Lipid concentration affects the kinetic stability of dielaidoylphosphatidylethanolamine bilayers (original) (raw)
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Chemistry and Physics of Lipids, 1989
The orientational order and rotational dynamics of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-l,3,5-hexatrienyl)phenyl]ethyl] carbon yl]-3-sn-phosphatidylchofine (DPH-PC) in dilinoleoylphosphatidylethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine 0aOPC) binary lipid mixtures were investigated. A previous study (Biochim. Biophys. Acta 731 (1983) 177) indicated that the empirical phase diagram of POPC/DLPE can roughly be divided into three zones. They are the lamellar (15% PC and higher), intermediate (5-15% PC) and inverted hexagonal (0-50/0 PC) phases. As the lipids changed from the lamellar to intermediate phase, the order parameter increased at all temperatures (1-50°C). On the contrary, the rotational diffusion decreased at high temperatures (20-50°C) but increased at low temperatures (I-10°C). These results indicate that the intermediate phase is in a stressed state at high temperatures but in a highly mobile amorphous state at low temperatures. As the lipid progressed from the intermediate toward hexagonal phase, the order parameter decreased abruptly at all temperatures. The ratio of order parameter in the intermediate phase to that in the hexagonal phase was calculated. This ratio was found to increase linearly with temperature, indicating that a distinct change in the packing symmetry of lipids occurred as temperature increased. From the intermediate to hexagonal phase, the rotational diffusion increased slightly at high temperatures but declined abruptly at low temperatures. These results further agreed with the stressed and amorphous natures of the intermediate phases as described above.
The effect of temperature on lipid-n-alkane interactions in lipid bilayers
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1986
The partitioning of n-alkanes between an egg-phosphatidylcholine bilayer and its toms was studied for alkanes with ten to sixteen carbon atoms using measurements of membrane capacitance. The partition coefficient was found to decrease with increasing alkane chainlength and to increase with increasing temperature. This is consistent with a well-known statistical model of lipid alkane bilayers in the liquid crystalline state. It was found that n-decane was unsuitable as a solvent in these experiments because significant partitioning of n-decane into the aqueous phase and atmosphere occurred and this could not be adequately controlled. Egg-phosphatidylcholine bilayers containing negligible amounts of solvent could be produced using a method similar to the 'freeze-out' method of White (Biochim. Biophys. Acta 356 (1974) 8-16). Bilayers formed using n-hexadecane were found to be virtually solvent-free at temperatures below 30°C. The partition coefficient of n-alkanes in the bilayer was also found to depend on the alkane mole fraction. Thus it was concluded that the assumption of ideal mixing between acyl and aikane chains in the bilayer was not valid when the alkane mole fraction exceeded 40% (with respect to the acyl chains of the lipid). The variation of the standard chemical potential with temperature was measured for alkanes of different chainlengths and it was concluded that the enthalpy and entropy of the alkanes in the bilayer are in themselves temperature-dependent. This indicates that the state of the hydrophobic interior of lipid bilayers varies with temperature.
Chemistry and Physics of Lipids, 1994
The bilayer stability of liposomes containing unsaturated phosphatidylethanolamine (PE) has been investigated by measuring the C~O and CH 2 stretching frequencies of the lipids at different lipid compositions and temperatures. Binary mixtures of 1-palmitoyl-2-oleoylphosphatidyleholine (POPC) and dilinoleoyl-PE (DLPE) are known to exhibit lamellar liquid crystalline (L,), inverted hexagonal (Hn) and metastable intermediate (I) phases. Abrupt increases in the C~-O and CH2 stretching frequencies at 65-75 and 90-95% PE, respectively, were found as the PE content of the DLPE/POPC mixtures was increased from 0 to 100%. These transitions were associated with the La-I and I-HII phase transitions of the DLPE/POPC mixtures, accordingly. The effects of three lipid perturbants, butylated hydroxytoluene (BHT), diacylglyeerol (DG) and cholesterol (CL), on the above L~-I and I-H n transitions were also examined. All perturbants were found to be effective in shifting the L~-I transition of the DLPC/POPC mixtures to a lower PE% as detected by the C=O stretching frequency measurements. On the other hand, the perturbants appeared to eliminate the I-Hn transition of the DLP~POPC mixtures as detected by the CH2 stretching frequency measurements. The effectiveness of the perturbants in promoting the La-I phase transition of the DLPE/POPC mixtures followed the order of DG > BHT > CL. The phase boundaries of this L~-I transition at different lipid and perturbant compositions were further quantitated by the use of three-dimensional contour plots (Cheng, Chem. and Phys. Lipids, 60, 119-125 (1991)) of the C~O frequency as a function of DLPE/POPC and perturbant/lipid compositions. It was concluded that the lipid C=O vibrational frequency is a useful and non-invasive parameter for examining the bilayer stability of liposomes.
Biochemistry, 1987
Cholesterol lowers the bilayer to hexagonal phase transition temperature of phosphatidylethanolamines up to a mole fraction of about 0.1. At cholesterol mole fractions above about 0.3, the effect of this sterol is to stabilize the bilayer phase. The relatively weak effects of cholesterol in altering the bilayer to hexagonal phase transition temperature can be explained on the basis of lateral phase separation. This is indicated by the horizontal liquidus line for the gel to liquid-crystalline transition in the phase diagram for mixtures of cholesterol with dielaidoylphosphatidylethanolamine (DEPE) as well as the fact that cholesterol does not greatly decrease the cooperativity of the bilayer to hexagonal phase transition. The enthalpy of this latter transition increased with increasing mole fractions of cholesterol. Two oxidation products of cholesterol are 5-cholesten-3P,7a-diol and cholestan-3P,5a,6P-triol. Compared with cholesterol, 5-cholesten-3@,7a-diol had a greater effect in decreasing the bilayer to hexagonal phase transition temperature and broadening this transition. It is suggested that its effectiveness is due to its greater solubility in the DEPE. In contrast, cholestan-3P,5a,6P-t1.iol raises the bilayer to hexagonal phase transition temperature of DEPE. This is due to its larger and more hydrophilic head group. In addition, its length, being shorter than that of DEPE, would not allow it to pack efficiently in a hexagonal phase arrangement. We suggest that this same effect is responsible for cholesterol raising the bilayer to hexagonal phase transition temperature at higher mole fractions.
Metastability in the phase behavior of dimyristoylphosphatidylethanolamine bilayers
Biochemistry, 1984
A new subgel phase is demonstrated to occur in hydrated dimyristoylphosphatidylethanolamine (DMPE) by using dilatometric and calorimetric techniques. The formation of the subgel phase takes place very slowly at temperatures near 0 OC, but it can still be observed at 25 "C. Once formed, the subgel phase melts (AHh = 16.0 f 0.6 kcal/mol and AV = 0.085 f 0.014 mL/g) directly into the liquid-crystalline phase at a temperature, Th = 56.3 OC, that is higher than the Low-temperature phases in phospholipid bilayers and the phase transitions into such phases are important references with which to compare the biologically relevant high-temperature phase, La, and from which to obtain quantitative information concerning the molecular interactions that determine bilayer structure . The gel to liquid-crystalline transition temperature, T , = 49.6 "C. Thus, the gel phase appears to be metastable over its entire temperature range. In this regard, DMPE behaves differently from dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine but similarly to dilaurylphosphatidylethanolamine. This unusual long-lived metastability provides cells an additional option in determining the properties of membranes. discovery by Chen and co-workers of the subtransition in saturated phosphatidylcholines having 16, 17, or 18 carbons per chain has been followed by some detailed studies of the kinetics of formation and the density of the new subgel phase and by structural studies of the subgel phase using diffraction and spectroscopy (Fuldner,
Biochemistry Usa, 1988
The effect el mono., di. and triaeyiglyeerols on the bilayer to hexagonal phase (1-1 n) transition was studied by. differential sc~min 8 calerimetry and StP.NMR spectresce~. The acylglycemls were mixed with either dlelaidoyl~ylethanoline or with l.palmitoyl-2.oleeyll~letbmohmine. Acylglycerols of laurie, olek and shmrte acids were mgized. All el the aeylglyeerols lowered the bilayer to H u phase transition ~. Diaeylglycerols were much better H n phase promoters than monoacylglycerois while ~aeylglyee~,~ were the most potent Mlayer plme destabilizers. Fatty acid ~fiea geaer'dly bad less el an effect except for the memaeylglyeemb where bilayer destal~ inmmsed from monoludn to monostezdn to mommlein. 'lee meat marked difference in bebaviom' resul~ from ckanges in the hay acid mnpesition el ee tcy~ycerol occumd with tristeadn. This was tie only acyl~ycerol wMcb decreased the b~ycr to H a phi,, transition temperature only below a tool fraction el 0.005. Above this reel fraction, further addJfion of trlsteadn had no dfect on the bi~yer to H n phase transition. These results suggest that the tristearin im limited solul~ty hi phmphatidylethanolmlne.
Effect of Physical Parameters on the Main Phase Transition of Supported Lipid Bilayers
Biophysical Journal, 2009
Supported lipid bilayers composed of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) and 1-palmitoyl-2oleoyl-phosphatidylglycerol (POPG) were assembled by the vesicle fusion technique on mica and studied by temperaturecontrolled atomic force microscopy. The role of different physical parameters on the main phase transition was elucidated. Both mixed (POPE/POPG 3:1) and pure POPE bilayers were studied. By increasing the ionic strength of the solution and the incubation temperature, a shift from a decoupled phase transition of the two leaflets, to a coupled transition, with domains in register, was obtained. The observed behavior points to a modulation of the substrate/bilayer and interleaflet coupling induced by the environment and preparation conditions of supported lipid bilayers. The results are discussed in view of the role of different interactions in the system. The influence of the substrate on the lipid bilayers, in terms of interleaflet coupling, can also help us in understanding the possible effect that submembrane elements like the cytoskeleton might have on the structure and dynamics of biomembranes.
Gauging the Effect of Impurities on Lipid Bilayer Phase Transition Temperature
The Journal of Physical Chemistry B, 2006
We report on the gel-to-fluid phase transition behavior of unilamellar vesicles formed with 1,2-dimyristoylsn-phosphatidylcholine (14:0 DMPC). We have interrogated the gel-to-fluid transition temperature of these bilayer structures using the chromophore perylene incorporated in their nonpolar region. We observe a discontinuous change in the reorientation time of perylene sequestered within the bilayer at the known melting transition temperature of 14:0 DMPC, 24°C. The perylene reorientation data reveal a local viscosity of 14.5 (2.5 cP in the gel phase, and 8.5 (1.5 cP in the fluid phase. We have also incorporated small amounts of 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (14:1 DMPC) into these unilamellar vesicles and find that the melting transition temperature for these bilayers varies in a regular manner with the amount of 14:1 DMPC present. These data demonstrate that very little "contaminant" is required to cause a substantial change in the gel-to-fluid transition temperature, even though these contaminants do not alter the viscosity of the bilayer sensed by perylene, either above or below the melting transition.
Biochemistry, 1990
The quadrupolar splitting profiles of methylene groups along the acyl chains of perdeuteriated dimyristoylphosphatidylcholine (DMPC-dS4) in mixtures with dioleoylphosphatidylethanolamine (DOPE) were studied by 2H N M R. The quadrupolar splittings, obtained for lipid mixtures in the bilayer state, were measured as functions of temperature and PE:PC ratio and were used to obtain the approximate gauche probabilities a t a given chain position, pB. Ratios (R) ofpB for C13, C12, and C1 1 relative to that of the plateau region were used to characterize the effect of increasing P E on the gauche content of PC chains. At all temperatures studied (including the bilayer to hexagonal phase transition region), for each ratio R (e.g., RC13,P), the relative gauche content of the D M P C chains was similar over the range of 2 5 4 5 % PE. DOPE is viewed in simple terms as having a "conical" shape; if this geometry applies to the acyl chain region of the molecule, a greater lateral pressure would be expected toward the center of the bilayer as the P E content is increased, resulting in a decreased gauche content, relative to the plateau, of those methylene groups of PC. The failure to observe the predicted increase in lateral pressure has ramifications for the cone-shape molecular model. The overall "cone shape" of P E is seen to arise from the smaller size of the head-group relative to the acyl chains; however, the acyl chain region itself is not rigidly cone-shaped and is better represented by a flexible ''balloon''. These results were supported by small-angle X-ray diffraction, which showed a decreasing trend in the area per molecule with increasing P E content.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1988
The effect el mono., di. and triaeyiglyeerols on the bilayer to hexagonal phase (1-1 n) transition was studied by. differential sc~min 8 calerimetry and StP.NMR spectresce~. The acylglycemls were mixed with either dlelaidoyl~ylethanoline or with l.palmitoyl-2.oleeyll~letbmohmine. Acylglycerols of laurie, olek and shmrte acids were mgized. All el the aeylglyeerols lowered the bilayer to H u phase transition ~.