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PubMed1985

Advantages and limitations of 1-palmitoyl-2-[[2-[4- (6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl]carbonyl]-3- sn-phosphatidylcholine as a fluorescent membrane probe.

We have investigated the behavior of 1-palmitoyl-2-[[2-[4- (6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl]carbonyl]-3-sn -phosphatidylcholine (DPHpPC) in synthetic, multilamellar phosphatidylcholine vesicles. This fluorescent phospholipid has photophysical properties similar to its parent fluorophore, diphenylhexatriene (DPH). DPHpPC preferentially partitioned into fluid phase lipid (Kf/s = 3.3) and reported a lower phase transition temperature as detected by fluorescence anisotropy than that observed by differential scanning calorimetry. Calorimetric measurements of the bilayer phase transition in samples having different phospholipid to probe ratios demonstrated very slight changes in membrane phase transition temperature (0.1-0.2 degree C) and showed no measurable change in transition width. Nonetheless, measurements of probe fluorescence properties suggested that DPHpPC disrupts its local environment in the membrane and may even induce perturbed probe-rich local domains below the phospholipid phase transition. Temperature profiles of steady-state fluorescence anisotropy, limiting anisotropy, differential tangent, and rotational rate were similar to those of DPH below the main lipid phase transition but indicated more restricted rotational motion above the lipid phase transition temperature. As for DPH, the fluorescence decay of DPHpPC could be described by either a single or double exponential both above and below the DPPC phase transition. The choice seemed dependent on the treatment of the sample. The intensity-weighted average lifetime of DPHpPC was roughly 1.5 ns shorter than that of DPH. In summary, the measured properties of DPHpPC and its lipid-like structure make it a powerful probe of membrane structure and dynamics.

Fluorescence Polarization↗
PubMed1986

Studies on the phase transitions of lysoderivatives of ethanolamine glycerophospholipids from human brain.

The phase transition temperature of 1,2-distearoylglycerophosphocholine is reduced in presence of equimolar amounts of 1-O-(1'-alkenyl)-glycerophosphoethanolamine (ethanolamine lysoplasmalogen) from 53.3 degrees C-54.1 degrees C to 44.0 degrees C-44.9 degrees C at different pH (4.0; 7.2; 9.0; 10.5). 1-Acyl-glycerophosphoethanolamine leads to a smaller reduction of the 1,2-distearoyl-glycerophosphocholine transition temperature: 45.0 degrees C-46.2 degrees C at the same pH-values. 1-Alkyl-glycerophosphoethanolamine (hydrogenated ethanolamine lysoplasmalogen) possesses a transition temperature, which is 3.3 degrees C-4.9 degrees C higher than the hydrogenated 1-acyl-glycerophosphoethanolamine at each pH investigated. At pH 9.0 and, more pronounced, at pH 10.5 we find a reduction of the transition temperature for both these substances, whereas their transition temperature is nearly unchanged at pH 4.0 and 7.2. Our results clearly show that the ether-bonding in the lysoderivative of plasmalogen is responsible for the closer packing compared to the 1-acyl-glycerophosphoethanolamine.

Brain Chemistry↗
PubMed1987

Calcium-sensitive thermal transitions and domain structure of human complement subcomponent C1r.

Fluorescent probes and other methods have been used to investigate the thermal stability of activated C1r and functionally intact fragments isolated from tryptic digests of the protein. This enzyme exhibits two irreversible transitions that differ with respect to their sensitivity to metal ions. The high-temperature transition occurs with a midpoint near 53 degrees C in 0.02 M tris(hydroxymethyl)aminomethane buffer and 0.15 M NaCl, pH 7.4. It is relatively insensitive to Ca2+ and ionic strength and is accompanied by a loss of catalytic activity. The low-temperature transition is most easily observed in the presence of ethylenediaminetetraacetic acid and is completely abolished by 100 microM Ca2+. Its midpoint varies between 26 degrees C at low ionic strength and 40 degrees C in the presence of 0.5 M NaCl. The low-temperature transition results in extensive polymerization of the protein without loss of the esterolytic activity or the ability to react with C1 inhibitor; however, the ability to reconstitute hemolytically active C1 or even bind to C1s in the presence of Ca2+ is destroyed. A highly purified N-terminal fragment generated by tryptic digestion of C1r in the presence of Ca2+ retained its ability to interact with C1s, disrupting the formation of C1s dimers in the presence of Ca2+. In the absence of Ca2+, this fragment displays only a low-temperature transition that is very similar to the one observed with the whole protein and that destroys its ability to bind to C1s. Addition of Ca2+ stabilizes this fragment, shifting the midpoint of its melting transition upward by more than 20 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Anilino Naphthalenesulfonates↗
PubMedDate not supplied

Temperature-dependent associating property of liposomes modified with a thermosensitive polymer.

Novel temperature-sensitive liposomes having surface properties that can be controlled by temperature were designed as liposomes coated with poly(N-isopropylacrylamide), which exhibits a hydrated coil to dehydrated globule transition at ca. 32 degrees C. To obtain the polymer with anchoring groups to the liposome, a copolymer of N-isopropylacrylamide and octadecyl acrylate (99:1, mol/mol) was synthesized by radical copolymerization. The copolymer revealed the transition near 30 degrees C. Liposomes made from various phospholipids were prepared by sonication and coated with the copolymer. When dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine were used as liposome lipids, remarkable aggregation and fusion of the copolymer-modified liposomes took place between the transition temperature of the copolymer and the gel-liquid-crystalline transition temperature (Tc) of the lipid membranes. However, above the Tc, association between the liposomes was much less significant, although the copolymer is still hydrophobic. In the case of the copolymer-modified dilauroylphosphatidylcholine liposome, the membrane of which takes on a liquid-crystalline state under the experimental conditions, association between the liposomes also hardly occurred even when the copolymer became hydrophobic. On the other hand, below the transition temperature of the copolymer, the copolymer-modified liposomes were very stable and aggregation of the liposomes was not observed, irrespective of membrane lipid. Results obtained in this study demonstrate that the copolymer chains fixed on the surface of the liposome with a solid membrane promote aggregation and fusion of the liposomes by hydrophobic interactions between the copolymer chains and/or between the copolymer chains and the liposome membranes above the transition temperature of the copolymer.

Acrylamides↗
PubMed1995

13C-NMR off-resonance rotating frame spin-lattice relaxation studies of bovine lens gamma-crystallin self association: effect of 'macromolecular crowding'.

The NMR technique of 13C off-resonance rotating frame spin-lattice relaxation, which provides an accurate assessment of the effective rotational correlation time (tau 0, eff) for macromolecular rotational diffusion, was applied to the study of gamma-crystallin association as a function of protein concentration and temperature. Values of the effective rotational correlation time for gamma-crystallin rotational diffusion were obtained at moderate to high protein concentrations (80-350 mg/ml) and at temperatures above, and below, the cold cataract phase transition temperature. With increasing concentration gamma-crystallin was observed to increasingly associate as reflected by larger values of tau 0, eff Decreasing temperature in the range of 35 to 22 degrees C was found to result in no change in the temperature corrected value of tau 0, eff at a gamma-crystallin concentration of 80 mg/ml, whereas at temperatures of 18 degrees C or below, this parameter was approx. twofold larger, suggesting the occurrence of a well defined phase transition, which correlated well with the cold cataract phase transition temperature. At higher protein concentrations, by contrast, tau 0, eff (temperature corrected) was found to increase by approx. 1.6- to 2-times in the temperature interval 35 degrees C to 22 degrees C, a result consistent with the dependence of the cold cataract phase transition temperature on gamma-crystallin concentration. Analysis of intensity ratio dispersion curves, using an assumed model of isodesmic association, permitted the estimation of the association constant characterizing the aggregation under particular conditions of concentration and temperature. The significant increase in the value of the association constant with moderate increases in protein concentration was rationalized by invoking the effect of 'macromolecular crowding'. The results obtained in this study suggest that in the intact lens, where high protein concentrations prevail, gamma-crystallin is unlikely to be found in the monomeric state, but more likely, as a significantly aggregated species, representing a broad molecular weight distribution.

Animals↗
PubMed2002

In situ epitaxial MgB2 thin films for superconducting electronics.

The newly discovered 39-K superconductor MgB2 holds great promise for superconducting electronics. Like the conventional superconductor Nb, MgB2 is a phonon-mediated superconductor, with a relatively long coherence length. These properties make the prospect of fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favourable for MgB2 than for high-temperature superconductors. The higher transition temperature and larger energy gap of MgB2 promise higher operating temperatures and potentially higher speeds than Nb-based integrated circuits. However, success in MgB2 Josephson junctions has been limited because of the lack of an adequate thin-film technology. Because a superconducting integrated circuit uses a multilayer of superconducting, insulating and resistive films, an in situ process in which MgB2 is formed directly on the substrate is desirable. Here we show that this can be achieved by hybrid physical-chemical vapour deposition. The epitaxially grown MgB2 films show a high transition temperature and low resistivity, comparable to the best bulk samples, and their surfaces are smooth. This advance removes a major barrier for superconducting electronics using MgB2.

Journal Article↗
PubMed1987

Lipid intermolecular hydrogen bonding: influence on structural organization and membrane function.

The great variety of different lipids in membranes, with modifications to the hydrocarbon chains, polar groups and backbone structure suggests that many of these lipids may have unique roles in membrane structure and function. Acidic groups on lipids are clearly important, since they allow interaction with basic groups on proteins and with divalent cations. Another important property of certain lipids is their ability to interact intermolecularly with other lipids via hydrogen bonds. This interaction occurs through acidic and basic moieties in the polar head groups of phospholipids, and the amide moiety and hydroxyl groups on the acyl chain, sphingosine base and sugar groups of sphingo- and glycolipids. The putative ability of different classes of lipids to interact by intermolecular hydrogen bonding, the molecular groups which may participate and the effect of these interactions on some of their physical properties are summarized in Table IX. It is frequently questioned whether intermolecular hydrogen bonding could occur between lipids in the presence of water. Correlations of their properties with their molecular structures, however, suggest that it can. Participation in intermolecular hydrogen bonding increases the lipid phase transition temperature by approx. 8-16 Cdeg relative to the electrostatically shielded state and by 20-30 Cdeg relative to the repulsively charged state, while having variable effects on the enthalpy. It increases the packing density in monolayers, possibly also in the liquid-crystalline phase in bilayers, and decreases the lipid hydration. These effects can probably be accounted for by transient, fluctuating hydrogen bonds involving only a small percentage of the lipid at any one time. Thus, rotational and lateral diffusion of the lipids may take place but at a slower rate, and the lateral expansion is limited. Intermolecular hydrogen bonding between lipids in bilayers may be significantly stabilized, despite the presence of water, by the fact that the lipids are already intermolecularly associated as a result of the hydrophobic effect and the Van der Waals' interactions between their chains. The tendency of certain lipids to self-associate, their asymmetric distribution in SUVs, their preferential association with cholesterol in non-cocrystallizing mixtures, their temperature-induced transitions to the hexagonal phase and their inhibitory effect on penetration of hydrophobic residues of proteins partway into the bilayer can all be explained by their participation in intermolecular hydrogen bonding interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Membrane↗
PubMed1981

Temperature dependence of the concentration kinetics of absorption of phosphate and potassium in corn roots.

The effect of temperature on respiration and kinetics of H(2)PO(4) (-) and K(+) uptake in corn roots was determined in the range of 2 to 42 C. The response of uptake to temperature, determined from Q(10) and activation energy (Ea) data, for the anion and the cation differ significantly, especially in the range of uptake mechanism (Mech.) I. At 2.5 micromolar the Ea for K(+) uptake below the 13 C transition is 29.3 kilocalories per mole. As the K(+) concentration is increased, Ea declines and at 0.25 millimolar is 21.6 kilocalories per mole. Accompanying this change in Ea is a shifting of the apparent transition temperature from 13 to 17 C. Above the temperature transition the Ea's for K(+) uptake in the Mech. I range are quite low (3.0) and this value is unchanged by increases of K(+) concentration to 0.25 millimolar. In the range of Mech. II above 1 millimolar K(+) the temperature transitions are not seen and plots become linear. The Ea's show an increasing trend from 4.7 at 1 millimolar to 6.1 at 50 millimolar. The uptake of H(2)PO(4) (-) is much more temperature sensitive having a constant Ea at concentrations in the Mech. I range below the 13 C temperature transition. The Arrhenius plots reveal a second transition at 22 C and the Ea for this segment is 21.0. Above the second transition the Ea remains high (10.0) and is constant in the range of Mech. I. In the range of Mech. II there is a concentration dependent decline in Ea for H(2)PO(4) (-) uptake (22.7 at 1.0 millimolar to 1.0 at 50 millimolar). There is no definable low temperature transition at these concentrations. Ion uptake is found to be much more sensitive to low temperature than respiration in this chill-sensitive species. The data suggest that the low temperature reduction of ion transport is more closely related to restriction of function of active transport systems than to either respiration or membrane permeability.

Journal Article↗
PubMed1995

Role of phospholipids containing docosahexaenoyl chains in modulating the activity of protein kinase C.

It is known that the phospholipids of the brain cells of fish are altered during cold adaptation. In particular, the 1-monounsaturated 2-polyunsaturated phosphatidylethanolamines (PEs) increase 2- to 3-fold upon adaptation to cold. One of the most striking changes is in the 18:1/22:6 species of PE. We determined how this lipid affected the bilayer-to-hexagonal-phase transition temperature of 16:1/16:1 PE. We found that it was more effective in lowering this transition temperature than were other, less unsaturated, PE species. In addition, it was not simply the presence of the 18:1/22:6 acyl chains which caused this effect, since the 18:1/22:6 species of phosphatidylcholine had the opposite effect on this transition temperature. Zwitterionic substances that lower the bilayer-to-hexagonal-phase transition temperature often cause an increase in the activity of protein kinase C (PKC). Indeed, the 18:1/22:6 PE caused an increase in the rate of histone phosphorylation by PKC which was greater than that caused by other, less unsaturated, PEs. The 18:1/22:6 phosphatidylcholine had no effect on this enzyme. The stimulation of the activity of PKC by the 18:1/22:6 PE is a consequence of this lipid's increasing the partitioning of PKC to the membrane.

Calorimetry, Differential Scanning↗
PubMed1995

Thermodynamics of denaturation of alpha-chymotrypsinogen A in aqueous urea and alkylurea solutions.

The effects of pH, urea, and alkylureas on the thermal stability of alpha-chymotrypsinogen A (alpha-ctg A) have been investigated by differential scanning calorimetry (DSC) and UV spectroscopy. Heat capacity changes and enthalpies of transition of alpha-ctg A in the presence of urea and alkylureas were measured at the transition temperature. Using these data, the corresponding Gibbs free energies, enthalpies, and entropies of denaturation at 25 degrees C were calculated. Comparison of these values shows that at 25 degrees C denaturation with urea is characterized by a significantly smaller enthalpy and entropy of denaturation. At all denaturant concentrations the enthalpy term slightly dominates the entropy term in the Gibbs free energy function. The most obvious effect of alkylureas was lowering of the temperature of transition, which was increasing with alkylurea concentration and the size of alkyl chain. Destabilization of the folded protein in the presence of alkylureas appears to be primarily the result of the weakening of hydrophobic interactions due to diminished solvent ordering around the protein-molecules. At pH lower than 2.0, alpha-ctg A still exists in a very stable form, probably the acid-denatured from (A-form).

Calorimetry, Differential Scanning↗
PubMed1976

Experimental evidence for high-temperature organic fractional superconduction in cholates.

Experimental data are presented indicating that six organic compounds (homologous cholates) possess properties associated with high-temperature superconductivity. From magnetic and electrical measurements it is deduced that behavior resembling superconductivity occurs below characteristic transition temperatures in small domains included in the insulating bulk of the sample material, which is therefore designated a fractional o Type III superconductor. The six cholates exhibit this superconductivity below transition temperatures ranging from approximately 7.5 degrees K for sodium dioxycholate to 277 degrees K for sodium cholanate. It has been further established that the diamagnetic shifts with temperature cannot be attributed to ferrielectric, ferroelectric, or capacitive effects. Below the transition temperatures the cholates behave like perfect diamagnets, susceptible to forceful repulsion by a moderate magnetic field. Observed in a sensitive susceptometer, magnetic flux trapped in the material gave rise to a 3% remnant magnetic moment. Studied in particular detail were sodium cholate, sodium deoxycholate, and lithocholic acid, which showed transition temperatures of 30 degrees K, 60 degrees K, and 130 degrees K respectively. The hydrophobic property of the closed four-ring structure (R-group) common to the cholates, along with the hydrophilic property of the carboxylate group (S-group), are responsible for domain formation. Because of those properties, clustering of the S-groups occurs when traces of water are introduced into the material. When followed by slow desiccation, the clusters form the micelles constituting the superconducting domains.

Cholic Acids↗
PubMed1982

Pressure dependence of pyrene excimer fluorescence in human erythrocyte membranes.

The intensity of pyrene excimer fluorescence in human erythrocyte membranes and in sonicated dispersions of the membrane lipid (liposomes) was examined as a function of pressure (1-2080 bar) and temperature (5-40 degrees C). Higher pressure or lower temperature decreased the excimer/monomer intensity ratios. A thermotropic transition was detected in both membranes and liposomes by plots of the logarithm of the excimer/monomer intensity ratio versus 1/K. The transition temperature of the membranes was 19-21 degrees C at 1 bar and 28-31 degrees C at 450 bar, a shift with pressure of approx. 20-22 K per kbar. Corresponding transition temperatures of the liposomes were 21 degrees C at 1 bar and 33 degrees C at 450 bar, a shift of approx. 27 K per kbar. The observed pressure dependence of the thermotropic transition temperature is similar to that reported for phospholipid bilayers and greatly exceeds that of protein conformation changes. In concert with the liposome studies the results provide direct evidence for a lipid transition in the erythrocyte membrane.

Erythrocyte Membrane↗
PubMed2006

Supported absorption of CO2 by tetrabutylphosphonium amino acid ionic liquids.

A new type of "task specific ionic liquid", tetrabutylphosphonium amino acid [P(C4)4][AA], was synthesized by the reaction of tetrabutylphosphonium hydroxide [P(C4)4][OH] with amino acids, including glycine, L-alanine, L-beta-alanine, L-serine, and L-lysine. The liquids produced were characterized by NMR, IR spectroscopies, and elemental analysis, and their thermal decomposition temperature, glass transition temperature, electrical conductivity, density, and viscosity were recorded in detail. The [P(C4)4][AA] supported on porous silica gel effected fast and reversible CO2 absorption when compared with bubbling CO2 into the bulk of the ionic liquid. No changes in absorption capacity and kinetics were found after four cycles of absorption/desorption. The CO2 absorption capacity at equilibrium was 50 mol % of the ionic liquids. In the presence of water (1 wt %), the ionic liquids could absorb equimolar amounts of CO2. The CO2 absorption mechanisms of the ionic liquids with and without water were different.

Journal Article↗
PubMed2001

Study of the Second Order Transitions and Acid-Base Properties of Polymers Adsorbed on Oxides by Using Inverse Gas Chromatography at Infinite Dilution.

In Part I, we gave the details concerning inverse gas chromatography (IGC) at infinite dilution and the methods and models that will be used to characterize solid substrates. This technique proved to be an excellent technique to determine not only the glass transitions, but also beta-transition and liquid-liquid transitions of polymers adsorbed on solid substrates. In this second part, we used the IGC technique to determine the second order transitions of the systems' polymethyl methacrylate (PMMA)/SiO(2) and PMMA/Al(2)O(3), at various covered surface fractions and for various tacticities of the polymer. The maxima of the dispersive component of the surface energy gamma(s)(d) of our two systems, obtained by IGC at infinite dilution, indicated clearly the presence of transition temperatures (glass or local transitions). In general, we observed with PMMA three principal maxima that reflect the changes in motions leading to reorganization and rearrangement of the various groups or chain segments of the polymer. The change in the retention mechanism of the probes at the transition temperatures is attributed to an increased molecular mobility of the polymer segments, allowing for the penetration of the probes into the polymer layer. The study of the chemical physical properties of PMMA/SiO(2) and PMMA/Al(2)O(3) revealed an important difference in the acidic and basic behavior, in Lewis terms, of oxide covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the acidic basic character of PMMA adsorbed on oxides. Copyright 2001 Academic Press.

Journal Article↗
PubMed1979

HCO3-/Cl- exchange across the human erythrocyte membrane: effects of pH and temperature.

Changes in extracellular pH (PH0) in red cell suspensions were monitored in a stopped-flow rapid reaction apparatus under conditions where dpH0/dt was determined by the rate of HCO3-/Cl- exchange across the membrane. Experiments were performed at 5 degrees C less than T less than 40 degrees C using either untreated cells or cells exposed to 0.11 mM SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid). Although SITS exposure reduced the rate of exchange by 90%, both untreated and SITS-treated cells are similarly affected by changes in pH0 and temperature. The rate of HCO3-/Cl- exchange exhibits a minimum at about pH0 5 and a maximum at about pH0 7.4 at all temperatures. A transition temperature of 17 degrees C was observed in the Arrhenius relationship for all pH0. The activation energies (Ea) in kcal/mol are 19.6 below and 11.7 above 17 degrees C for 5 less than pH0 less than 8. These findings, similar to those reported for Cl- self-exchange, suggest that: (i) a change in the rate-limiting step for HCO3-/Cl- exchange occurs at 17 degrees C, possibly due to an altered interaction between the transport pathway and membrane lipids; (ii) the carrier system can be titrated by either H+ or SITS from the outside of the membrane, but the untitrated sites continue to transport normally; (iii) the pH0 dependence of the rate of exchange is consistent with the titratable carrier having its most alkaline pK in the range expected for amino groups; and (iv) below pH0 5, the nature of the exchange is markedly altered.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed2005

Degradation of medium-chain-length polyhydroxyalkanoates in tropical forest and mangrove soils.

Bacterial polyhydroxyalkanoates (PHAs) are perceived to be a suitable alternative to petrochemical plastics because they have similar material properties, are environmentally degradable, and are produced from renewable resources. In this study, the in situ degradation of medium-chain-length PHA (PHAMCL) films in tropical forest and mangrove soils was assessed. The PHAMCL was produced by Pseudomonas putida PGA1 using saponified palm kernel oil (SPKO) as the carbon source. After 112 d of burial, there was 16.7% reduction in gross weight of the films buried in acidic forest soil (FS), 3.0% in the ones buried in alkaline forest soil by the side of a stream (FSst) and 4.5% in those buried in mangrove soil (MS). There was a slight decrease in molecular weight for the films buried in FS but not for the films buried in FSst and in MS. However, no changes were observed for the melting temperature, glass transition temperature, monomer compositions, structure, and functional group analyses of the films from any of the burial sites during the test period. This means that the integral properties of the films were maintained during that period and degradation was by surface erosion. Scanning electron microscopy of the films from the three sites revealed holes on the film surfaces which could be attributed to attack by microorganisms and bigger organisms such as detritivores. For comparison purposes, films of polyhydroxybutyrate (PHB), a short-chain-length PHA, and polyethylene (PE) were buried together with the PHAMCL films in all three sites. The PHB films disintegrated completely in MS and lost 73.5% of their initial weight in FSst, but only 4.6% in FS suggesting that water movement played a major role in breaking up the brittle PHB films. The PE films did not register any weight loss in any of the test sites.

Biodegradation, Environmental↗
PubMed1982

Effect of phosphatidylinositol replacement by diacylglycerol on various physical properties of artificial membranes with respect to the role of phosphatidylinositol response.

In an attempt to gain insight into the physiological role of phosphatidylinositol turnover enhanced by extracellular stimuli, the physical properties of artificial membranes (egg yolk phosphatidylcholine/bovine brain phosphatidylserine) containing phosphatidylinositol or diacylglycerol were studied by ESR using spin probes and freeze-fracture electron microscopy. Diacylglycerol lost both the ability to form lipid bilayer structures and its susceptibility to calcium ions. Yeast phosphatidylinositol included in dipalmitoylphosphatidylcholine liposomes lowered the phase transition temperature of dipalmitoylphosphatidylcholine and expanded the temperature range of phase transition. However, diacylglycerol at the same concentration did not undergo the effects caused by phosphatidylinositol but the phase transition temperature was slightly raised. Phase separation of phosphatidylserine induced by calcium ions was enhanced when the phosphatidylinositol was replaced by diacylglycerol in phosphatidylcholine/phosphatidylserine/phosphatidylinositol (3:5:2, by molar ratio) mixtures. The mobility of phosphatidylcholine spin probe was decreased in phosphatidylcholine/phosphatidylserine/diacylglycerol (3:5:2, by molar ratio) liposomes compared with phosphatidylcholine/phosphatidylserine/phosphatidylinositol (3:5:2, by molar ratio) liposomes. An additional component from protonated stearic acid spin probes was observed in phosphatidylcholine/phosphatidylinositol (8:2, by molar ratio) liposomes at 40 degrees C, whereas the component was not seen in phosphatidylcholine/diacylglycerol (8:2, by molar ratio) liposomes. This may indicate the alteration of surface charge induced by the replacement of phosphatidylinositol by diacylglycerol. Indeed, in the presence of 1 mM Ca2+, the additional component was removed by an electrostatic interaction between Ca2+ and phosphatidylinositol molecules in phosphatidylcholine/phosphatidylinositol liposomes at 40 degrees C. These results support the hypothesis that the enhanced turnover of phosphatidylinositol may play a triggering role for various cellular responses to exogenous stimuli by altering membrane physical states.

Diglycerides↗
PubMed1993

Effect of N-acylethanolamines with different acyl-chains on DPPC multilamellar liposomes.

The influence of N-acylethanolamines with different acyl-chains on the physico-chemical state of neutral phospholipids was investigated using dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes. The thermal dependence of steady state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and its charged derivative 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) was recorded. The N-acylethanolamines modified the DPPC phase transition temperature and broadened the transition temperature range in different ways depending on the N-acylethanolamines acyl chain characteristics. Our data suggest that the N-acylethanolamine acyl chain length and unsaturation play an important role in the interaction of these compounds with model membranes. The results show that long-chain-N-acylethanolamines interact largely with DPPC model membranes while a similar effect is not observed for the short ones.

1,2-Dipalmitoylphosphatidylcholine↗