Relationship between gramacidin conformation dependent induction of phospholipid transbilayer movement and hexagonal HII phase formation in erythrocyte membranes

Addition of gramicidin in sufficient concentration from dimethylsulfoxide or trifluoroethanol to isolated erythrocyte membranes induces hexagonal HII phase formation for the phospholipids. In contrast, addition from ethanol does not change the overall bilayer organization despite a similar extent of peptide incorporation. The same solvent dependence is observed for the enhancement of transbilayer reorientation of lysophospholipids and unspecific leak formation in intact erythrocytes at lower gramicidin concentrations. These results indicate that the (β6.3) conformation of the peptide is essential for all three membrane perturbing effects

Fragility of the permeability barrier of Escherichia coli

An unsaturated fatty acid requiring auxotroph of Escherichia coli was grown with addition of various unsaturated fatty acids. The permeability of the cells for erythritol appeared to be strongly dependent on the fatty acid incorporated in the membrane lipid. Below certain temperatures, depending on the fatty acid incorporated into the lipids, the membrane of the cells became fragile. Mechanical stress on and also rapid cooling of the cells caused release of intracellular cations and small non-electrolyte molecules. By comparison of the cells with liposomes, prepared from synthetic lecithin, the fragility of the cells could be explained as being the consequence of the solidification of the paraffin core Abbreviations: FCCP, p-trifluoromethoxycarbonylcyanide phenylhydrazon

Changes in permeability of Staphylococcus aureus and derived liposomes with varying lipid composition

The physical and barrier properties of the phospholipids phosphatidylglycerol and lysylphosphatidylglycerol were studied in membrane model systems. Packing in monolayers at the air-water interface showed a larger area per molecule for lysylphosphatidylglycerol than for phosphatidylglycerol. The non-electrolyte permeability of liposomes prepared with lysylphosphatidylglycerol was higher than of those prepared with phosphatidylglycerol. On the other hand, the permeability of 86Rb+ was higher for liposomes of phosphatidylglycerol than for those of lysylphosphatidylglycerol. Valinomycin was able to increase the permeability of this cation in the phosphatidylglycerol liposome only. Studies on the effect of the environmental pH on the lysylphosphatidylglycerol to phosphatidylglycerol ratio in intact cells of Staphylococcus aureus showed that the total amount of lysylphosphatidylglycerol, cardiolipin and neutral lipids in the membrane did not change when the pH of the medium was varied between pH 6.5 and 5.0; but the total amount of phosphatidylglycerol decreased when the pH of the medium was lowered. The permeability of the intact cells for erythritol appeared to increase with increasing lysylphosphatidylglycerol to phosphatidylglycerol ratio; whereas the valinomycin mediated exchange of 86Rb+ over the cell membrane appeared to decrease when this ratio was increased. From the correlation between the permeability properties of cells and liposomes the conclusion is drawn that in S. aureus the chemical nature of the phospholipids determines to a great extent the properties of the permeability barrier

Changes in permeability of Staphylococcus aureus and derived liposomes with varying lipid composition

The physical and barrier properties of the phospholipids phosphatidylglycerol and lysylphosphatidylglycerol were studied in membrane model systems. Packing in monolayers at the air-water interface showed a larger area per molecule for lysylphosphatidylglycerol than for phosphatidylglycerol. The non-electrolyte permeability of liposomes prepared with lysylphosphatidylglycerol was higher than of those prepared with phosphatidylglycerol. On the other hand, the permeability of 86Rb+ was higher for liposomes of phosphatidylglycerol than for those of lysylphosphatidylglycerol. Valinomycin was able to increase the permeability of this cation in the phosphatidylglycerol liposome only. Studies on the effect of the environmental pH on the lysylphosphatidylglycerol to phosphatidylglycerol ratio in intact cells of Staphylococcus aureus showed that the total amount of lysylphosphatidylglycerol, cardiolipin and neutral lipids in the membrane did not change when the pH of the medium was varied between pH 6.5 and 5.0; but the total amount of phosphatidylglycerol decreased when the pH of the medium was lowered. The permeability of the intact cells for erythritol appeared to increase with increasing lysylphosphatidylglycerol to phosphatidylglycerol ratio; whereas the valinomycin mediated exchange of 86Rb+ over the cell membrane appeared to decrease when this ratio was increased. From the correlation between the permeability properties of cells and liposomes the conclusion is drawn that in S. aureus the chemical nature of the phospholipids determines to a great extent the properties of the permeability barrier