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1.
Lengthening the spacer of N-acetyl glucosaminyl oligoethoxy cholesterol neoglycolipids from one to seven ethoxy units modified neither the neoglycolipid incorporation into liposomes nor the liposome sizes. Moreover, lengthening the spacer from three to seven units increased the 5(6)-carboxyfluorescein leakage from mixed liposomes. These neoglycolipid-induced disturbances in membrane permeability were corroborated by determining their haemolytic activities. © Rapid Science Ltd. 1998  相似文献   

2.
DD K is an antimicrobial peptide previously isolated from the skin of the amphibian Phyllomedusa distincta. The effect of cholesterol on synthetic DD K binding to egg lecithin liposomes was investigated by intrinsic fluorescence of tryptophan residue, measurements of kinetics of 5(6)-carboxyfluorescein (CF) leakage, dynamic light scattering and isothermal titration microcalorimetry. An 8 nm blue shift of tryptophan maximum emission fluorescence was observed when DD K was in the presence of lecithin liposomes compared to the value observed for liposomes containing 43 mol% cholesterol. The rate and the extent of CF release were also significantly reduced by the presence of cholesterol. Dynamic light scattering showed that lecithin liposome size increase from 115 to 140 nm when titrated with DD K but addition of cholesterol reduces the liposome size increments. Isothermal titration microcalorimetry studies showed that DD K binding both to liposomes containing cholesterol as to liposomes devoid of it is more entropically than enthalpically favored. Nevertheless, the peptide concentration necessary to furnish an adjustable titration curve is much higher for liposomes containing cholesterol at 43 mol% (2 mmol L(-1)) than in its absence (93 micromol L(-1)). Apparent binding constant values were 2160 and 10,000 L mol(-1), respectively. The whole data indicate that DD K binding to phosphatidylcholine liposomes is significantly affected by cholesterol, which contributes to explain the low hemolytic activity of the peptide.  相似文献   

3.
Short oligomers of arginine (R8) have been shown to cross readily a variety of biological barriers. A hypothesis was put forward that inverted micelles form in biological membranes in the presence of arginine oligomer peptides, facilitating their transfer through the membranes. In order to define the role of peptide-lipid interaction in this mechanism, we prepared liposomes as the model membrane to study the ability of R8 inducing calcein release from liposomes, the fusion of liposomes, R8 binding to liposomes and membrane disturbing activity of the bound R8. The results show that R8 binding to liposome membrane depends on lipid compositions, negative surface charge density and interior water phase pH values of liposomes. R8 has no activity to induce the leakage of calcein from liposomes or improve liposome fusion. R8 does not permeabilize through the membrane spontaneously. These peptides delivering drugs through membranes may depend on receptors and energy.  相似文献   

4.
Sendai virus induced leakage of liposomes containing gangliosides   总被引:2,自引:0,他引:2  
Y S Tsao  L Huang 《Biochemistry》1985,24(5):1092-1098
Sendai virus induced liposome leakage has been studied by using liposomes containing a self-quenching fluorescent dye, calcein. The liposomes used in this study were prepared by a freeze and thaw method and were composed of phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine (1:2.60:1.48 molar ratio) as well as various amounts of gangliosides and cholesterol. The leakage rate was calculated from the fluorescence increment as the entrapped calcein leaked out of the liposomal compartment and was diluted into the media. It was shown that the target liposome leakage was virus dose dependent. Trypsin-treated Sendai virus in which the F protein had been quantitatively removed did not induce liposome leakage, indicating that the leakage was a direct result of F-protein interaction with the target bilayer membrane. The activation energy of this process was approximately 12 kcal/mol below 17 degrees C and approximately 25 kcal/mol above 17 degrees C. Gangliosides GM1, GD1a, and GT1b could serve as viral receptor under appropriate conditions. Liposome leakage showed a bell-shaped curve dependence on the concentration of ganglioside in the liposomes. No leakage was observed if the ganglioside content was too low or too high. Inclusion of cholesterol in the liposome bilayer suppressed the leakage rate of liposomes containing GD1a. It is speculated that the liposome leakage is a consequence of fusion between Sendai virus and liposomes.  相似文献   

5.
Targeted liposomal drug formulations may enter cells by receptor-mediated endocytosis and then traffick by membrane flow into acidic intracellular compartments. In order to understand the impact of these intracellular pH changes on liposomal drug unloading, the effect of pH on the release from folate-targeted liposomes of three model compounds with distinct pH dependencies was examined. 5(6)-carboxyfluorescein, which titrates from its anionic to uncharged form following internalization by KB cells, displays strong endocytosis-dependent release, since only its uncharged (endosomal) form is membrane permeable. Endocytosis-triggered unloading of drugs of this sort is enhanced by encapsulating the drug in a weak buffer at neutral pH, so that acidification of the intraliposomal compartment following cellular uptake can occur rapidly. Sulforhodamine B, in contrast, retains both anionic and cationic charges at endosomal pH (~pH 5), and consequently, escapes the endosomes only very slowly. Doxorubicin, which is commonly loaded into liposomes in its membrane-impermeable (cationic) form using an acidic buffer, still displays endocytosis-triggered unloading, since sufficient uncharged doxorubicin remains at endosomal pHs to allow rapid re-equilibration of the drug according to the new proton gradient across the membrane. In this case, when the extraliposomal [H+] increases 250-fold from 4 × 10–8 M (pH 7.4, outside the cell) to 10–5 M (pH 5, inside the endosome), the ratio of doxorubicin inside to outside the liposome must decrease by a factor of 250. Therefore, the collapse of the transliposomal pH gradient indirectly drives an efflux of the drug molecule from the liposome. Since a change in intraliposomal pH is not required to unload drugs of this type, the intraliposomal compartment can be buffered strongly at acidic pH to prevent premature release of the drug outside the cell. In summary, pH triggered release of liposome-encapsulated drugs can be achieved both with drugs that increase as well as decrease their membrane permeabilities upon acidification, as long as the intraliposomal buffer strength and pH is rationally selected.  相似文献   

6.
H Ellens  J Bentz  F C Szoka 《Biochemistry》1986,25(2):285-294
We have examined whether there is a relationship between the lamellar-hexagonal phase transition temperature, TH, and the initial kinetics of H+- and Ca2+-induced destabilization of phosphatidylethanolamine (PE) liposomes. The liposomes were composed of dioleoylphosphatidylethanolamine, egg phosphatidylethanolamine (EPE), or phosphatidylethanolamine prepared from egg phosphatidylcholine by transesterification (TPE). These lipids have well-spaced lamellar-hexagonal phase transition temperatures (approximately 12, approximately 45, and approximately 57 degrees C) in a temperature range that allows us to measure the initial kinetics of bilayer destabilization, both below and above TH. The liposomes were prepared at pH 9.5. The TH of EPE and TPE was measured by using differential scanning calorimetry, and it was found that the TH was essentially the same at low pH or at high pH in the presence of 20 mM Ca2+. At temperatures well below TH, either at pH 4.5 or at pH 9.5 in the presence of Ca2+, the liposomes aggregate, leak, and undergo lipid mixing and mixing of contents. We show that liposome/liposome contact is involved in the destabilization of the PE liposomes. The temperature dependence of leakage, lipid mixing, and mixing of contents shows that there is a massive enhancement in the rate of leakage when the temperature approaches the TH of the particular PE and that lipid mixing appears to be enhanced. However, the fusion (mixing of aqueous contents) is diminished or even abolished at temperatures above TH. At and above the TH, a new mechanism of liposome destabilization arises, evidently dependent upon the ability of the PE molecules to adapt new morphological structures at these temperatures. We propose that this destabilization demarks the first step in the pathway to the eventual formation of the HII phase. Thus, the polymorphism accessible to PE is a powerful agent for membrane destabilization, but additional factors are required for fusion.  相似文献   

7.
The aggregation of biotinylated phospholipid vesicles (liposomes) cross-linked by antibiotin IgG was studied experimentally and theoretically. The liposomes were either low density liposomes that contained 0.4 mol% biotinylated phospholipid ( approximately 100 exposed biotin molecules per liposome), or high density liposomes that contained 2.7 mol% biotinylated phospholipid ( approximately 1000 exposed biotin molecules per liposome). The solution turbidity and mean particle size measured by quasi-elastic light scattering (QLS) were monitored throughout the aggregation. Three different lots of antibiotin antibodies, each with different association constants and binding heterogeneities, were used. The antibody binding characteristics affected the aggregation rates. The aggregation kinetics were analyzed using a model based on the Smoluchowski theory of aggregation, fractal concepts of aggregate microstructure, and Rayleigh and Mie light scattering theory. The experimental conditions of liposome concentration, protein concentration, and ligand density under which aggregation occurred correlated well with calculated sticking probabilities based on isotherms describing the adsorption of antibiotin antibody to the liposomes. These results are compared with prior observations made when avidin was used as the cross-linking protein. (c) 1996 John Wiley & Sons, Inc.  相似文献   

8.
The effects of human recombinant tumor necrosis factor (TNF) and interferon-gamma (IFN-gamma) in damage of liposome membranes were examined to elucidate the molecular mechanism of their antiproliferative actions on tumor cells. The extent of membrane damage was assayed by measuring the rate of release of the fluorescent dye calcein encapsulated in the liposomes at different pH values in the presence of TNF and/or IFN-gamma. At pH values below about 5, TNF bound to phospholipid liposomes composed of mixtures of phosphatidyl-serine and phosphatidylcholine in molar ratios of 2:1 and 1:2 and caused rapid release of calcein. In contrast, IFN-gamma induced very slow leakage of dye although it bound almost completely to the membranes, suggesting that it causes much less membrane damage than TNF. Small amounts of these two antitumor factors bound to phosphatidylcholine liposomes in the pH range of 4-7, inducing relatively slow leakage of calcein. In the presence of both TNF and IFN-gamma at pH 5, the maximal leakage rate was twice the sum of the rates with the two proteins individually, and the rate depended on the TNF/IFN-gamma ratio, indicating synergistic effects of TNF and IFN-gamma in induction of membrane damage. These different and synergistic actions on liposome membranes may account for the different antitumor properties of the two antitumor cytokines and their synergism.  相似文献   

9.
A novel type of liposome bilayer destabilization catalyzed by the enzyme, beta-galactosidase, is described. Unsaturated phosphatidylethanolamine (PE), an HII-phase-forming lipid, does not form stable liposomes at physiological temperature and pH. However, stable unilamellar liposomes can be prepared by mixing PE with a minimum of 5 mol% ganglioside GM1, a micellar-phase-forming lipid. Treatment of these GM1/PE liposomes with beta-galactosidase induces a rapid leakage (3-6 min) of the entrapped fluorescent dye, calcein. The studies indicate that liposome destabilization is the result of catalytic degradation of GM1, rather than a stoichiometric binding of GM1 by beta-galactosidase. Kinetic data indicate that the destabilization takes place via liposome collision. This simple, rapid method of liposome destabilization by beta-galactosidase will be useful in designing a liposome-based signal amplification mechanism for assays involving enzymes.  相似文献   

10.
The interaction of liposomes with macrophage cells was monitored by a new fluorescence method (Hong, K., Straubinger, R.M. and Papahadjopoulos, D., J. Cell Biol. 103 (1986) 56a) that allows for the simultaneous monitoring of binding, endocytosis, acidification and leakage. Profound differences in uptake, cell surface-induced leakage and leakage subsequent to endocytosis were measured in liposomes of varying composition. Pyranine (1-hydroxypyrene-3,6,8-trisulfonic acid, HPTS), a highly fluorescent, water-soluble, pH sensitive dye, was encapsulated at high concentration into the lumen of large unilamellar vesicles. HPTS exhibits two major fluorescence excitation maxima (403 and 450 nm) which have a complementary pH dependence in the range 5-9: the peak at 403 nm is maximal at low pH values while the peak at 450 nm is maximal at high pH values. The intra- and extracellular distribution of liposomes and their approximate pH was observed by fluorescence microscopy using appropriate excitation and barrier filters. The uptake of liposomal contents by cells and their subsequent exposure to acidified endosomes or secondary lysosomes was monitored by spectrofluorometry via alterations in the fluorescence excitation maxima. The concentration of dye associated with cells was determined by measuring fluorescence at a pH independent point (413 nm). The average pH of cell-associated dye was determined by normalizing peak fluorescence intensities (403 nm and 450 nm) to fluorescence at 413 nm and comparing these ratios to a standard curve. HPTS-containing liposomes bound to and were acidified by a cultured murine macrophage cell line (J774) with a t1/2 of 15-20 min. The acidification of liposomes exhibited biphasic kinetics and 50-80% of the liposomes reached an average pH lower than 6 within 2 h. A liposomal lipid marker exhibited a rate of uptake similar to HPTS, however the lipid component selectively accumulated in the cell; after an initial rapid release of liposome contents, 2.5-fold more lipid marker than liposomal contents remained associated with the cells after 5 h. Coating haptenated liposomes with antibody protected liposomes from the initial release. The leakage of liposomal contents was monitored by co-encapsulating HPTS and p-xylene-bis-pyridinium bromide, a fluorescence quencher, into liposomes. The time course of dilution of liposome contents, detected as an increase in HPTS fluorescence, was coincident with the acidification of HPTS. The rate and extent of uptake of neutral and negatively charged liposomes was similar; however, liposomes opsonized with antibody were incorporated at a higher rate (2.9-fold) and to a greater extent (3.4-fold).(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

11.
Rhodanese (thiosulfate cyanide sulfurtransferase; E.C. 2.8.1.1) is a mitochondrial enzyme that is unprocessed after import. We describein vitro experiments showing that partially folded rhodanese can interact with lipid bilayers. The interaction was monitored by measuring the ability of rhodanese to disrupt small unilamellar vesicles composed of phosphatidylserine and to release 6-carboxyfluorescein that was trapped in the liposomes. Partially folded rhodanese, derived by dilution of urea-unfolded enzyme, efficiently induced liposome leakage. Native rhodanese had no effect on liposome integrity. Liposome disruption progressively decreased as rhodanese was given the opportunity to refold or aggregate before introduction of the liposomes. A synthetic 23 amino acid peptide representing the N-terminal sequence of rhodanese was very efficient at disrupting the liposomes. Shorter peptides chosen from within this sequence (residues 11–23 or residues 1–17) had no effect on liposome disruption. A peptide representing the tether region that connects the domains of the enzyme was also without effect. These results are consistent with the hypothesis that the N-terminal sequence of rhodanese is an uncleaved leader sequence, and can interact with membrane components that are involved in the mitochondrial uptake of this protein.  相似文献   

12.
Kurganov B  Doh M  Arispe N 《Peptides》2004,25(2):217-232
To compare both the peptide molecular self-aggregation and the interaction with membrane lipids of the Alzheimer's amyloid beta (Abeta)40, Abeta42 peptides, and the cytotoxic peptides human amylin and prion (106-126) peptides, we applied a liposome aggregation technology. The kinetics of the changes in the optical density (DeltaOD) of liposome suspensions generated by the aggregation of liposomes induced by these peptides, allowed us to comparatively analyze their phospholipid affinity and self-aggregation. The kinetic curves showed an initial nonlinear region where d(DeltaOD)/dt followed first order kinetics corresponding to the binding of the peptides to the membrane of the liposome, a linear region where d(DeltaOD)/dt was constant, corresponding to the interaction between two membrane-bound peptide molecules, and a final slower increasing nonlinear region that corresponds to nucleation or seeding of aggregation. The analysis of the aggregation curves demonstrated that amylin and prion peptides also showed affinity for the acidic phospholipid phosphatidylserine (PS), as it has previously been shown for the Alzheimer's Abeta40, Abeta42 peptides. Abeta42 showed the highest, and amylin the lowest, affinity for the liposome membrane. When bound to the membrane of the liposomes, all the peptides preserved the self-aggregation characteristics observed in solution. Aging the Abeta40 and Abeta42 peptide solutions that permit molecular self-aggregation reduced their capacity to induce liposome aggregation. The self-aggregation of membrane-bound prion molecules was several orders of magnitude higher than that observed for the other toxic peptides. Incorporation of the ganglioside GM1 into the membrane of liposomes enhanced the peptide-induced liposome aggregation. Kinetic analysis revealed that this enhancement was due to facilitation of the formation of bridges between membrane-bound peptide molecules, demonstrating that the peptide-membrane interaction and the peptide amyloidogenesis are independent functions performed at separate molecular regions.  相似文献   

13.
Unilamellar liposomes composed of phosphatidylcholine with an entrapped self-quenching fluorescent dye, calcein, were immobilized in chromatographic gel beads by avidin-biotin binding. Bee venom phospholipase A(2) (PLA(2)) was applied in a small amount onto the immobilized liposome column. The release of calcein from the immobilized liposomes resulting from the catalyzed hydrolysis of the phospholipids was detected online by immobilized liposome chromatography (ILC) using a flow fluorescent detector. The PLA(2)-catalyzed membrane leakage of the immobilized liposomes as studied with ILC was found to be affected by the gel pore size used for immobilization, by liposome size, and as expected by the concentration of calcium, but was unaffected by the flow rate of ILC. The largest PLA(2)-induced calcein release from the liposome column was detected on large unilamellar liposomes immobilized on TSK G6000PW or Sephacryl S-1000 gel in the presence of 1 mM Ca(2+) in the aqueous mobile phase. Comparison with the PLA(2)-catalyzed membrane leakage in free liposome suspensions, we conclude that the fluorescent leakage from liposomes hydrolyzed by PLA(2) can be rapidly and sensitively detected by ILC runs using large amount of immobilized liposomes with entrapped fluorescent dye.  相似文献   

14.
The circular dichroism (CD) active phospholipid bis(4'-n-octanoxyazobenzene-4-carboxyl)-L-alpha-phosphatidylcholin e (CDPC) was used to study the effects of carboxymethyl-chitin (CM-chitin) on the membrane dynamics. For this purpose, CD and electronic spectra were observed for a mixture of CM-chitin and liposomes composed of CDPC and egg lecithin (EPC) (50% CDPC-EPC-liposomes), and for a mixture of CM-chitin, 50% CDPC-EPC-liposomes, and EPC-liposomes. CM-chitin at concentrations higher than ca. 10(-5) M induced the increase of absorbance at 600 nm synchronized with the dilution of CDPC in 50% CDPC-EPC-liposomes by EPC matrix, indicating that CM-chitin induces the fusion among a few liposomes and/or the lipid transfer through the transient liposome fusion. Temperature dependent CD spectra of a mixture of the 50% CDCP-EPC-liposomes and CM-chitin suggested that even high concentration of CM-chitin has no significant perturbation of the lipid organization in the membranes. The effects of CM-chitin on the leakage of [3H]sucrose from the EPC-liposomes were also studied. By the presence of 5 X 10(-6) M CM-chitin, the half-life for leakage of [3H]sucrose in plasma was increased by 4 times. This effect of CM-chitin was reduced by chitinase, while no effect was observed with lysozyme, suggesting that CM-chitin molecules are adsorbed on the liposome surface and stabilize the liposomes against the plasma proteins.  相似文献   

15.
The bifunctional Bordetella adenylate cyclase toxin-hemolysin (ACT) penetrates target cell membranes, forms cation-selective channels and subverts cellular signaling by catalyzing uncontrolled conversion of ATP to cAMP. While primarily targeting phagocytes expressing the alphaMbeta2 integrin (CD11b/CD18), the toxin can also penetrate mammalian erythrocytes lacking the receptor and membrane endocytosis. We sought here to analyze the membrane interactions of ACT in a liposome model. Insertion of ACT into liposome membranes required calcium and caused leakage of entrapped fluorescent probes due to liposome disruption, as indicated by similar release kinetics for the approximately 398 Da FITC probe and its approximately 4400 Da dextran conjugate. However, the non-acylated proACT, which does not penetrate cellular membranes, exhibited higher capacity to bind and lyze liposomes than the mature toxin, showing that the fatty-acyl modification was not required for penetration of ACT into the lipid bilayer. Individual deletions within the channel-forming, acylation and repeat domains of ACT abolished its capacity to disrupt both liposomes and erythrocytes. In contrast to erythrocyte binding, however, the liposome binding was only lost upon a simultaneous deletion of both the channel-forming and acylation domains, suggesting that the acylation domain was also involved in liposome penetration of ACT. Moreover, substitutions of glutamates 509 and 516 by lysines, which strongly enhanced the channel-forming and hemolytic activity of ACT, did not affect its capacity to disrupt liposomes. This shows that the mechanism of ACT action in cellular membranes is not fully reproduced in liposome membranes.  相似文献   

16.
The effect of 2.45 GHz microwave radiation on the permeability of unilamellar phosphatidylcholine liposomes has been studied. Leakage of 5(6)-carboxyfluorescein from the liposomes was measured using spectrofluorimetry after exposure to either microwaves or thermal heating for 5–20 min intervals. The exposure temperature, 37.6 ± 0.5°C, was well above the phase transition temperature of the lipid membrane. The microwave exposure did not result in any non-thermal increase in permeability above that produced by thermal heating. This study refutes the results reported by Saalman et al. [1] in which an increased liposome permeability due to microwave exposure was reported. The refined analysis in the present study shows that this increased liposome permeability was not a non-thermal microwave effect.  相似文献   

17.
H Ellens  J Bentz  D Mason  F Zhang  J M White 《Biochemistry》1990,29(41):9697-9707
Influenza virus gains access to the cytoplasm of its host cell by means of a fusion event between viral and host cell membrane. Fusion is mediated by the envelope glycoprotein hemagglutinin (HA) and is triggered by low pH. To learn how many hemagglutinin trimers are necessary to cause membrane fusion, we have used two NIH 3T3 fibroblast cell lines that express HA protein at different surface densities. On the basis of quantitations of the number of HA trimers per cell and the relative surface areas of the two cell lines, the HAb-2 cells have a 1.9-fold higher plasma membrane surface density than the GP4F cells. The membrane lateral diffusion coefficient and the mobile fraction for HA is the same for both cell lines. A Scatchard analysis of the binding of glycophorin-bearing liposomes to the cells showed 1700 binding sites for the GP4F cells and 3750 binding sites for the HAb-2 cells, with effectively the same liposome-cell binding constant, about 7 x 10(10) M-1. Binding was specific for glycophorin on the liposomes and HA expressed on the cells. A competition experiment employing toxin-containing and empty liposomes allowed us to quantitate the number of liposomes that fused per cell, which was a small constant fraction of the number of bound liposomes. For the HAb-2 cells, about 1 in every 70 bound liposomes fused and for the GP4F cells about 1 in every 300 bound liposomes fused. Hence, the HAb-2 cells showed 4.4 times more fusion per bound liposome, even though the surface density of HA was only 1.9 times greater. We conclude the following: (i) One HA trimer is not sufficient to induce fusion. (ii) The HA bound to glycophorin is not the HA that induces fusion. That is, even though each HA has a binding and a fusion function, those functions are not performed by the same HA trimer.  相似文献   

18.
Nisin Z, a natural nisin variant, was recently isolated from Lactococcus lactis subspecies lactis NIZO 22186. The gene for this lantibiotic, designated nisZ, has been cloned, and its nucleotide sequence was found to be identical to that of the precursor nisin gene with the exception of a single mutation resulting in the substitution of Asn-27 for His-27 in the mature polypeptide (J. W. M. Mulders, I. J. Boerrigter, H. S. Rollema, R. J. Siezen, and W. M. de Vos, Eur. J. Biochem. 201:581-584, 1991). A K+ electrode was used to investigate the effect of various environmental parameters on the action of nisin Z against Listeria monocytogenes. Addition of nisin Z resulted in immediate loss of cell K+, depolarization of the cytoplasmic membrane, inhibition of respiratory activity, and hydrolysis and partial efflux of cellular ATP. The action of nisin Z was optimal at pH 6.0 and was significantly reduced by di- and trivalent cations. The lanthanide gadolinium (Gd3+) was an efficient inhibitor and prevented nisin Z activity completely at a concentration of 0.2 mM. Nisin Z-induced loss of cell K+ was reduced at low temperatures, presumably as a result of the increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane. In cells grown at 30°C, the action of nisin Z was prevented below 7°C, whereas in cells grown at 4°C nisin Z was able to induce K+ leakage at this low temperature.  相似文献   

19.
Nystatin interaction with liposomes mimicking fungal and mammalian membranes (ergosterol- and cholesterol-containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) large unilamellar vesicles, respectively) was studied by fluorescence spectroscopy. The activity of this antibiotic was also measured using a pyranine fluorescence detected K+/H+ exchange assay. Nystatin mean fluorescence lifetime varied with the antibiotic concentration and ergosterol content (0-30 mol%) of the lipid vesicles. It sharply increased from 5 to 37 ns upon reaching 100 molecules per liposome, reporting nystatin oligomerization in the membrane. Concomitantly, spectral alterations typical of excitonic coupling were detected and there was a pronounced increase in the initial rate of pore formation by nystatin. These findings suggest that nystatin exerts its antibiotic activity via a two-stage mechanism: at low antibiotic concentrations, surface-adsorbed monomeric antibiotic molecules perturb the lipid packing, changing the permeability properties of the ergosterol-rich liposomes. Upon reaching a critical threshold, nystatin mode of action switches to the classical model of transmembrane aqueous channel formation. In the presence of cholesterol-containing POPC liposomes, neither nystatin spectroscopic properties, nor the kinetics of K+ efflux varied with the antibiotic concentration suggesting that in this case the first stage of antibiotic mode of action always prevails or the assemblies formed by nystatin and cholesterol are very loose.  相似文献   

20.
Liposome entrapment may improve activity of protein or polypeptide antimicrobials against a variety of microorganisms. In this study, ability of liposomes to withstand exposure to environmental and chemical stresses typically encountered in foods and food processing operations were tested. Liposomes consisting of distearoylphosphatidylcholine (PC) and distearoylphosphatidylglycerol (PG), with 0, 5, or 10 μg/ml of the antimicrobial peptide nisin entrapped, were exposed to elevated temperatures (25–75 °C) and a range of pH (5.5–11.0). Ability of liposomes to maintain integrity was assessed by measuring the encapsulation efficiency (EE), ζ-potential, and particle size distribution of liposomes. Distearoylphosphatidylcholine, PC/PG 8:2, and PC/PG 6:4 (mole fraction) liposomes retained between ~70–90% EE despite exposure to elevated temperature and alkaline or acidic pH. Particle size of liposomes averaged between 100 and 240 nm depending on liposome preparation. Liposomal surface charge depended primarily on phospholipid composition and changed little with inclusion of nisin. Surface charge was not affected by temperature for PC and PC/PG 8:2 but decreased for PC/PG 6:4 liposomes. Our results suggest that liposomes containing nisin may be suitable for use as antimicrobial-active ingredients in low- or high-pH foods subjected to moderate heat treatments.  相似文献   

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