membrana de P(VDF-TrFE)/BT; (2) membrana de PTFE; (3) nenhum tipo de membrana. Ao final de 4 e 8 semanas os animais foram eutanasiados e as amostras foram submetidas à: (1) análise por microtomografia computadorizada (micro-CT) para avaliar volume ósseo...

Study of membrane ageing and grafting mechanisms using electron paramagnetic resonance

Oliveira, Fábio R. P.; Matos, Cristina T.; Moura, José J. G.; Portugal, Carla A. M.; Crespo, João G.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Artigo de Revista Científica
Publicado em //2011 ENG
Relevância na Pesquisa
36.156%
An important setback for a wider use of membrane processes in industry is fouling, caused by aggregation of biomolecules at membrane surface and pores. Two important approaches to reduce this effect are the use of chemical cleaning procedures and the functionalisation of the membrane surface. However, both processes may lead to membrane degradation and structure alteration due to free radical formation or radical interaction with membrane polymer chains. In this work, electron paramagnetic resonance (EPR) was used to evaluate and quantify radical formation in both chemical cleaning and membrane functionalisation by UV grafting, allowing for a better understanding of free radical formation processes and their influence on membrane characteristics. Studies under different cleaning and grafting conditions, such as, cleaning agent concentration and pH, light intensity and irradiation were also performed showing the potential of EPR as a technique for monitoring both procedures. The information provided by EPR may contribute significantly to the development of new cleaning strategies which minimise the effect of membrane ageing and to the implementation of new and more efficient grafting procedures

Study of membrane emulsification process as a pre-step for the microencapsulation of lipid compounds by spray drying

Candéa, Tatiana Vidal
Fonte: Faculdade de Ciências e Tecnologia Publicador: Faculdade de Ciências e Tecnologia
Tipo: Dissertação de Mestrado
Publicado em //2013 ENG
Relevância na Pesquisa
36.182883%
Dissertation presented to Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa for obtaining the master degree in Membrane Engineering; Food emulsions play an important role in product development and formulation, as well as to encapsulation of food additives. Conventional methods for emulsion production may present some drawbacks, such as the use of high shear stress, high energy demanding and polydisperse droplet size distribution. In this sense, membrane emulsification emerges as an alternative method to overcome all this issues and to produce fine and stable emulsions. Linseed oil has been widely studied in the last years, due to its nutritional composition, being the richest ω-3 vegetable source and for that reason it was used as the raw material for emulsion production. Premix and direct (cross flow) membrane emulsification were carried out using three different membrane materials: polissulphone, cellulose ester and α-alumina membrane. For premix membrane emulsification (PME) the variables transmembrane pressure, membrane material, surfactant type and membrane mean pore size were evaluated. The membrane mean pore size was the crucial factor to achieve emulsions by PME, once it was not possible to achieve stable emulsion with mean pore sizes lower than 0.8 μm. For direct membrane emulsification...

Electron paramagnetic resonance study of lipid and protein membrane components of erythrocytes oxidized with hydrogen peroxide

Mendanha,S.A.; Anjos,J.L.V.; Silva,A.H.M.; Alonso,A.
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2012 EN
Relevância na Pesquisa
36.156%
Electron paramagnetic resonance (EPR) spectroscopy of spin labels was used to monitor membrane dynamic changes in erythrocytes subjected to oxidative stress with hydrogen peroxide (H2O2). The lipid spin label, 5-doxyl stearic acid, responded to dramatic reductions in membrane fluidity, which was correlated with increases in the protein content of the membrane. Membrane rigidity, associated with the binding of hemoglobin (Hb) to the erythrocyte membrane, was also indicated by a spin-labeled maleimide, 5-MSL, covalently bound to the sulfhydryl groups of membrane proteins. At 2% hematocrit, these alterations in membrane occurred at very low concentrations of H2O2 (50 µM) after only 5 min of incubation at 37°C in azide phosphate buffer, pH 7.4. Lipid peroxidation, suggested by oxidative hemolysis and malondialdehyde formation, started at 300 µM H2O2 (for incubation of 3 h), which is a concentration about six times higher than those detected with the probes. Ascorbic acid and α-tocopherol protected the membrane against lipoperoxidation, but did not prevent the binding of proteins to the erythrocyte membrane. Moreover, the antioxidant (+)-catechin, which also failed to prevent the cross-linking of cytoskeletal proteins with Hb, was very effective in protecting erythrocyte ghosts from lipid peroxidation induced by the Fenton reaction. This study also showed that EPR spectroscopy can be useful to assess the molecular dynamics of red blood cell membranes in both the lipid and protein domains and examine oxidation processes in a system that is so vulnerable to oxidation.

The Membrane-binding Motif of the Chloroplast Signal Recognition Particle Receptor (cpFtsY) Regulates GTPase Activity*S⃞♦

Marty, Naomi J.; Rajalingam, Dakshinamurthy; Kight, Alicia D.; Lewis, Nathaniel E.; Fologea, Daniel; Kumar, Thallapuranam Krishnaswamy Suresh; Henry, Ralph L.; Goforth, Robyn L.
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em 29/05/2009 EN
Relevância na Pesquisa
36.16414%
The chloroplast signal recognition particle (cpSRP) and its receptor (cpFtsY) function in thylakoid biogenesis to target integral membrane proteins to thylakoids. Unlike cytosolic SRP receptors in eukaryotes, cpFtsY partitions between thylakoid membranes and the soluble stroma. Based on sequence alignments, a membrane-binding motif identified in Escherichia coli FtsY appears to be conserved in cpFtsY, yet whether the proposed motif is responsible for the membrane-binding function of cpFtsY has yet to be shown experimentally. Our studies show that a small N-terminal region in cpFtsY stabilizes a membrane interaction critical to cpFtsY function in cpSRP-dependent protein targeting. This membrane-binding motif is both necessary and sufficient to direct cpFtsY and fused passenger proteins to thylakoids. Our results demonstrate that the cpFtsY membrane-binding motif may be functionally replaced by the corresponding region from E. coli, confirming that the membrane-binding motif is conserved among organellar and prokaryotic homologs. Furthermore, the capacity of cpFtsY for lipid binding correlates with liposome-induced GTP hydrolysis stimulation. Mutations that debilitate the membrane-binding motif in cpFtsY result in higher rates of GTP hydrolysis...

The Intrinsically Disordered Nuclear Localization Signal and Phosphorylation Segments Distinguish the Membrane Affinity of Two Cytidylyltransferase Isoforms*

Dennis, Melissa K.; Taneva, Svetla G.; Cornell, Rosemary B.
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.16414%
Membrane phosphatidylcholine homeostasis is maintained in part by a sensing device in the key regulatory enzyme, CTP:phosphocholine cytidylyltransferase (CCT). CCT responds to decreases in membrane phosphatidylcholine content by reversible membrane binding and activation. Two prominent isoforms, CCTα and -β2, have nearly identical catalytic domains and very similar membrane binding amphipathic helical (M) domains but have divergent and structurally disordered N-terminal (N) and C-terminal phosphorylation (P) regions. We found that the binding affinity of purified CCTβ2 for anionic membranes was weaker than CCTα by more than an order of magnitude. Using chimeric CCTs, insertion/deletion mutants, and truncated CCTs, we show that the stronger affinity of CCTα can be attributed in large part to the electrostatic membrane binding function of the polybasic nuclear localization signal (NLS) motif, present in the unstructured N-terminal segment of CCTα but lacking in CCTβ2. The membrane partitioning of CCTβ2 in cells enriched with the lipid activator, oleic acid, was also weaker than that of CCTα and was elevated by incorporation of the NLS motif. Thus, the polybasic NLS can function as a secondary membrane binding motif not only in vitro but in the context of cell membranes. A comparison of phosphorylated...

Effect of Hydroperoxides on Red Blood Cell Membrane Mechanical Properties

Hale, John P.; Winlove, C. Peter; Petrov, Peter G.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 19/10/2011 EN
Relevância na Pesquisa
36.156%
We investigate the effect of oxidative stress on red blood cell membrane mechanical properties in vitro using detailed analysis of the membrane thermal fluctuation spectrum. Two different oxidants, the cytosol-soluble hydrogen peroxide and the membrane-soluble cumene hydroperoxide, are used, and their effects on the membrane bending elastic modulus, surface tension, strength of confinement due to the membrane skeleton, and 2D shear elastic modulus are measured. We find that both oxidants alter significantly the membrane elastic properties, but their effects differ qualitatively and quantitatively. While hydrogen peroxide mainly affects the elasticity of the membrane protein skeleton (increasing the membrane shear modulus), cumene hydroperoxide has an impact on both membrane skeleton and lipid bilayer mechanical properties, as can be seen from the increased values of the shear and bending elastic moduli. The biologically important implication of these results is that the effects of oxidative stress on the biophysical properties, and hence the physiological functions, of the cell membrane depend on the nature of the oxidative agent. Thermal fluctuation spectroscopy provides a means of characterizing these different effects, potentially in a clinical milieu.

The Properties of Chondrocyte Membrane Reservoirs and Their Role in Impact-Induced Cell Death

Moo, Eng Kuan; Amrein, Matthias; Epstein, Marcelo; Duvall, Mike; Abu Osman, Noor Azuan; Pingguan-Murphy, Belinda; Herzog, Walter
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 01/10/2013 EN
Relevância na Pesquisa
36.177407%
Impact loading of articular cartilage causes extensive chondrocyte death. Cell membranes have a limited elastic range of 3–4% strain but are protected from direct stretch during physiological loading by their membrane reservoir, an intricate pattern of membrane folds. Using a finite-element model, we suggested previously that access to the membrane reservoir is strain-rate-dependent and that during impact loading, the accessible membrane reservoir is drastically decreased, so that strains applied to chondrocytes are directly transferred to cell membranes, which fail when strains exceed 3–4%. However, experimental support for this proposal is lacking. The purpose of this study was to measure the accessible membrane reservoir size for different membrane strain rates using membrane tethering techniques with atomic force microscopy. We conducted atomic force spectroscopy on isolated chondrocytes (n = 87). A micron-sized cantilever was used to extract membrane tethers from cell surfaces at constant pulling rates. Membrane tethers could be identified as force plateaus in the resulting force-displacement curves. Six pulling rates were tested (1, 5, 10, 20, 40, and 80 μm/s). The size of the membrane reservoir, represented by the membrane tether surface areas...

Mechanisms of Membrane Disruption by Viral Entry Proteins

Kim, Irene
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
Relevância na Pesquisa
36.16414%
To enter and infect cells, viruses must overcome the barrier presented by the cell membrane. Enveloped viruses, which possess their own lipid bilayer, fuse their viral membrane with the cell membrane. Non-enveloped viruses, whose outer surface is composed of proteins, penetrate through the hydrophobic interior of the cell membrane. Viruses accomplish the processes by coupling conformational changes in viral "entry proteins" to membrane disruption. This dissertation investigates the membrane disruption mechanisms of rotavirus, a non-enveloped virus, and vesicular stomatitis virus (VSV), an enveloped virus. Rotavirus uses proteins of its outer capsid to penetrate the membrane and deliver a transcriptionally-active core particle into the cell cytoplasm. (VP5^*), an outer capsid protein, undergoes a foldback rearrangement that translocates three clustered hydrophobic loops by (sim 180^{circ}). This rearrangement resembles the foldback rearrangements of enveloped virus fusion proteins. In the first half of my dissertation, I show that the hydrophobicity of the (VP5^*) apex is required for membrane disruption during rotavirus cell entry by mutating hydrophobic residues within the loop to hydrophilic residues. One particular mutation diminishes liposome interaction by the protein...

A functional assessment of the sperm membrane: a multi-species approach

Murphy, Craig
Fonte: University of Limerick Publicador: University of Limerick
Tipo: info:eu-repo/semantics/doctoralThesis; all_ul_research; ul_published_reviewed; ul_theses_dissertations
ENG
Relevância na Pesquisa
36.192124%
peer-reviewed; A functional sperm membrane is essential for many of the processes which lead to the fertilisation of an oocyte, but this membrane is susceptible to oxidative damage with increasing duration of storage in liquid semen or during the cryopreservation process. The objectives of this thesis were to examine the effects of storage temperature, catalase supplementation and sperm number on the membrane function of liquid stored bull semen, sperm membrane protein profile on the membrane integrity of liquid stored boar semen and stabilisation of the stallion sperm membrane using cholesterol, prior to cryopreservation, on the membrane function of frozen-thawed stallion semen. Sperm progressive motility was assessed by microscopy, glucose consumption and total antioxidant capacity were assessed using commercial kits, and viability, oxidative stress, mitochondrial activity, acrosomal status and membrane fluidity were assessed by flow cytometry. Conception rates in dairy cows were assessed as the 60 day non-return rate in a field study assessing the effects of lowering the sperm number in liquid bull semen, which included a frozen-thawed semen treatment. In liquid bull semen, storage at temperatures above 22 °C had reduced motility and membrane integrity (P < 0.05)...

Close allies in membrane protein research: cell-free synthesis and nanotechnology

Shadiac, N.; Nagarajan, Y.; Waters, S.; Hrmova, M.
Fonte: Taylor & Francis Ltd Publicador: Taylor & Francis Ltd
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
36.16414%
Membrane proteins control fundamental processes that are inherent to nearly all forms of life such as transport of molecules, catalysis, signaling, vesicle fusion, sensing of chemical and physical stimuli from the environment, and cell-cell interactions. Membrane proteins are harbored within a non-equilibrium fluid-like environment of biological membranes that separate cellular and non-cellular environments, as well as in compartmentalized cellular organelles. One of the classes of membrane proteins that will be specifically treated in this article are transport proteins of plant origin, that facilitate material and energy transfer at the membrane boundaries. These proteins import essential nutrients, export cellular metabolites, maintain ionic and osmotic equilibriums and mediate signal transduction. The aim of this article is to report on the progress of membrane protein functional and structural relationships, with a focus on producing stable and functional proteins suitable for structural and biophysical studies. We interlink membrane protein production primarily through wheat-germ cell-free protein synthesis (WG-CFPS) with the growing repertoire of membrane mimicking environments in the form of lipids, surfactants, amphipathic surfactant polymers...

Dinuclear polypyridylruthenium(II) complexes: Flow cytometry studies of their accumulation in bacteria and the effect on the bacterial membrane

Li, F.; Feterl, M.; Warner, J.; Keene, F.; Collins, J.
Fonte: Oxford Univ Press Publicador: Oxford Univ Press
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
36.156%
Objectives To determine the energy dependency of and the contribution of the membrane potential to the cellular accumulation of the dinuclear complexes [{Ru(phen)₂}₂{μ-bbn}]⁵+ (Rubbn) and the mononuclear complexes [Ru(Me₄phen)₃]²+ and [Ru(phen)₂(bb₇)]²+ in Staphylococcus aureus and Escherichia coli, and to examine their effect on the bacterial membrane. Methods The accumulation of the ruthenium complexes in bacteria was determined using flow cytometry at a range of temperatures. The cellular accumulation of the ruthenium complexes was also determined in cells that had been incubated with the metal complexes in the presence or absence of metabolic stimulators or inhibitors and/or commercial dyes to determine the membrane potential or membrane permeability. Results The accumulation of ruthenium complexes in the two bacterial strains was shown to increase with increasing incubation temperature, with the relative increase in accumulation greater with E. coli, particularly for Rubb₁₂ and Rubb₁₆. No decrease in accumulation was observed for Rubb₁₂ in ATP-inhibited cells. While carbonyl cyanide m-chlorophenyl hydrazone (CCCP) did depolarize the cell membrane, no reduction in the accumulation of Rubb₁₂ was observed; however...

Investigations into the Plasma Membrane Trafficking of Multidrug Resistance Protein 4 (ABCC4/MRP4)

Miah, Mohammad Fahad
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.16414%
Multidrug resistance protein 4 (MRP4) is a member of subfamily C of the ATP-binding cassette superfamily of membrane transport proteins. In polarized cells, MRP4 localizes to the apical or basolateral plasma membrane depending on the tissue type. To gain insight into mechanisms regulating MRP4 plasma membrane trafficking, its interactions with the PDZ domain-containing CortBP1, a member of Shank2 family of adapter proteins, were investigated. Since CortBP1 is known to recruit proteins involved in endocytosis, it was hypothesized that CortBP1 plays a role in MRP4 internalization from the plasma membrane. Ectopic expression of CortBP1 led to decreased total MRP4 levels in HEK293T cells and cell surface biotinylation experiments and confocal microscopy showed that this decrease was at the plasma membrane. Pull-down experiments indicated that the interaction between CortBP1 and MRP4 requires the last four amino acids 1322ETAL of the transporter. They also suggested that MRP4 may exist in a complex with CortBP1 and endocytic proteins. In SH-SY5Y and BE(2)-C human neuroblastoma cells, RNAi-mediated knockdown of endogenous SHANK2 isoforms (including CORTBP1) resulted in increased total MRP4 levels. Confocal microscopy of SHANK2-depleted BE(2)-C cells suggested that this increase occurred at the plasma membrane. These observations demonstrate that the internalization of plasma membrane MRP4 is regulated by CortBP1...

Membrane Transport of Singlet Oxygen Monitored by Dipole Potential Measurements

Sokolov, Valerij S.; Pohl, Peter
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.156%
The efficiency of photodynamic reactions depends on 1), the penetration depth of the photosensitizer into the membrane and 2), the sidedness of the target. Molecules which are susceptible to singlet oxygen (1O2) experience less damage when separated from the photosensitizer by the membrane. Since 1O2 lifetime in the membrane environment is orders of magnitude longer than the time required for nonexcited oxygen (O2) to cross the membrane, this observation suggests that differences between the permeabilities or membrane partition of 1O2 and O2 exist. We investigated this hypothesis by releasing 1O2 at one side of a planar membrane while monitoring the kinetics of target damage at the opposite side of the same membrane. Damage to the target, represented by dipole-modifying molecules (phloretin or phlorizin), was indicated by changes in the interleaflet dipole potential difference Δϕb. A simple analytical model allowed estimation of the 1O2 interleaflet concentration difference from the rate at which Δϕb changed. It confirmed that the lower limit of 1O2 permeability is ∼2 cm/s; i.e., it roughly matches O2 permeability as predicted by Overton's rule. Consequently, the membrane cannot act as a barrier to 1O2 diffusion. Differences in the reaction rates at the cytoplasmic and extracellular membrane leaflets may be attributed only to 1O2 quenchers inside the membrane.

Novel Ceramic Membranes for Membrane Distillation: Surface Modification, Performance Comparison with PTFE Membranes, and Treatment of Municipal Wastewater

Hendren, Zachary Doubrava
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2011
Relevância na Pesquisa
36.17121%

Current global water scarcity and the spectre of a future critical shortage are driving the need for novel and energy saving water technology approaches. Desalination of seawater and the reuse of treated wastewater effluent, which have historically been viewed as undesirable water sources, are increasingly being explored as sources for reducing water consumption. Although the dominant technologies for taking these water sources to potable quality, energy consumption still makes them unsustainable for widespread application. Membrane distillation (MD) is an innovative water purification method that has shown promise as a technology that can address several of these issues. MD is a membrane process that produces very high quality product water. However, similarly to other thermal desalting processes, MD utilizes heat as the dominant source of energy rather than pressure, and can potentially be used to produce water at higher recoveries (and therefore less waste) than is feasible with existing approaches. Another important advantage of MD is that the water separation occurs at modest temperatures (<90oC), opening the door for the utilization of currently usable waste heat sources. Despite these advantages, MD is primarily a lab scale technology...

Image Cross Correlation Spectroscopy Used To Study the Membrane Localization of BMPRIa and FGF1

D'Angelo, Alex
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.16414%
Anja G. Nohe; Bone morphogenetic protein 2 (BMP2) and fibroblast growth factor 1 (FGF1) are known regulators of osteoblast proliferation and bone growth. BPM2 is known to induce differentiation of osteoblasts from mesenchymal stem cell precursors. Signaling which controls this process is initiated by the binding of BMP2 to BMP receptor type Ia (BMPRIa), initiating the dissociation of the BMPRIa associated protein casein kinase II (CK2) at one of three binding sites. Selective blocking of CK2 association with specially designed CK2 blocking peptides (CK2.1, CK2.2, CK2.3) has led to both osteoblast and adipocyte differentiation, the balance of which is altered in the disease osteoporosis. BMP receptor signaling has been found to be dependent upon receptor relocalization and aggregation on the plasma membrane, with the membrane domain caveolae playing a particularly important, though poorly understood role. These dynamics differ in cells isolated from mice of varying bone mineral density. FGF1 is another regulator of bone growth. Studies have shown that FGF1 readily induces new bone formation and can prevent bone loss in an induced osteoporotic rat model. FGF1 is released under stressed conditions via a membrane associated complex and transported across the plasma membrane by the poorly understood nonclassical transport mechanism...

Modification of the Pet-Membrane/Solution Interface: Effect on Electrical Parameters

Benavente,J.; Lara,R. de
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 EN
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36.16414%
Electrochemical characterization of a symmetric track-etched polyethylenthereftalate (PET) membrane in contact with KCl solutions at different concentrations was carried out by measuring impedance spectroscopy (IS) and membrane potential (MP), which allow the estimation of membrane electrical resistance and ion transport numbers, respectively. IS measurements permit us the characterization of membranes in "working conditions" (in contact with electrolyte solutions) and the determination of electrical parameters for the membrane and the membrane/solution interface (resistance, capacitance and Warburg impedance) by analyzing the impedance plots and using equivalent circuits as models. The non-reproducibility of membrane potential values for two series of measurements and the asymmetry of the impedance curves show the modification of the membrane/aqueous solution interface. This point was confirmed by the time evolution of the membrane system electrical resistance and the increase of nitrogen content obtained from X-ray photoelectron spectroscopy (XPS) analysis for dry and PET samples maintained in water for different periods of time, and the results indicate an increase in nitrogen content, which is attributed to bacterial presence on the membrane surfaces. These results seem to indicate modification of the PET-membrane/solution interface due to fouling and the possibility of its determination by electrical measurements.