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This work presents a comparative study of proton transfer activity (PTA) of two cationic (+6) antimicrobial peptides, β-structural arenicin-2 and α-helical melittin. A new approach was proposed for the detection of passive proton transfer by using proteoliposomes containing bacteriorhodopsin, which creates a small light-induced electrochemical proton gradient ∆ΔpH. Addition of several nanomoles of the peptides lowers ∆ΔpH that is proximately indicative of the pore formation. The quantitative analysis of sigmoidal dependences of ∆pH on the peptides concentration was carried out using liposomes prepared from PC, PC/PE, PC/PE/PI and PC/PG. Substitution of PC-containing liposomes with PE-containing ones, having negative spontaneous curvature, reduced the PTA of α-helical melittin and increased that of β-structural arenicin-2. This result indicates an essential difference in the pore formation by these peptides. Further increase of PTA in response to arenicin-2 (in contrast to melittin) was observed in the liposomes prepared from PC/PE/PI. The data analysis leads to the conclusion that PTA is influenced by (i) efficiency of the pore assemblage, which depends on the structure of pore-forming peptides, and the spontaneous curvature of lipids and (ii) the presence of mobile protons in the polar head groups of phospholipids. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Incubation of Micrococcus lysodeikticus protoplasts with phosphatidylcholine liposomes and rat liver exchange proteins (pH 5.1 supernatant fraction) resulted in replacement of about one half of the bacterial total phospholipids by phosphatidylcholine. Protoplasts modified by phosphatidylcholine showed a decreased rate of oxidation of exogenous substrates (NADH, malate) and decreased ferricyanide reductase activity as compared to the initial protoplasts. At the same time incorporation of phosphatidylcholine had no influence on the level of endogenous respiration. Protoplasts modified by phosphatidylcholine were osmotically more stable than the initial protoplasts. After osmotic lysis of the phosphatidylcholine protoplasts their NADH (malate) oxidase and ferricyanide reductase activities were restored. Incorporation of phosphatidylcholine into membrane ghosts, obtained by osmotic rupture of the initial protoplasts had only small if any effect on the malate and NADH oxidase and dehydrogenase activities. It is concluded that phosphatidylcholine is incorporated predominantly into the outer part of cytoplasmic membrane and that protein-mediated transfer of phosphatidylcholine results in restoration of the permeability barrier due to repair of local defects in the initial protoplast membrane. [ABSTRACT FROM AUTHOR]

Affinity resins containing covalently bound phospholipids were used to compare the affinity of the phosphatidylcholine transfer protein from beef liver and a low-specificity-lipid transfer protein from rat hepatoma 27 to phosphatidylcholine and sphingomyelin. Binding experiments demonstrated that the beef liver protein associates specifically with immobilized phosphatidylcholine whereas the hepatoma protein showed a preference for sphingomyelin. Purified antiserum raised against the hepalonia sphingomyelin transfer protein was used to determine the presence of that protein in the cytosol of various experimental tumors as well as in those of normal, regenerating and fetal rat liver. The protein was found to be well expressed in all the tumors examined and in fetal liver as determined by immunodiffusion whereas only minute amounts could be detected in normal liver and in 30-h regenerated liver. The presence of the sphingomyelin transfer protein in cytosol was in parallel with the presence of sphingomyelin in the corresponding mitochondria. It is suggested that the occurrence of sphingomyelin in tumor and fetal liver mitochondria may be due to protein-catalyzed sphingomyelin transfer from the endoplasmic reticulum. [ABSTRACT FROM AUTHOR]

Despite the promising application of liposomes in wool dyeing, little is known about the mechanism of liposome interactions with the wool fiber and dyestuffs. The kinetics of wool dyeing by two dyes, Acid Green 27 (hydrophobic) and Acid Green 25 (hydrophilic), were compared in three experimental protocols: (1) without liposomes, (2) in the presence of phosphatidylcholine (PC) liposomes, and (3) with wool previously treated with PC liposomes. Physicochemical interactions of liposomes with wool fibers were studied under experimental dyeing conditions with particular interest in the liposome affinity to the fiber surface and changes in the lipid composition of the wool fibers. The results obtained indicate that the presence of liposomes favors the retention of these two dyes in the dyeing bath, this effect being more pronounced in case of the hydrophobic dye. Furthermore, the liposome treatment is accompanied by substantial absorption of PC by wool fibers with simultaneous partial solubilization of their polar lipids (more evident at higher temperatures). This may result in structural modification of the cell membrane complex of wool fibers, which could account for a high level of the dye exhaustion observed at the end of the liposome dyeing process.