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PubMed1983

Protein-mediated lipid transfer. The effects of lipid-phase transition and of charged lipids.

The protein-mediated phospholipid exchange between small unilamellar vesicles was investigated by fluorescence polarization measurements with diphenylhexatriene as optical probe. Thermotropic phase-transition measurements were taken after mixing two vesicle preparations of distinct and different phase-transition temperatures or having different states of charge. From the heights of each phase-transition step, we were able to follow the lipid-exchange process in the presence, as well as in the absence (natural exchange), of so-called transfer protein isolated from beef liver. A strong enhancement of the lipid transfer was observed at the corresponding lipid-phase-transition temperature, which is explained by the presence of fluctuating fluid and ordered domains co-existing at the lipid-phase-transition temperature. A unidirectional lipid transfer of the neutral component was observed between negatively charged phosphatidic acid and neutral phosphatidylcholine vesicles. Fluorescence polarization measurements showed the disappearance of the phosphatidylcholine phase transition, whereas the phosphatidic acid phase transition broadened and its phase transition temperature became lower.

Androgen-Binding Protein↗

PubMed1978

The effect of free fatty acids on the thermotropic phase transition of dimyristoyl glycerophosphocholine.

The effect of free fatty acids on the phase transition characteristics and fluidity of bilayers of dimyristoyl glycerophosphocholine were studied by pyrene eximer fluorescence and differential scanning calorimetry. High melting saturated fatty acids with chain lenghts of 12--18 carbon atoms raise the phase transition temperature and enhance the ability of pyrene to form clusters in the gel state while not affecting the fluidity of the membrane in the liquid crystal state. Low melting unsaturated fatty acids lower the phase transition temperature and decrease the ability of pyrene to form clusters in the gel state while not affecting the fluidity of the membrane in the liquid crystal state. The effects of the very long chain fatty acids, arachidic (C 20) and behenic (C 22) appears to be similar to those of cholesterol in that they cause a broadening of the phase transition with a lowering of the transition enthalpy but have little effect on the temperature at which the phase transition occurs.

Calorimetry↗

PubMed1982

Fluorescence depolarization studies of the phase transition in multilamellar phospholipid vesicles exposed to 1.0-GHz microwave radiation.

The phase transition in multilamellar dimyristoylphosphatidylcholine (DMPC) vesicles was studied during exposure to continuous wave 1.0-GHz microwave radiation. Fluorescence depolarization measurements using a lipid-seeking molecular probe, diphenylhexatriene (DPH), were performed as a function of temperature. Semilog plots of microviscosity versus temperature illustrate the phase transition which shows a 5 degree C shift when the vesicles are treated with chloroform as a positive control. No shift of the phase transition was found during exposure to microwave radiation at specific absorption rates between 1 and 30 W/kg. Samples were exposed in a rectangular transmission line (TEM cell), and specific absorption rates were calculated from electrical measurements of incident, reflected, and transmitted power. Samples were exposed to increasing intensities of radiation, while the temperature was maintained at either 23.5 or 25.5 degree C; these temperatures represented the two ends of the phase transition region for these vesicles. No statistically significant difference was found between exposed and control samples. These results are in contrast to those of others using laser Raman spectroscopy to measure the phase transition in similar multilamellar vesicles exposed to microwave radiation.

Dimyristoylphosphatidylcholine↗

PubMed1978

Studies on the effect of the lipid phase transition on the interaction of glucagon with dimyristoyl glycerophosphocholine.

Glucagon is found to interact with dimyristoyl glycerophosphocholine both above and below the phase transition temperature of the lipid. Above the phase transition temperature the interaction is manifested by an increase in the rate of vesicle aggregation and by an increased permeability of unilamellar vesicles to Eu3+ and to Fe(CN)3-6. However, no stable lipoprotein complex can be detected by gel filtration. Below the phase transition glucagon can form stable complexes with dimyristoyl glycerophosphocholine vesicles but cannot rapidly rearrange these vesicles to disk-shaped particles until the phase transition temperature is approached. The energy of activation for the dissociation of glucagon from the disk-shaped lipoprotein particle is 29 kcal/mol at temperatures above 36 degrees C but increases markedly at lower temperatures, as the region of the lipid phase transition is approached. This increase in energy of activation at lower temperatures is most probably due to the larger amount of energy required to rearrange gel-state lipid in the transition state and provides an explanation for the unusual kinetic stability of the glucagon-dimyristoyl glycerophosphocholine lipoprotein complex only at temperatures below the phase transition of the lipid.

Chemical Phenomena↗

PubMed1974

Electrostatic effects on lipid phase transitions: membrane structure and ionic environment.

Ordered --> fluid phase transitions in bilayers of charged lipids are accompanied by a decrease in electrostatic free energy mainly as a result of bilayer expansion. For uniform charge distribution the Gouy-Chapman theory of the electrical double layer predicts a decrease of the transition temperature with increasing charge density. We studied the effects of pH and mono- and divalent cations on the phase transition of lecithin, cephalin, phosphatidylserine, and phosphatidic acid bilayers. Phosphatidic acid with two ionizable protons was selected for a systematic investigation. A change in pH from 7 to 9 increases the charge per polar group from one to two elementary charges. This lowers the transition temperature by about 20 degrees C in agreement with the theory. In this pH region rather small changes in pH suffice to induce the phase transition at constant temperature. Divalent cations (Mg(++) and Ca(++)) increase the transition temperature by charge neutralization and thus can be used to induce the fluid --> ordered transition at constant temperature. In contrast, monovalent cations (Li(+), Na(+), K(+)) lower the transition temperature, or fluidize the bilayer structure at a given temperature. Rather small changes in ionic environment can induce gross alterations in bilayer structure; divalent and monovalent cations have antagonistic effects. This result parallels current theories on nerve excitation and sensory transduction where cation-induced structural changes in biomembranes are invoked.

Calcium↗

PubMed1987

Modulation of the phase transition behavior of phosphatidylethanolamine by cholesterol and oxysterols.

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-3 beta,7 alpha-diol and cholestan-3 beta,5 alpha,6 beta-triol. Compared with cholesterol, 5-cholesten-3 beta,7 alpha-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-3 beta,5 alpha,6 beta-triol 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.

Cholesterol↗

PubMed1988

pH-dependent phase transition of chlorpromazine micellar solutions in the physiological range.

The effects of pH and drug concentration on aggregation properties of chlorpromazine-HCl (CPZ) are examined. The critical micelle concentration (cmc) changes from 0.2 mM at pH 7.3 to 2 mM at pH 5.6 as estimated from the stearic acid spin label solubility measurements. For concentrations above the cmc CPZ micelles undergo a concentration-, temperature- and pH-dependent transition leading to phase separation. This phase transition is followed by a sudden increase of light scattering. The phase diagram pH vs. concentration is obtained by observation of the cloud point for concentrations ranging from 0.01 to 10 mM. The intramicellar environment is probed at pH ranging from 5.5 to 8.0 using a stearic acid spin label. The intramicellar compactness increases smoothly with increasing pH suggesting the weakening of polar heads repulsion due to charge decrease. The reported results indicate that pH effects are relevant and should be properly taken into account in the performance and interpretation of experiments with CPZ.

Chlorpromazine↗

PubMed1980

Phase transitions of alkyl ether analogs of phosphatidylcholine.

The phase-transition temperatures of aqueous dispersions of diester, monoether and diether analogs of phosphatidylcholine were determinmed using transparinaric acid as a fluorescent probe. The diether analog of phosphatidylcholine has a higher phase-transition temperature, whilst the monoether analog has a lower phase-transition temperature than their diester counterpart.

Liposomes↗

PubMed1984

Effect of phase transitions on the interaction of peptides and proteins with phospholipids.

This review is not a comprehensive study of the broad area of lipid-protein interactions, but rather concentrates on the question of the effect of phase transitions on the interaction of peptides and proteins with phospholipids. Before considering the relative ability of peptides and proteins to incorporate into phospholipid bilayers in the gel or the liquid crystalline state, we briefly review the variety of effects of proteins on lipid phase transitions. It is essential to be cognizant of these effects when discussing how phase transitions affect protein incorporation. The effect of proteins on lipid order and motion above and below the phase transition is discussed and the current state of knowledge on this topic is briefly reviewed. In discussing the thermodynamics of lipid-protein association and the effect of phase transitions one must deal with systems at equilibrium, a state often difficult to achieve with high molecular weight aggregates. It is demonstrated that there are a variety of effects of phase transitions on protein incorporation. Some proteins incorporate more readily into liquid crystalline state lipid; others incorporate only in a narrow temperature region around the phase transition temperature, while still others interact with lipid over a broad range of temperatures while exhibiting some preference for interacting with gel state lipid. The molecular basis for preferential interaction with gel state lipid is suggested to be the ability of proteins to self-associate, probably at defect sites, below the phase transition temperature and thereby increase protein-protein interactions while maintaining protein-lipid and lipid-lipid interactions.+

Kinetics↗

PubMed1987

Phase transitions in sequence matches and nucleic acid structure.

Analyses of phase transitions in biopolymers have previously been restricted to studies of average behavior along macromolecules. Extremal properties, such as longest helical region, can now be studied with a new family of probability distributions [Arratia, R., Gordon, L. & Waterman, M. S. (1986) Ann. Stat. 14, 971-993]. Not only is such extremal behavior analyzed with great precision, but new phase transitions are determined. One phase transition occurs when behavior of the free energy of the longest helical region abruptly changes from proportional to sequence length. The annealing of two single-stranded molecules and the melting of a double helix are both considered. These results, initially suggested by studies of optimal matching of random DNA sequences [Smith, T. F., Waterman, M. S. & Burks, C. (1985) Nucleic Acids Res. 13, 645-656], also have importance for significance tests in comparison of nucleic acid or protein sequences.

Base Sequence↗

PubMed1988

Structures and mechanisms of lipid phase transitions in nonaqueous media. Dipalmitoylphosphatidylethanolamine in fused salt.

The phase transitions for dipalmitoylphosphatidylethanolamine (DPPE) dispersed in water and in N-ethylammonium nitrate (EAN) were examined using differential scanning calorimetry and time-resolved x-ray diffraction. Subgel, pre-, and main-phase transitions were observed for DPPE in water, whereas only the pre- and main transitions were observed for DPPE in EAN. Hysteresis was observed for both dispersions upon cooling. In addition, the lamellar (L alpha) to hexagonal (H alpha) phase transition was observed for DPPE dispersed in EAN when using time-resolved x-ray diffraction but not when using calorimetry. This low enthalpy process occurred at 73-77 degrees C, which is significantly lower than that observed for DPPE in water. The presence of EAN stabilizes the existence of the H alpha phase in DPPE by its influence on the bilayer interfacial properties, primarily on the area per lipid head group.

Calorimetry, Differential Scanning↗

PubMed1987

Dynamic properties of the haptenic site of lipid haptens in phosphatidylcholine membranes. Their relation to the phase transition of the host lattice.

The relation between the dynamic properties of the haptenic site of lipid haptens and the phase transition of the host lattice was investigated using head group spin-labeled phosphatidylethanolamines, that is, spin-label lipid haptens (Brûlet, P., and H. M. McConnell, 1976, Proc. Natl. Acad. Sci. USA., 73:2977-2981; Brûlet, P., and H. M. McConnell, 1977, Biochemistry, 16:1209-1217). The electron spin resonance (ESR) spectra of the lipid haptens in liposomal membranes showed three narrow resonance lines, whose widths and hyperfine splitting values suggested that the haptenic site, i.e., the spin-label moiety, should be exposed in the water phase. The line width of each peak depended on the host lipid species and on the incubation temperature. A temperature study using dipalmitoylphosphatidylcholine (DPPC) liposomes showed that the dynamic properties of the haptenic site were related to the main phase transition and the subphase transition of the host lattice but not to the prephase transition. The angular amplitudes of the tumbling motion of the haptenic site were estimated using oriented multibilayer systems. The angular amplitude of dipalmitoyl-phosphatidyl-N-[[N-(1-oxyl-2,2,6, 6-tetramethyl-4-piperidinyl)-carbamoyl]-methyl]-ethanolamine in DPPC membranes was 63 degrees at 2 degrees C, and it increased slightly with an increase in temperature regardless of the phase transition of the host lattice. The value for egg phosphatidylcholine (PC) at 25 degrees C was the same as for DPPC above its main phase transition temperature. Rotational correlation time analysis showed that the axial rotation of the haptenic site was preferable to the tumbling motion of the rotational axis, and the predominance depended on the phase transition, Lc----L beta' and P beta'----L alpha. Elongation of the spacer arm between the haptenic site and phosphate increased the angular amplitude of the tumbling motion but reduced the effect of the host lattice. Spin-label lipid haptens with unsaturated fatty acyl chains were distributed heterogeneously in DPPC membranes, whereas those with the same fatty acyl chain as the host lattice were distributed randomly. The ESR spectrum of a lipid hapten under its prephase transition temperature showed two components, broad and narrow. This suggests that at least two different domains, a hapten-rich domain and a hapten-poor one, may coexist in membranes. ESR measurements at various temperatures suggested that the haptenic site fraction in the hapten-rich domain decreased in part during the phase transition from L beta' to P beta', and disappeared completely in the La phase. The spatial mobility and lateral diffusion of lipid haptens will be discussed in greater detail.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

A solid-solution theory of anesthetic interaction with lipid membranes: temperature span of the main phase transition.

Anesthetics (or any other small additives) depress the temperature of the main phase transition of phospholipid bilayers. Certain anesthetics widen the temperature span of the transition, whereas others do not. The widening in a first-order phase transition is intriguing. In this report, the effects of additive molecules on the temperature and its span were explained by the solid-solution theory. By assuming coexistence of the liquid-crystal and solid-gel phases of lipid membranes at phase transition, the phase boundary is determined from the distribution of anesthetic molecules between the liquid-crystal membrane versus water and between the solid-gel membrane versus water. The theory shows that when the lipid concentration is large or when the lipid solubility of the drug is large, the width of the transition temperature increases, and vice versa. Highly lipid-soluble molecules, such as long-chain alkanols and volatile anesthetics, increase the width of the transition temperature when the lipid:water ratio is large, whereas highly water-soluble molecules, such as methanol and ethanol, do not. The aqueous phase serves as the reservoir for anesthetics. Depletion of the additive molecules from the aqueous phase is the cause of the widening. When the reservoir capacity is large, the temperature width does not increase. The theory also predicts asymmetry of the specific heat profile at the transition.

Anesthetics↗

PubMed1981

Influence of dicarboxylic phosphatidylcholines on the stability and phase transition of phosphatidylcholine liposomes.

The effect of dicarboxylic phosphatidylcholines (glutaryl phosphatidylcholine) on the stability and phase transition of phosphatidylcholine liposomes is examined by using liposomes prepared with egg phosphatidylcholine or dipalmitoyl phosphatidylcholine and by varying the surface charge by addition of dicetyl phosphate. Light-scattering and osmotic behaviour studies showed that the stability of liposomes containing dicarboxylic phosphatidylcholine is influenced by the charge and the fatty acid saturation of the liposomes. Increasing the glutaryl phosphatidylcholine-to-phosphatidylcholine molar ratio in liposomes caused the formation of mixed glutaryl phosphatidylcholine/phosphatidylcholine micelles. The sensitivity of the lipid bilayers towards glutaryl phosphatidylcholine action increases with the fatty acid saturation of liposomes. Dipalmitoyl phosphatidylcholine liposomes are most sensitive to the dicarboxylic phosphatidylcholine effect. Dicetyl phosphate addition enhances the solubilization of liposomes prepared from saturated phospholipids. The effect of increasing concentrations of glutaryl phosphatidylcholine on the gel-to-liquid crystal thermal transition of dipalmitoyl phosphatidylcholine was observed. Glutaryl phosphatidylcholine modifies the thermal phase transition of the constituents of the liposome. The presence of dicetyl phosphate in liposomes affects the phase transition temperature of these liposomes. It is suggested that the formation of the mixed micelles is responsible for the phase transition modifications. These data show that the solubilization of liposomes by dicarboxylic phosphatidylcholines depends on the fatty acid composition of phosphatidylcholine and on the presence of dicetyl phosphate.

Liposomes↗

PubMed1979

Antagonism between high pressure and anesthetics in the thermal phase-transition of dipalmitoyl phosphatidylcholine bilayer.

The antagonizing action of hydrostatic pressure against anesthesia is well known. The present study was undertaken to quantitate the effects of hydrostatic pressure and anesthetics upon the phase-transition temperature of dipalmitoyl phosphatidylcholine vesicles. The drugs used to anesthetize the phospholipid vesicles included an inhalation anesthetic, halothane, a dissociable local anesthetic, lidocaine and an undissociable local anesthetic, benzyl alcohol. All anesthetics decreased the phase-transition temperature dose-dependently. In the case of lidocaine, the depression was pH dependent and only uncharged molecules were effective. The application of hydrostatic pressure increased the phase-transition temperature both in the presence and the absence of anesthetics. The temperature-pressure relationship was linear over the entire pressure range studied up to 340 bars. Through the use of Clapeyron-Clausius equation, the volume change accompanying the phase-transition of the membrane was calculated to be 27.0 cm3/mol. Although the anesthetics decreased the phase-transition temperature, the molar volume change accompanying the phase-transition was not altered. The anesthetics displaced the temperature-pressure lines parallel to each other. The mole fraction of the anesthetics in the liquid crystalline membrane, calculated from the van't Hoff equation, was independent of pressure. This implies that pressure does not displace the anesthetics from the liquid membrane, and the partition of these agents remains constant. The volume change of the anesthetized phospholipid membranes is entirely dependent upon the phase-transition and not on the space occupied by the anesthetics.

Anesthetics↗

PubMed1979

Studies on human finger tapping neural networks by phase transition curves.

The human finger tapping was studied psychologically by the phase transition curves. We assumed that some oscillatory neural network controls the tapping. One of our future works on the human finger tapping is to devise a method to change the magnitude of perturbation continuously in phase resetting experiments of a constant tapping interval with a same kind of task. If this is achieved, we can obtain a phase transition surface (i.e. the new phase as a function of the old phase and the magnitude of perturbation). From the shape of a phase transition surface, the intrinsic properties of the oscillatory network which controls the tapping can be studied (Kawato et al., 1978).

Conditioning, Psychological↗

PubMed1986

Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine. Effect on gel-to-liquid-crystalline phase transition of lipid bilayer.

The gel-to-liquid-crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was observed in the presence of various types of surfactants; sodium alkylsulfates, alkyltrimethylammonium bromides, alkanoyl-N-methylglucamides, and hexaethyleneglycol mono n-dodecyl ether. The phase transition was monitored by a change in scattered light intensity of the lipid suspension. For all the surfactants examined, the phase transition temperature was depressed linearly with the surfactant concentration in the measured concentration range, from which the partition coefficient, K, of the surfactant between bulk solution and lipid membrane was estimated. Except alkyltrimethylammonium bromides, log K and log CMC showed a linear relationship, which indicates that the driving force to transfer the surfactant from bulk solution to lipid membrane is a hydrophobic interaction. The addition of surfactants increased the transition width. The extent of widening the transition width was in the order of sodium alkylsulfate greater than alkyltrimethylammonium bromides greater than hexaethyleneglycol mono n-dodecyl ether; in the case of alkanoyl-N-methylglucamides, the transition width was not affected by the addition. These effects on the transition width was interpreted qualitatively in terms of the cooperativity of the transition.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1983

Order-disorder phase transition and lipid dynamics in rabbit small intestinal brush border membranes. Effect of proteins.

The total lipids extracted from brush border membranes form smectic lamellar phases when dispersed in water. 31P broad-band nuclear magnetic resonance (NMR) shows that between body temperature (37 degrees C) and freezing of the solvent, the extracted lipids form bilayers with the lipid molecules undergoing fast anisotropic motion. This is also true for the lipids present in the brush border membrane. The electron spin resonance (ESR) results obtained with various hydrophobic spin probes incorporated in either brush border vesicle membranes or their extracted lipids are consistent with this interpretation. By use of a variety of chemically different spin-labels, the temperature dependence of brush border membranes and their extracted lipids was probed. The temperature dependence of various ESR spectral parameters shows discontinuities that, by comparison with differential scanning calorimetry, are assigned to a lipid thermotropic phase transition. Differential scanning calorimetry shows that the lipid in brush border membranes undergoes a broad, reversible phase transition of low enthalpy between 10 and 30 degrees C, with a peak temperature of about 25 degrees C. Hence, the brush border membrane of rabbit small intestine functions in the liquid-crystalline state, well above the peak temperature and also above the upper limit of the lipid phase transition. Therefore, in itself, the thermotropic lipid phase transition is unlikely to play a physiological role. The low enthalpy of the lipid phase transition, indicative of a lack of cooperativity, is primarily attributed to the relatively high cholesterol content and to heterogeneity in the lipid composition of this membrane [Hauser, H., Howell, K., Dawson, R. M. C., & Bowyer, D. E. (1980) Biochim. Biophys. Acta 602, 567-577].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗