Membrane Permeability: 100 Years Since Ernest Overton: 48 (Current Topics in Membranes)
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Analysis of mutant 2B proteins showed that both a cationic amphipathic alpha-helix and a second hydrophobic domain in 2B were required for these activities. Consistent with a presumed ability of protein 2B to increase membrane permeability , viruses carrying a mutant 2B protein exhibited a defect in virus release. Biomass properties and permeability in an immersed hollow fibre membrane bioreactor at high sludge concentrations.
Membrane Permeability: 100 Years Since Ernest Overton (eBook)
This study aimed to investigate the influence of biomass properties and high mixed liquor suspended solids MLSS concentrations on membrane permeability in a pilot-scale hollow fibre membrane bioreactor treating domestic wastewater. Various physicochemical and biological biomass parameters were measured throughout the trial, comprising pre-thickening, thickening and post-thickening periods with reference to the sludge concentration and with aerobic biotreatment continuing throughout. Correlations between dynamic changes in biomass characteristics and membrane permeability decline as well as permeability recovery were further assessed by statistical analyses.
Results showed the MLSS concentration to exert the greatest influence on sustainable membrane permeability , with a weaker correlation with particle size distribution.
The strong dependence of absolute recovered permeability on wet accumulated solids WACS concentration, or clogging propensity, revealed clogging to deleteriously affect membrane permeability decline and recovery from mechanical declogging and chemical cleaning , with WACS levels increasing with increasing MLSS. Evidence from the study indicated clogging may permanently reduce membrane permeability post declogging and chemical cleaning, corroborating previously reported findings.
Composite membranes are characterized by Raman spectroscopy, optical microscopy, X-ray diffraction, electrical measurements and gas permeability measurements. The enhancement in permeability is explained on the basis of well aligned easy channel provided by MWCNT in electrically aligned sample. The effect of thickness of membrane on the gas permeability also studied and thickness of about 30microm found to be optimum thickness for fast hydrogen gas permeates. Purohit, Vishnudutt; Bode, J. Alcohol exposure can promote the growth of Gram negative bacteria in the intestine which may result in accumulation of endotoxin.
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In addition, alcohol metabolism by Gram negative bacteria and intestinal epithelial cells can result in accumulation of acetaldehyde, which in turn can increase intestinal permeability to endotoxin by increasing tyrosine phosphorylation of tight junction and adherens junction proteins.
Alcohol-induced generation of nitric oxide may also contribute to increased permeability to endotoxin by reacting with tubulin, which may cause damage to microtubule cytoskeleton and subsequent disruption of intestinal barrier function. Increased intestinal permeability can lead to increased transfer of endotoxin from the intestine to the liver and general circulation where endotoxin may trigger inflammatory changes in the liver and other organs.
Alcohol may also increase intestinal permeability to peptidoglycan which can initiate inflammatory response in liver and other organs. In addition, acute alcohol exposure may potentiate the effect of burn injury on intestinal bacterial growth and permeability. Decreasing the number of Gram negative bacteria in the intestine can result in decreased production of endotoxin as well as acetaldehyde which is expected to decrease intestinal permeability to endotoxin.
In addition, intestinal permeability may be preserved by administering epidermal growth factor, L-glutamine, oats supplementation, or zinc thereby preventing the transfer of endotoxin to the general circulation. Thus reducing the number of intestinal Gram negative bacteria and. Permeability modes in fluctuating lipid membranes with DNA-translocating pores.
Membrane pores can significantly alter not only the permeation dynamics of biological membranes but also their elasticity. Large membrane pores able to transport macromolecular contents represent an interesting model to test theoretical predictions that assign active-like non-equilibrium behavior to the permeability contributions to the enhanced membrane fluctuations existing in permeable membranes [Maneville et al.
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Such high-amplitude active contributions arise from the forced transport of solvent and solutes through the open pores, which becomes even dominant at large permeability. In this paper, we present a detailed experimental analysis of the active shape fluctuations that appear in highly permeable lipid vesicles with large macromolecular pores inserted in the lipid membrane , which are a consequence of transport permeability events occurred in an osmotic gradient.
The experimental results are found in quantitative agreement with theory, showing a remarkable dependence with the density of membrane pores and giving account of mechanical compliances and permeability rates that are compatible with the large size of the membrane pore considered.
The presence of individual permeation events has been detected in the fluctuation time-series, from which a stochastic distribution of the permeation events compatible with a shot-noise has been deduced. The non-equilibrium character of the membrane fluctuations in a permeation field, even if the membrane pores are mere passive transporters, is clearly demonstrated.
Finally, a bio-nano-technology outlook of the proposed synthetic concept is given on the context of prospective uses as active membrane DNA-pores exploitable in gen-delivery applications based on lipid vesicles. Interaction of multiple biomimetic antimicrobial polymers with model bacterial membranes. Baul, Upayan, E-mail: upayanb imsc. Using atomistic molecular dynamics simulations, interaction of multiple synthetic random copolymers based on methacrylates on prototypical bacterial membranes is investigated.
The simulations show that the cationic polymers form a micellar aggregate in water phase and the aggregate, when interacting with the bacterial membrane , induces clustering of oppositely charged anionic lipid molecules to form clusters and enhances ordering of lipid chains. The model bacterial membrane , consequently, develops lateral inhomogeneity in membrane thickness profile compared to polymer-free system.
Study of the internal morphology of cation-exchange membranes by means of electroosmotic permeability relaxations. The effect of an ac sinusoidal perturbation of known amplitude and frequency superimposed to the usual dc applied electric voltage difference on the electroosmotic flow through three cation-exchange membranes with different morphology has been studied.
A dispersion of the electroosmotic permeability on the frequency of the applied ac signal has been found for the three membranes investigated, observing that the electroosmotic permeability reaches maximum values for some characteristic values of the frequency. These characteristic frequency values, which are related to relaxation processes in heterogeneous media, depend on the membrane system and permit to obtain information about the different structures of the membrane system. Thus, the study of the electroosmotic permeability relaxation can be used as a method to study the internal morphology of a cation-exchange membrane in a given electrolyte medium.
While adsorbed oligomers produced little or no significant membrane structural damage, increased membrane permeabilization to ionic species is understood in terms of enlarged membrane -inserted oligomers. Taken together, our results suggest that membrane -inserted oligomers are the primary species responsible for membrane permeability. Permeability of membranes to amino acids and modified amino acids: mechanisms involved in translocation. Chakrabarti, A. Principal Investigator ; Miller, S.
Principal Investigator. The amino acid permeability of membranes is of interest because they are one of the key solutes involved in cell function.
Membrane permeability coefficients P for amino acid classes, including neutral, polar, hydrophobic, and charged species, have been measured and compared using a variety of techniques. Decreasing lipid chain length increased permeability slightly 5-fold , while variations in pH had only minor effects on the permeability coefficients of the amino acids tested in liposomes.
Increasing the membrane surface charge increased the permeability of amino acids of the opposite charge, while increasing the cholesterol content decreased membrane permeability. The permeability coefficients for most amino acids tested were surprisingly similar to those previously measured for monovalent cations such as sodium and potassium approximately 10 cm s This observation suggests that the permeation rates for the neutral, polar and charged amino acids are controlled by bilayer fluctuations and transient defects, rather than partition coefficients and Born energy barriers.
Hydrophobic amino acids were 10 2 more permeable than the hydrophilic forms, reflecting their increased partition coefficient values.
External pH had dramatic effects on the permeation rates for the modified amino acid lysine methyl ester in response to transmembrane pH gradients. It was also shown that charge distributions dramatically alter permeation rates for modified di-peptides. These results may relate to the movement of peptides through membranes during protein translocation and to the origin of cellular membrane transport on the early Earth. Cholesterol is widely known to alter the physical properties and permeability of membranes. Several prior works have implicated cell membrane cholesterol as a barrier to tissue oxygenation, yet a good deal remains to be explained with regard to the mechanism and magnitude of the effect.
We use molecular dynamics simulations to provide atomic-resolution insight into the influence of cholesterol on oxygen diffusion across and within the membrane. Our simulations show strong overall agreement with published experimental data, reproducing the shapes of experimental oximetry curves with high accuracy.
These reductions in permeability can only be biologically consequential in contexts where the diffusional path of oxygen is not water dominated.
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In our simulations, cholesterol reduces the overall solubility of oxygen within the membrane but enhances the oxygen transport parameter solubility-diffusion product near the membrane center. Given relatively low barriers to passing from membrane to membrane , our findings support hydrophobic channeling within membranes as a means of cellular and tissue-level oxygen transport. In such a membrane -dominated diffusional scheme, the influence of cholesterol on oxygen permeability is large enough to warrant further attention.
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Published by Elsevier Inc. Permeability of C2C12 myotube membranes is influenced by stretch velocity. Mechanical signals are critical to the growth and maintenance of skeletal muscle, but the mechanism by which these signals are transduced by the cell remains unknown. This work examined the hypothesis that stretch conditions influence membrane permeability consistent with a role for membrane permeability in mechanotransduction.
C2C12 myotubes were grown in conditions that encourage uniform alignment and subjected to uniform mechanical deformation in the presence of fluorescein labeled dextran to evaluate membrane permeability as a function of stretch amplitude and velocity. Within a physiologically relevant range of conditions, a complex interaction between the two aspects of stretch was observed, with velocity contributing most strongly at large stretch amplitudes.
This suggests that membrane viscosity could contribute to mechanotransduction.