Pressure effect on reversed micelles in water: An infrared spectroscopic study of aqueous dioleoyl phosphatidylethanolamine

Phases and phase transitions of the hydrated phosphatidylethanolamines

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Here, a review of the LIPIDAT data subset referring to hydrated phosphatidylethanolamines (PE) is presented together with an analysis of these data. The PE subset represents 14% of all LIPIDAT records. It includes data collected over a 38-year period and consists of 1511 records obtained from 203 articles in 35 different journals. An analysis of the data in the subset has allowed us to identify trends in synthetic PE phase behavior reflecting changes in lipid chain length, chain unsaturation (number, isomeric type and position of double bonds), chain asymmetry and branching, type of chain-glycerol linkage (ether vs. ester) and headgroup modification. Also included is a summary of the data concerning the effect of pH, stereochemical purity, and different additives such as salts, saccharides, alcohols, amino adds and alkanes on PE phase behavior. Information on the phase behavior of biologically derived PE is also presented. This review includes 236 references.

Is the mechanism of general anesthesia related to lipid membrane spontaneous curvature?

Lipid bilayers in biomembranes may exist in a state of elastic curvature stress which may couple to the conformation of integral membrane proteins in a logical, and energetically significant, fashion. Many biomembranes contain sufficiently large fractions of nonlamellar-prone lipids to have monolayers under substantial curvature stress. Although very few experiments have been performed that can be used to correlate protein activity with curvature stress, the literature does contain a small number of studies that indicate that some protein function is nonspecifically modulated by the amounts of nonlamellar-prone lipid in the imbedding bilayers. The spontaneous curvature, is altered by the presence of anesthetics in physiologically relevant concentrations. This leads us to suggest that anesthetic action may be coupled to protein function via alteration of the tensions leading to the spontaneous curvature of biomembrane layers. The spontaneous curvature is also sufficiently sensitive to pressure that a mechanism for the pressure reversal of anesthesia follows if the effects of pressure are to counter changes in membrane lateral tension induced by anesthetics. It is emphasized that many more experimental data must be acquired to determine whether the ideas presented in this paper have validity. In particular, there is a need for data on the effects of different anesthetics and pressure on the spontaneous curvature and, more generally, lipid monolayer lateral tensions. Most importantly, experiments must be performed to investigate whether protein function correlates with these quantities.

Orientation studies of hydrated dipalmitoylphosphatidylcholine multibilayers by polarized FTIR-ATR spectroscopy

Polarized Fourier-transform infrared-attenuated total reflection spectroscopy has been applied to explore the temperature-dependence of molecular orientations in multibilayers of 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) of various degrees of hydration. The order parameter of the hydrocarbon chain, evaluated from the dichroic ratios of the antisymmetric and symmetric CH2 stretching bands, was drastically decreased at the main (or gel to liquid-crystalline phase) transition temperature (Tm) irrespective of the water content, suggesting that the hydrocarbon chain is in a disordered state as a result of chain-melting associated with an increase in the number of the gauche conformers. On the other hand, the dichroic ratios of the polar bands of hydrated DPPC assignable to the symmetric PO2- stretching and asymmetric N+ (CH3)3 stretching modes were increased mainly at the pretransition temperature (Tp), except for less hydrated case. The dichroic ratios of both the OH stretching and OH2 bending bands of water showed the same temperature-dependence as those of the polar bands. These results indicate that the pretransition is ascribable mainly to the reorientation of the polar groups of the DPPC and bound water, while the main transition is due to the orientational disorder of the hydrocarbon chains. For less hydrated DPPC, the reorientation of the polar groups and water did not occur around Tp, but in the higher temperature region around Tm. This is in accord with the previously reported observation that the pretransition disappears for less hydrated DPPC. In this case, the polar groups and water may reorient following the reorientation of the hydrocarbon chains near Tm.

High-pressure infrared study of phosphatidylserine bilayers and their interactions with the local anesthetic tetracaine

High-pressure Fourier-transform infrared (FT-IR) spectroscopy was used to study the barotropic behavior of phosphatidylserine bilayers and their interactions with the local anesthetic tetracaine. The model membrane systems studied were multilamellar aqueous dispersions of 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) and 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) in the absence and the presence of tetracaine at pH 5.5 and 9.5. The infrared spectra were measured at 28 degrees C in a diamond anvil cell as a function of pressure up to 25 kbar. The results show that the barotropic behavior of the negatively charged phosphatidylserine bilayers is very similar to that observed for zwitterionic phospholipids, such as phosphatidylcholine and phosphatidylethanolamine, with corresponding acyl chains. The results also indicate that the local anesthetic partitions into phosphatidylserine bilayers in an environment close to the membrane-water interface and interacts electrostatically with the lipid head group. Application of high hydrostatic pressure on the lipid-anesthetic systems results in the pressure-induced expulsion of the anesthetic from a membrane to an aqueous environment. The pressures required for expulsion of anesthetic from bilayers are much higher for the unsaturated lipid (DOPS) than for the saturated lipid (DMPS) (approximately 6 kbar vs approximately 2 kbar, respectively). Whereas incorporation of the anesthetic into DOPS bilayers does not affect significantly the structural and dynamic properties of the disordered acyl chains in the liquid-crystalline phase, it orders the DMPS acyl chains in the gel phase.

Fluorescence depolarization study on non-bilayer phases of phosphatidylethanolamine and phosphatidylcholine lipid mixtures

The orientational order and rotational dynamics of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5- hexatrienyl)phenyl]ethyl] carbon yl]-3-sn-phosphatidylcholine (DPH-PC) in dilinoleoylphosphatidylethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) 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 (0-5% PC) phases. As the lipids changed from the lamellar to intermediate phase, the order parameter increased at all temperatures (1-50 degrees C). On the contrary, the rotational diffusion decreased at high temperatures (20-50 degrees C) but increased at low temperatures (1-10 degrees 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.