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At least 19 recordsLinked to original sources
PubMed1985

Spiroplasma membrane lipids.

Membranes of six spiroplasma strains belonging to different Spiroplasma species and subgroups were isolated by a combination of osmotic lysis and sonication in the presence of EDTA to block endogenous phospholipase activity. Analysis of membrane lipids showed that in addition to free and esterified cholesterol the spiroplasmas incorporated exogenous phospholipids from the growth medium. Sphingomyelin was preferentially incorporated from phosphatidylcholine-sphingomyelin vesicles or from the serum used to supplement the growth medium. Palmitate was incorporated better than oleate into membrane lipids synthesized by the organisms during growth. The major phospholipid synthesized by the spiroplasmas was phosphatidylglycerol. The positional distribution of the fatty acids in phosphatidylglycerol of Spiroplasma floricola resembled that found in Mycoplasma species, in which the saturated fatty acids prefer position 2 in the glycerol backbone and not position 1 as found in Acholeplasma species and elsewhere in nature. Electron paramagnetic resonance analysis of spin-labeled fatty acids incorporated into S. floricola membranes exhibited homogeneous single-component spectra without immobilized regions. The S. floricola membranes were more rigid than those of Acholeplasma laidlawii and less rigid than those of Mycoplasma gallisepticum.

Cholesterol↗
PubMed1996

Plasma lipids, erythrocyte membrane lipids and blood pressure of hypertensive women after ingestion of dietary oleic acid from two different sources.

OBJECTIVE: To study the effect of a diet rich in mono-unsaturated fatty acids (MUFA), from high-oleic sunflower oil (HOSO) and olive oil, on plasma lipids, erythrocyte membrane lipids (including fatty acid composition) and blood pressure of hypertensive (normocholesterolaemic or hypercholesterolaemic) women. METHODS: There were 16 participants who were hypertensive women aged 56.2 +/- 5.4 years. The participants ate a diet enriched with HOSO or olive oil for two 4-week periods with a 4-week washout period before starting the second type of MUFA diet. At entry and during study of each diet, plasma lipids and apolipoproteins were measured by conventional enzymatic methods. Erythrocyte membrane lipid and fatty acid compositions were analysed by means of the latroscan thin-layer chromatography/flame ionization detection technique and by gas chromatography, respectively. Blood pressure was also measured. The statistical analysis was conducted by using Student's two-tailed paired t-test. RESULTS: In both groups of hypertensive patients, there was a significant increase in plasma high-density lipoprotein (HDL) cholesterol concentration after the HOSO or olive oil diets, with regard to baseline. Additionally, a significant decrease in plasma HDL2 cholesterol concentration and an increase in plasma HDL3 cholesterol concentration were evident. The membrane free-cholesterol concentration increased significantly and the phospholipid concentration decreased significantly in erythrocytes after the olive oil diet, though both MUFA diets produced a significant decrease in the concentration of membrane esterified cholesterol. Therefore, the molar ratio of cholesterol to phospholipids was raised significantly in the erythrocyte membrane of hypertensive women after the dietary olive oil, but not after the HOSO diet. In the hypertensive and normo-cholesterolaemic group the HOSO diet significantly increased the content in the erythrocyte membrane of oleic, eicosenoic, arachidonic and docosapentaenoic acids, whereas the olive oil diet increased the content of palmitoleic acid and long-chain polyunsaturated fatty acids of the n-3 family besides, compared with baseline. A significant decrease in linoleic acid was also evident. In the hypertensive and hypercholesterolaemic group, the HOSO diet resulted in significant increases in palmitoleic, oleic, eicosenoic and behenic acids, whereas the olive oil diet enhanced the content of arachidonic, docosapentaenoic and docosahexaenoic acids besides, with respect to baseline. In addition, there was a significant decrease in stearic acid, but only after dietary olive oil was there a decrease in linoleic acid. The most important differences between the two MUFA diets were the increase in n-3 fatty acids and the decrease in the n-6; n-3 fatty acids ratio after dietary olive oil in the erythrocyte membranes of hypertensive patients. Interestingly, a significant reduction in systolic and diastolic blood pressures was only evident after the ingestion of olive oil. CONCLUSION: These data suggest that the beneficial effects of dietary olive oil on the plasma lipids and lipoprotein profile, lipid and fatty acid composition of erythrocyte membrane, and blood pressure in women with untreated essential hypertension are not found equally for the HOSO-rich diet, despite both vegetable oils providing a similar concentration of MUFA.

Aged↗
PubMed1985

Role of membrane lipids and membrane fluidity in thermosensitivity and thermotolerance of mammalian cells.

The role of membrane lipids and membrane fluidity in thermosensitivity of mammalian cells is not well understood. The limited experimental data in the literature have led to conflicting results. A detailed investigation of lipid composition and membrane fluidity of cellular membranes was undertaken to determine their relationship to cell survival after hyperthermia. Ehrlich ascites (EA) cells, mouse fibroblast LM cells, and HeLa S3 cells differed in thermosensitivity as expressed by a D0 of 3.1, 5.2, and 9.7 min, respectively, at 44 degrees C. No correlation with cellular thermosensitivity could be found with respect to the amount of cholesterol and to the cholesterol to phospholipid ratio in the particulate fraction of the cells. By growing the cells for some generations in different media, cholesterol and phospholipid content could be changed in the particulate fraction, but no difference in cell survival was observed. When mouse fibroblasts were grown for 24 hr in a serum-free medium supplemented with arachidonic acid (20:4), all subcellular membranes were about eight times richer in phospholipids containing polyunsaturated acyl (PUFA) chains and membrane fluidity was increased as measured by fluorescence polarization of diphenylhexatriene (DPH). The alterations resulted in a higher thermosensitivity. When mouse fibroblasts were made thermotolerant no change in cholesterol and phospholipid content could be found in the particulate fraction of the cells. The relative weights and the quality of the phospholipids as well as the fatty acid composition of the phospholipids appeared to be the same for normal and thermotolerant cells. Fluidity measurements in whole cells, isolated plasma membranes, and liposomes prepared from phospholipids extracted from the cells revealed no significant differences between normal and thermotolerant fibroblasts when assayed by fluorescence polarization (DPH) and electron spin resonance (5-nitroxystearate). It is concluded that the mechanism of thermal adaptation resulting in differences in lipid composition as reported in the literature differs from the mechanism of the acquisition of thermal tolerance. The lower heat sensitivity of thermotolerant cells, as initiated by a nonlethal triggering heat dose followed by an induction period at 37 degrees C, does not involve changes in lipid composition and membrane fluidity. However, a prompt and clear (also nonlethal) change in membrane fluidity by an increase in PUFA does result in an increased thermosensitivity, probably because of an indirect effect via the lipids in causing disfunctioning of proteins in the membrane and/or the cytoskeleton.

Acclimatization↗
PubMed1992

Red blood cell susceptibility to lipid peroxidation, membrane lipid composition, and antioxidant enzymes in continuous ambulatory peritoneal dialysis patients.

OBJECTIVE: To investigate the overall susceptibility of red blood cells (RBC) to lipid peroxidation from patients on continuous ambulatory peritoneal dialysis (CAPD). METHODS: The following parameters were measured: RBC malondialdehyde (MDA) production after oxidative stress with H2O2, RBC antioxidant enzymes glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), and RBC membrane lipid composition. The levels of plasma vitamin E and serum selenium were also assayed. PATIENTS: Eleven patients on continuous ambulatory peritoneal dialysis. Twenty-one healthy blood donors of similar age were used as normal controls. RESULTS: The MDA formation after H2O2 stimulation was normal in CAPD patients (0.79 +/- 0.1 mumol/gHb versus 0.78 +/- 0.1 in the control group). RBC from CAPD patients also showed a normal SOD activity, a more than adequate vitamin E status, and a peculiar pattern of membrane lipids, with reduced polyunsaturated fatty acids (p less than 0.001) and increased monounsaturated fatty acids (p less than 0.001). Both RBC GSH-Px activity, a selenium-dependent enzyme, and serum selenium levels were significantly lower in CAPD patients, and a significant positive correlation (r = 0.68; p less than 0.02) between the two parameters was found. CONCLUSIONS: This study found a normal sensitivity to oxidant stress in RBC from a group of CAPD patients, despite an impaired GSH-Px activity. The peculiar lipid pattern of RBC membrane, characterized by reduced PUFA and increased MUFA content, may contribute, in addition to adequate SOD activity and vitamin E status, to normal RBC lipid peroxidation.

Aged↗
PubMed1984

Interaction of saponin and digitonin with black lipid membranes and lipid monolayers.

The effects of the plant glycosides saponin as well as digitonin on the electrical conductance of black lipid membranes and the effect of these agents on the surface pressure of lipid monofilms was investigated. Both saponin and digitonin induced channel-like fluctuations in planar bilayers made either of diphytanoylphosphatidylcholine ( DPhPC ) or of DPhPC and cholesterol 2: 1 (w/w). In cholesterol-free bilayers the amount needed to induce an increase in conductance was 0.3-1 mg/ml for saponin and about 0.2 mg/ml for digitonin. In contrast, in cholesterol-containing bilayers the concentration needed to induce pores was about 10 micrograms/ml for both saponin and digitonin. In cholesterol-containing membranes the fluctuating pores induced by saponin were about 3-times more permeable to K+ than to Cl- and the macroscopic current showed an ohmic behaviour. Surface pressure experiments demonstrate that both glycosides could penetrate into lipid monofilms of pure DPhPC spread at the air/water interface with an initial surface pressure of 30 mN/m. The increase in surface pressure was considerably enhanced in cholesterol-containing films. It is assumed that the channel-like fluctuations induced by saponin as well as digitonin, in both cholesterol-free and cholesterol-rich bilayers are due to the formation of micellar structures within the lipid lattice. Probably the penetration of the glycosides into the lipid bilayer is considerably enhanced by the presence of cholesterol.

Animals↗
PubMed1981

Total lipid and membrane lipid analysis of normal animal and human lenses.

Comparisons of lens fiber cell membrane isolation methods were made. Although membrane lipid yield from stirring overnight in hypotonic medium followed by low-speed centrifugation was comparable to that from homogenization and high-speed centrifugation, losses in phosphatidyl ethanolamine were observed with the former method. Lyophilization with vacuum replacement by nitrogen did not exert any deleterious effects. A significant difference in total lens lipid was observed between human and the three species of animals investigated.

Aged↗
PubMed1992

Black lipid membranes of tetraether lipids from Thermoplasma acidophilum.

Black lipid membranes were formed of tetraether lipids from Thermoplasma acidophilum and compared to the bilayer forming lipids diphytanoylphosphatidylcholine and diphythanylglucosylglycerol. Bilayer-forming lipids varied in thickness of black lipid membranes due to the organic solvent used. Measurements of the specific membrane capacitance (Cm = 0.744 microF/cm2) showed that the membrane-spanning tetraether lipids from Thermoplasma acidophilum form a monolayer of a constant thickness of 2.5-3.0 nm no matter from which solvent. This finding corresponds to the results of Gliozzi et al. for the lipids of another archaebacterium, Sulfolobus solfataricus. Black lipid membranes were formed at room temperature with a torus from bilayer-forming lipids, however, the torus could also be formed by the tetraether-lipid itself at room temperature and at defined concentration. In these stable black lipid membranes, conductance was measured in the presence of valinomycin, nonactin, and gramicidin. At 10(-7) M concentration, valinomycin mediated higher conductance in membranes from tetraether lipids (200-1200 microS/cm2) than from bilayer-forming lipids (125-480 microS/cm2). Nonactin, at 10(-6) M concentration, mediated a 6-fold higher conductance in a tetraether lipid membrane than in a bilayer, whereas conductance, in the presence of 5 x 10(-11) M gramicidin could reach higher values in bilayers than in tetraether lipid monolayers of comparable thickness. Monensin did not increase the conductance of black lipid membranes from tetraether lipids under all conditions applied in our experiments. Poly(L-lysine) destroyed black lipid membranes. Lipopolysaccharides from Thermoplasma acidophilum were not able to form stable black lipid membranes by themselves. The lipopolysaccharide complexes from Thermoplasma acidophilum and from Escherichia coli decreased the valinomycin-mediated conductance of monolayer and bilayer membranes. This influence was stronger than that of the polysaccharide dextran.

Electric Conductivity↗
PubMed1999

Stress tolerance in a yeast lipid mutant: membrane lipids influence tolerance to heat and ethanol independently of heat shock proteins and trehalose.

The response of a yeast unsaturated fatty acid auxotroph, defective in delta 9-desaturase activity, to heat and ethanol stresses was examined. The most heat- and ethanol-tolerant cells had membranes enriched with oleic acid (C18:1), followed in order by cells enriched with linoleic (C18:2) and linolenic (C18:3) acids. Cells subjected to a heat shock (25-37 degrees C for 30 min) accumulated trehalose and synthesized typical heat shock proteins. Although there were no obvious differences in protein profiles attributable to lipid supplementation of the mutant, relative protein synthesis as determined by densitometric analysis of autoradiograms suggested that hsp expression was different. However, there was no consistent relationship between the synthesis of heat shock proteins and the acquisition of thermotolerance in the lipid supplemented auxotroph or related wild type. Furthermore, trehalose accumulation was also not closely related to stress tolerance. On the other hand, the data presented indicated a more consistent role for membrane lipid composition in stress tolerance than trehalose, heat shock proteins, or ergosterol. We suggest that the sensitivity of C18:3-enriched cells to heat and ethanol may be attributable to membrane damage associated with increases in membrane fluidity and oxygen-derived free radical attack of membrane lipids.

Electrophoresis, Polyacrylamide Gel↗
PubMedDate not supplied

Does membrane lipid profile explain chilling sensitivity and membrane lipid phase transition of spermatozoa and oocytes?

Ram, fowl and bee spermatozoa, and oocytes of cows and zebrafish were used to study lipid membrane profiles, chilling sensitivity and lipid-phase transitions. The integrity of the membranes was determined by carboxyfluorescein diacetate (CFDA) staining following exposure for 15 minutes to low temperatures. Ram and fowl spermatozoa showed different degrees of loss of membrane integrity. Surprisingly, bee spermatozoa did not show any sensitivity to chilling, and their membranes remained intact down to 0 degree C. In bovine oocytes (at the GV stage) chilling injury was very severe at 16 degree C (membrane integrity decreased by 50%). Lipid phase transition (LPT) and membrane fluidity, which were evaluated by Fourier transform infrared (FTIR) microscopy, and fluorescence polarisation, showed phase transitions at the same temperatures as caused damage (between 30 and 12 degree C). The membrane lipid profiles showed high concentrations of polyunsaturated fatty acids (PUFA) in cold-sensitive ram spermatozoa and zebrafish oocytes, but the ratio between PUFA and saturated fatty acids was highest in cold-resistant bee spermatozoa and lowest in cold-sensitive bovine oocytes. These results suggest a close relationship among cold susceptibility, lipid phase transition and lipids profile in animal gametes.

Journal Article↗
PubMed1995

Effects of peroxisomal beta-oxidation antagonist on 2',3'-cyclic-nucleotide 3'-phosphohydrolase, membrane lipid compositions, and membrane fluidity in C-6 glial cells.

In order to understand the relationship between peroxisomal dysfunction and clinical manifestations of peroxisomal disorders, the effect of thioridazine, a peroxisomal beta-oxidation antagonist, on the differentiation, membrane lipid composition and membrane fluidity of C-6 glial cells was examined. In our study, induction of 2',3'-cyclic-nucleotide 3'-phosphohydrolase (CNP), which was considered to be a membrane-associated enzyme closely associated with myelination, was inhibited with supplementation of thioridazine, followed by an increase in the relative concentration of longer chain fatty acids in cell membrane lipids, indicating that thioridazine causes impaired differentiation in the glial stem cell system. Membrane fluidity of C-6 glial cells was examined using a fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The DPH anisotropy value was decreased in the glial cells treated with thioridazine. These results indicate that the alteration of the membrane lipid composition caused by thioridazine affects the differentiation of glial cells via the changes in membrane properties.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed1995

Effect of haematoporphyrin-induced photosensitization on lipid membranes.

In vitro cultured mouse myeloma (Sp-2/0-Ag14) cells and phosphatidylcholine liposomes were used to study the membrane effects of photosensitization with an He-Ne laser activated haematoporphyrin (HP). Lipophilic HP molecules, intercalated between the membrane lipid molecules, caused morphological changes of cell membranes on light activation. Steady state and time-resolved fluorescence spectroscopic studies of membrane-bound HP molecules provide information about the change in membrane lipid dynamics (fluidity). Increased HP fluorescence anisotropy was found after laser irradiation in the case of cell membrane. This finding can be related either to the increased rotation correlation time of the rotating fluorophore (HP) (decreased membrane fluidity) or to the decrease in the angular range of molecular rotation, which corresponds to an increased lipid order after photosensitization. Changes in the ratio of saturated:unsaturated fatty acid content of membrane lipids or other chemical events such as cross-linking of membrane components during the photosensitization process can also account for the observed effects.

Animals↗
PubMed1997

Artemisinin enhances heme-catalysed oxidation of lipid membranes.

Artemisinin, a sesquiterpene endoperoxide derived from a traditional Chinese herbal remedy for fevers, is a promising new antimalarial drug, particularly useful against multidrug resistant strains of P. falciparum. Despite widespread clinical use, its mode of action remains uncertain. We investigated whether its antimalarial properties could be explained by an ability to enhance the redox activity of heme, formed in the parasite food vacuole from digested hemoglobin. Artemisinin caused a sustained threefold increase, followed by a gradual decline, in the peroxidase activity of heme. It also enhanced the ability of heme to oxidize membrane lipids about sixfold. An unexpected finding was the potentiation of heme-catalysed membrane lipid oxidation by Vitamin E. The changes in redox-catalytic activity induced by artemisinin were paralleled by major changes in the absorption spectrum of heme, culminating in loss of the Soret band. We propose a model in which artemisinin binds irreversibly to heme in the parasite food vacuole, preventing its polymerization to chemically inert hemozoin, and promoting heme-catalysed oxidation of the vacuolar membrane by molecular oxygen, which leads, ultimately, to vacuole rupture and parasite autodigestion.

Antimalarials↗
PubMed1999

Dual interaction of ADP ribosylation factor 1 with Sec7 domain and with lipid membranes during catalysis of guanine nucleotide exchange.

Sec7 domains catalyze the replacement of GDP by GTP on the G protein ADP-ribosylation factor 1 (myrARF1) by interacting with its switch I and II regions and by destabilizing, through a glutamic finger, the beta-phosphate of the bound GDP. The myristoylated N-terminal helix that allows myrARF1 to interact with membrane lipids in a GTP-dependent manner is located some distance from the Sec7 domain-binding region. However, these two regions are connected. Measuring the binding to liposomes of functional or abortive complexes between myrARF1 and the Sec7 domain of ARNO demonstrates that myrARF1, in complex with the Sec7 domain, adopts a high affinity state for membrane lipids, similar to that of the free GTP-bound form. This tight membrane attachment does not depend on the release of GDP induced by the Sec7 domain but is partially inhibited by the uncompetitive inhibitor brefeldin A. These results suggest that the conformational switch of the N-terminal helix of myrARF1 to the membrane-bound form is an early event in the nucleotide exchange pathway and is a prerequisite for a structural rearrangement at the myrARF1-GDP/Sec7 domain interface that allows the glutamic finger to expel GDP from myrARF1.

ADP-Ribosylation Factor 1↗
PubMed1979

Membrane damage by a toxin from the sea anemone Stoichactis helianthus. II. Effect of membrane lipid composition in a liposome system.

In the first paper of this series, it was shown that a toxin from the sea anemone Stoichactis helianthus increased the permeability of black lipid membranes due to transmembrane channel formation. In the present study, we have used liposomes to examine the reactivity of the toxin with different phospholipids. Membrane damage was assessed by measuring the release of 86Rb+ and 14C-labeled membrane lipid. For the different lipids, the rank order of marker release was: sphingomyelin greater than C18 : 2 phosphatidylcholine greater than C18 : 1 phosphatidylcholine greater than C18 : 0 phosphatidylcholine greater than C16 : 0 phosphatidylcholine = C14 : 0 phosphatidylcholine. In C14 : 0 and C16 : 0 phosphatidylcholine liposomes there was no 14C-labeled lipid release and only 13 to 16% 86 Rb+ release which corresponds to the 86Rb+ content in the outermost aqueous shell of multilamellar liposomes. This indicates that membrane damage was limited to the outermost bilayer. In liposomes prepared with the other lipids, the extent of release of both markers increased proportionately with the length and the degree of unsaturation of the lipids' acyl side chains. Spingomyelin liposomes were the most susceptible with 47% of the 14C-labeled lipid marker and 90% of the 86Rb+ marker being released. The large extent of 14C-labeled lipid release is attributed to a detergent-like activity of the toxin which presumably is due to the amphipathic nature of the protein. Thus, the toxin can inflict membranrtance of one mechanism or the other apparently varies depending on membrane structure and lipid composition.

Cholesterol↗
PubMed1994

Permeability and electrical properties of planar lipid membranes from thylakoid lipids.

Electrical measurements were carried out on planar lipid membranes from thylakoid lipids. The specific capacitance of membranes formed from decane-containing monogalactosyldiacylglycerol (MGDG), which accounts for 57% of the total lipid content of thylakoids, showed that it adopted a bilayer structure. Solvent-free bilayers of MGDG were not formed, with very rare exceptions, indicating that decane is required to stabilize the planar conformation. However, this cone-shaped lipid produces bilayer structures in combination with other cylindrical thylakoid lipids even in the absence of organic solvent. We compared the properties of solvent-free and decane-containing bilayers from MGDG, soybean lecithin, and the quaternary mixture of lipids similar to that found in vivo. The conductance of decane-MGDG was 26 times higher than that of decane-lecithin. The flux through the decane-lecithin bilayer was found to be slightly dependent on pH, whereas the decane-MGDG membrane was not. The specific conductance of bilayers formed from the quaternary mixture of lipids was 5 to 10 times larger than lecithin (with alkane or not). Further experiments with bilayers made in the presence of a KCl gradient showed that decane-MGDG, decane-MGDG/DGDG/SQDG/PG, and solvent-free MGDG/DGDG/SQDG/PG were cation-selective. The permeability coefficient for potassium ranged from 4.9 to 8.3 x 10(-11) cm s-1. The permeability coefficient for protons in galactolipids, however, was determined to be about six orders of magnitude higher than the value for potassium ions. The HCl permeation mechanism through the lipid membranes was determined from diffusion potentials measured in HCl gradients. Our results suggest that HCl was not transported as neutral molecules. The data is discussed with regard to the function of galactolipids in the ion transport through thylakoid membranes.

Alkanes↗