Permeability of the cell walls

The effects of ultrasound upon the permeability of the cell walls of the gram-negative bacteria Pseudomonas aeruginosa toward hydrophobic compounds particularly antibiotics have been examined [8]. The penetration and distribution of 16-dosylstearic acid (16-DS) in the cell membranes of the bacteria was quantified by a spin-labeling electron spin resonance (ESR) method. The results indicated that the intracellular concentration of 16- D S was higher in insonated cells and increased linearly with the sonication power. 

The use of yeast cells as a eukaryotic complement to the Ames test led to the development of several protocols for the detection of mutation, gene conversion and recombination. The formal introduction of methods [23] followed by much development work from Zimmermarm s laboratory led to large systematic studies [24, 25] and OECD guidelines for the test battery (OECD 480, 481). However the assays are now rarely used, at least in part because of concerns over low sensitivity, thought to reflect limited permeability of the cell wall. 

Later, it was found that alkaline phosphatase was also released by osmotic shock E. coli were exposed to 0.5 M sucrose containing dilute tris-HCl buffer and EDTA, and then the centrifuged cells were rapidly dispersed in the shock medium of cold water or cold 5 X 10 4 M MgCl2. Although the cells were 80% viable with the latter case, almost all of the enzyme was released (9, 10). Other evidence indicates that the only important structural effect of EDTA is to increase the permeability of the cell wall (11, 12). Escherichia coli grow normally in the... 

In comparison with the penicillin and cephalosporin derivatives, the peptide antibiotics are not numbered among the major antibiotics . Their action mechanisms vary, e.g. inhibition of cell-wall synthesis, increased permeability of the cell wall, or influence on nucleic acid synthesis. 

During tea mannfacture, the plucked fresh tea leaves are first subjected to withering. The water permeability of the cell wall and membrane increases as the tea leaves keep losing water with concurrent increase of hydrolysis activity. The amount of theanine and glntamine is reduced due to hydrolysis, so that the amount of glutamate is greatly increased and the GAD activity is induced. Therefore, further anaerobic treatment resnlts in the accumulation of GABA in tea leaves. ... 

This latter observation correlates with the observation that (129) is a precursor for lomofungin (130) in Streptomyces lomodensis. It seems clear from the combined evidence that phenazine-1,6-dicarboxylic acid (129) is a precursor for all microbial phenazines. Failure to observe incorporation of (129) in Pseudomonas, with (by contrast) positive results in actinomycetes, may be attributed to differences in permeability of the cell walls cf. ref. 127). 

The peptidic nature of penicillin was not recognized immediately after its isolation. In its jS-lactam bicyclic ring structure the tripeptide -(L-a-aminoadipoyl)-L-cysteinyl-D-valine is hidden but in 1960 it was discovered in extracts of Penicillium by Arnstein et al. [11]. Experiments on biosynthesis of penicillins in the intact mycelium of the producing fungi did not lead to unequivocal results, due to the poor permeability of the cell wall. Protoplasts, naked cells obtained after enzymatic removal of the outer wall, however, were able to serve in studies with radioactively labeled potential precursors, and in cell-free systems from Cephalosporium acremonium, the route to isopenicillin N was finally revealed [12]. The tripeptide L-a-aminoadipoyl-L-cysteinyl-D-valine first forms the j -lactam moiety and a second, oxidative step closes the thiazolidine ring between the -carbon of valine and the thiol of cysteine (Fig. 9). 

Schemes of electron transfer interactions of FNR in thylakoid membranes are deduced mainly from experimental results obtained in model systems (reviewed in 1). Pioneering works by Bouges-Bocquet (4), who studied flash-induced transient of FNR in algal cells, has not tDeen followed by systematic investigations in isolated chloroplasts and thylakoid membranes. In algal cells, ambiguity arises from intense light scattering (5). Low permeability of the cell wall also restricts the use of inhibitors, ionophores, artificial acceptors and substrates. It is consequently necessary to confirm and extend these earlier studies using isolated thylakoid membranes and/or subchloroplast particles.

Lichen substances affect the permeability of the cell walls of the phycobionts, and could play an important role in symbiotic equilibrium (FoUmann and Villagran 1965 Kinrade... 

Primary irritants cause inflammation. Inflammation is one of the body s defence mechanisms. It is the reaction of a tissue to harm which is insufficient to kill the tissue and is typified by constriction of the small vessels in the affected area, dilation of the blood vessels, increased permeability of the vessel walls, and migration of the white blood and other defensive cells to the invading harmful chemical. The aim is to concentrate water and protein in the affected area to dilute the effect and wash away the chemical. Production of new cells is speeded up and contaminated surface cells are shed. 

SEM observations of acetylated wood have also shown that at WPGs in the region of 20 %, expansion of the cell wall into the lumen occurs (Evans etal., 2000 Mohebby and Militz, 2002 Sander etal., 2003). The decrease in lumen cross-sectional area may be related to the observation by Kumar etal. (1979) that the axial permeability of acetylated... 

Evidence of a role of lipid peroxidation in the cellular toxicity of ozone has been obtained in in vitro studies in which human red cells were exposed to this oxidant gas. The possibility that lipid peroxidation is responsible for altered permeability of bacterial cell walls after ozone exposure was proposed by Scott and Lesher and has since been con-... 

In order to cross the endothelial cell barrier, the macromolecules or drug-targeting complex must leave the circulation by either intercellular junctions or a mechanism similar to tnmscytosis. The permeability of the vessel wall could be... 

The normal structure of the cell wall is broken by pits. Changes appear already in the growth period of the cell. For instance, early stages of pit formation in softwoods are visible in the primary wall just before the cell reaches its final dimensions (primary pit fields). The microfibril network is loosened and new microfibrils are oriented around these points. The structure in the middle of the circles is tightened and the radially oriented microfibril bundles finally form a netlike membrane, permeable to liquids (margo) (Fig. 1-17). The central, thickened portion of the pit membrane... 

Physical disruption of the cell or change in permeability. The cell is a heterogeneous structure. Removal of any clement in that wall, or of the binding material, results in a breaching of the wall. Total destruction of the cell wall isn t necessary, ( rude trypsin, combined with lysozyme and lysoleeithin, is reported to lyse E. coli and Shigel1 <1 flexnev (63). 

The resistance to diffusion of a molecular species across a barrier equals the reciprocal of its permeability coefficient (Chapter 1, Section 1.4B). In this regard, we will let f COi be the permeability coefficient for CO2 diffusion across barrier j. To express the resistance of a particular mesophyll or chlo-roplast component on a leaf area basis, we must also incorporate Am sIA to allow for the actual area available for diffusion—the large internal leaf area acts like more pathways in parallel and thus reduces the effective resistance (Fig. 8-4). Because the area of the plasma membrane is about the same as that of the cell wall, and the chloroplasts generally occupy a single layer around the periphery of the cytosol (Figs. 1-1 and 8-11), the factor AmesIA applies to all of the diffusion steps of CO2 in mesophyll cells (all five individual resistances in Eq. 8.21). In other words, we are imagining for simplicity that the cell wall, the plasma membrane, the cytosol, and the chloroplasts are all in layers having essentially equal areas (Fig. 8-11). Thus, the resistance of any of the mesophyll or chloroplast components for CO2 diffusion,, is reduced from 1 /P co, by the reciprocal of the same factor, Ames/A ... 

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