Fourier-transform infrared spectroscopy studies of lipid/protein interaction in pulmonary surfactant

The thermotropic behavior of intact bovine lung surfactant and its hydrophobic extract has been monitored via the temperature dependence of the 2850 cm-1 phospholipid acyl chain CH2 symmetric stretching frequencies in the IR spectrum. A broad, reversible, melting event was noted from about 15 to 40 degrees C in both the lipid extract and the native surfactant. Slight protein-induced disordering of the lipid acyl chains was evident. The melting event was confirmed by differential scanning calorimetry. The major surfactant protein, a 30-36-kDa class of glycoprotein (SP-A), has been isolated from bovine lung lavage and purified by affinity chromatography. SP-A was reconstituted into a binary lipid mixture of acyl chain perdeuterated dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol (DPPC-d62/DPPG, 85:15 w/w), a ratio which approximates that in surfactant. Use of DPPC-d62 permitted the FT-IR determination of the effect of protein on the thermotropic behavior of individual phospholipids in the binary mixture. High levels of SP-A induced an ordering of the phospholipids, as shown by an increase in the transition temperature of DPPC-d62 compared to the lipid model. In contrast, a mixture of the other surfactant proteins induced a progressive disordering of the phospholipids and disruption of the cooperativity of the melting event. Transition widths of about 3 degrees, 9 degrees, and 27 degrees were noted for protein:lipid ratios of 0, 1:1, and 2:1 (w/w), respectively. Possible roles for the various proteins in surfactant function are discussed in light of these data.     

Fourier transform infrared study on the thermotropic behaviour of fully hydrated 1-palmitoyl-2-[10-(pyren-1-y) decanoyl]-sn-glycero-3-phosphatidylcholine

Fourier transform infrared (FTIR) spectroscopy was used to study the thermotropic behaviour of fully hydrated 1-palmitoyl-2-[10-(pyren-1-yl)-decanoyl]-sn-glycero-3-phosphatidyl choline (PPDPC) in the temperature range of 3-30 degrees C. Several changes in the spectral features of PPDPC were observed. Major alterations analogous to the gel-to-liquid crystalline phase transition of saturated phosphatidylcholines were evident at approximately 16 degrees C in both the wavenumbers and the halfbandwidths of five different vibrational modes of PPDPC, viz. asymmetric and symmetric CH2 stretching, C = O stretching, and CH2 bending. Also the pyrene ring deformation mode changed at this temperature. Using Fourier self-deconvolution technique we resolved the carbonyl stretching mode into two bands at approx. 1741 and 1726 cm-1. These bands are due to conformational differences in the ester linkages of the two acyl chains, and are further assigned on the basis of literature data to the sn-1 and sn-2 carbonyl groups, respectively. The ratio of the relative intensities of these two bands is shown to depend on the phase state of the phospholipid.     

Calorimetric and infrared spectroscopic studies of the interaction of alpha-tocopherol and alpha-tocopheryl acetate with phospholipid vesicles

The location of alpha-tocopherol and alpha-tocopheryl acetate in the membrane has been a subject of considerable interest, not only because of their relevant physiological function, but also for understanding their interaction with the phospholipids. We have examined this question by using reconstituted systems including dipalmitoyl-glycerophosphocholine multibilayer vesicles to which alpha-tocopherol and alpha-tocopheryl acetate were incorporated. Differential scanning microcalorimetry measurements showed that both compounds were capable of modifying the thermotropic properties of the pure phospholipid, so that the pretransition disappears at low concentrations of these terpenoid molecules. The enthalpy corresponding to the main transition decreases as the concentration of alpha-tocopherol increases and the transition peak is progressively shifted to lower temperatures. alpha-Tocopheryl acetate gave the same type of effect but less marked than in the case of alpha-tocopherol. Fourier-transform infrared spectroscopic measurements were also made on these systems and the temperature dependence of the infrared spectra was studied. A comparison of the spectroscopic data showed that, in agreement with the calorimetric results, alpha-tocopherol remarkably perturbs the thermotropic phase transition of dipalmitoylglycerophosphocholine. It was concluded from a study of the CH2 stretching bands that alpha-tocopherol induced changes in frequency and in bandwidth parameters. However, the changes in frequency and bandwidth with respect to temperature are not concerted; this is a consequence of the existence of more than one phase in the presence of alpha-tocopherol. From the study of the CH2 scissoring band, it was concluded that alpha-tocopherol disrupts the acyl chain packing present in pure dipalmitoylglycerophosphocholine below the onset temperature of the gel-to-liquid-crystal transition. The effect of alpha-tocopheryl acetate is of a similar type to that of alpha-tocopherol but weaker with respect to these stretching and scissoring CH2 bands. Spectral changes were also found in the C = O stretching mode of the phospholipid in the presence of alpha-tocopherol and these changes were attributed to perturbations in the C1-C2 bonds of sn-2-acyl chains of the phospholipid. These effects were much weaker in the case of alpha-tocopheryl acetate; it is suggested that this may be due to a specific interaction between alpha-tocopherol and the polar region of the phospholipid. This interaction seems to be absent in the systems containing alpha-tocopheryl acetate.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fourier transform infrared study of fully hydrated dimyristoylphosphatidylglycerol. Effects of Na+ on the sn-1' and sn-3' headgroup stereoisomers

Molecular packing and the thermotropic phase behavior of fully hydrated ammonium salts of 1,2-dimyristoyl-sn-glycero-3-phosphatidyl-sn-1'-glycerol (1'-DMPG) and the corresponding 3' stereoisomer (3'-DMPG) as well as the effects of 300 mM NaCl on these lipids were studied by Fourier transform infrared (FTIR) spectroscopy. The ammonium salts of both stereoisomer show similar thermotropic phase behavior and have an order-disorder phase transition at approximately 21 degrees C. While complexing with Na+, however, an incubation of liposomes at +6 degrees C for 3 days results in significant structural differences between liposomes of 1'-DMPG and 3'-DMPG. In the presence of 300 mM NaCl the infrared spectra for 3'-DMPG reveal the appearance of a more solidified lipid nominated here as the highly crystalline phase with a transition into the liquid-crystalline state at a significantly higher temperature (approximately at 33 degrees C) than that for 1'-DMPG (approximately at 23 degrees C). Crystal field splitting resulting from interchain vibrational coupling is observed in the CH2 scissoring mode of the 3'-DMPG(Na+) complex in the highly crystalline phase (T less than 33 degrees C); i.e., the acyl chains are packed in a rigid orthorhombic- or monoclinic-like crystal lattice. At temperatures above the transition at 33 degrees C the acyl chains of 3'-DMPG(Na+) give rise to infrared spectra indicative of hexagonal packing. The latter type of hydrocarbon chain packing is also found for the ammonium salts of 1'-DMPG and 3'-DMPG without Na+ as well as for 1'-DMPG with Na+. In addition, the binding of Na+ to 3'-DMPG causes narrowing of the bands associated with the interfacial and polar headgroup regions of 3'-DMPG and thus reveals reduced motional freedom. This demonstrates that Na+ binds tightly to 3'-DMPG, leading to the immobilization of the entire phospholipid polar headgroup. Such effects by Na+ are not observed for 1'-DMPG.     

Calcium ion interactions with insoluble phospholipid monolayer films at the A/W interface. External reflection-absorption IR studies.

External reflection Fourier transform infrared (FT-IR) experiments are reported for insoluble monomolecular films of an equimolar mixture of 1,2-dipalmitoylphosphatidylcholine (DPPC) and 1,2-dipalmitoylphosphatidylserine (DPPS) at the A/W interface as a function of surface pressure and Ca2+ ion presence. The separate components showed a surface pressure-induced conformational ordering of the acyl chains. The conformational ordering occurred more cooperatively for the DPPS. Acyl chain perdeuteration of the DPPC permitted the observation of the response of the individual components in the binary mixture to changes in surface tension and to the presence of Ca2+. Plots of surface pressure versus CH2 or CD2 stretching frequencies were analyzed with a two-state model. At each surface pressure within the two-state region, the fraction of disordered form was the same for each lipid component, suggesting that they are well mixed on the surface. Calcium ion (5 mM in the subphase) produces almost no effect on the pressure-induced acyl chain ordering of the DPPC in a single component film, whereas the same levels of Ca2+ induce acyl chain ordering at all surface pressures in both components of the binary mixture. Thus, unlike the bulk phase mixture of DPPC/DPPS, the binary lipids in this mixed monolayer film appear to retain their miscibility in the presence of Ca2+. Finally, Ca(2+)-induced dehydration of the phosphate group was observed through characteristic frequency shifts in the asymmetric PO2- stretching mode.     

Effects of cholesterol on the interaction of Ca2(+)-ATPase with 1-palmitoyl-2-oleoylphosphatidylethanolamine. An FTIR study

Ca2(+)-ATPase from rabbit skeletal muscle has been isolated, purified, and reconstituted into vesicles containing binary mixtures of 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE)/cholesterol. Fourier transform infrared spectroscopy (FTIR) was used to investigate the effect of protein on the thermotropic behavior of POPE in these reconstituted ternary complexes. The CH2 symmetric stretching modes of the phospholipid acyl chains near 2850 cm-1 served as an index of the melting process. The thermotropic transition of the POPE component in a 103:12:1 (POPE/cholesterol/Ca2(+)-ATPase) complex was shifted to lower temperatures compared with a protein-free binary lipid mixture of the same relative proportions. When combined with differential scanning calorimetric (DSC) data for the binary (POPE/cholesterol) lipid systems, this observation suggests that Ca2(+)-ATPase preferentially sequesters 15-35 molecules of POPE from the lipid mixture and therefore excludes cholesterol from its immediate environment. Higher levels of cholesterol in ternary complexes progressively eliminate the cooperative POPE melting event.     

Effect of hydrophobic surfactant proteins SP-B and SP-C on binary phospholipid monolayers: II. Infrared external reflectance-absorption spectroscopy

In situ external reflection infrared spectroscopy at the air-water interface was used to study the influence on phospholipid structure of an endogenous mixture of the two hydrophobic surfactant proteins, SP-B and SP-C, which are thought to play pivotal roles in the adsorption and function of pulmonary surfactant. Mixtures studied were 1:1, 2:1, and 7:1 (mol:mol) DPPC-d(62):DPPG, and 7:1 DPPC-d(62):DOPG, alone and in the presence of 0.5-10 wt % mixed SP-B/C purified chromatographically from calf lung surfactant extract. Perdeuteration of DPPC produced a shift in vibrational frequencies so that it could be differentiated spectroscopically from the phosphoglycerol component in the surface monolayer. CH(2) antisymmetric and symmetric stretching bands ( approximately 2920 and 2852 cm(-1)) along with the analogous CD(2) stretching bands ( approximately 2194 and 2089 cm(-1)) were analyzed, and band heights and peak wavenumber positions were assessed as a function of monolayer surface pressure. Small, near-physiological contents of 1-2 wt % SP-B/C typically produced the maximum observed spectroscopic effects, which were abolished at high protein contents of 10 wt %. Analysis of CH(2) and CD(2) stretching bands and C-H/C-D band height ratios indicated that SP-B/C affected PC and PG lipids differently within the surface monolayer. SP-B/C had preferential interactions with DPPG in 1:1, 2:1, and 7:1 DPPC-d(62):DPPG films that increased its acyl chain order. SP-B/C also interacted specifically with DOPG in 7:1 DPPC-d(62):DOPG monolayers, but in this case an increase in CH(2) band heights and peak wavenumber positions indicated a further disordering of the already fluid DOPG acyl chains. CD(2) band height and peak wavenumber analysis indicated that SP-B/C had no significant effect on the structure of DPPC-d(62) chains in 7:1 films with DPPG or DOPG, and had only a slight tendency to increase the acyl chain order in 1:1 films of DPPC-d(62):DPPG. SP-B/C had no significant effect on DPPC-d(62) structure in films with DOPG. Infrared results also indicated that interactions involving SP-B/C and lipids led to exclusion of PC and PG lipids from the compressed interfacial monolayer, in agreement with our previous report on the phase morphology of lipid monolayers containing 1 wt % SP-B/C.     

Raman spectroscopy of nerve fibers. A study of membrane lipids under steady state conditions.

The molecular structures of different nerve fibers kept in good physiological conditions were studied by laser Raman spectroscopy. For myelinated nerves like the rat sciatic nerve, the Raman spectrum is dominated by bands due to the lipid component of the myelin sheath. The temperature dependence of these bands does not reveal any thermotropic phase transition between 0 and 40 degrees C. There is, however, with temperature, a linear increase in the intermolecular disorder that is accompanied by an increase in the number of gauche bonds of the phospholipid acyl chains. For unmyelinated nerves such as the lobster leg nerve, the C-H stretching region of the Raman spectrum is covered by bands arising from the protein component of the axoplasm. However, for the garfish olfactory nerve that has a high density of excitable membranes, phospholipid bands are observed and can be used as intrinsic structural probes of the excitable membranes. The relative intensity of these bands is also temperature dependent.     

Stages of the bilayer-micelle transition in the system phosphatidylcholine-C12E8 as studied by deuterium- and phosphorous-NMR, light scattering, and calorimetry.

The perturbation of phospholipid bilayer membranes by a nonionic detergent, octaethyleneglycol mono-n-dodecylether (C12E8), was investigated by 2H- and 31P-NMR, static and dynamic light scattering, and differential scanning calorimetry. Preequilibrated mixtures of the saturated phospholipids 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC), and 1,2-dilauroyl-sn-glycero-3-phosphorylcholine (DLPC) with the detergent were studied over a broad temperature range including the temperature of the main thermotropic phase transition of the pure phospholipids. Above this temperature, at a phospholipid/detergent molar ratio 2:1, the membranes were oriented in the magnetic field. Cooling of the mixtures below the thermotropic phase transition temperatures of the pure phospholipids led to micelle formation. In mixtures of DPPC and DMPC with C12E8, a narrow calorimetric signal at the onset temperature of the solubilization suggested that micelle formation was related to the disorder-order transition in the phospholipid acyl chains. The particle size changed from 150 nm to approximately 7 nm over the temperature range of the bilayer-micelle transition. The spontaneous orientation of the membranes at high temperatures enabled the direct determination of segmental order parameters from the deuterium spectra. The order parameter profiles of the phospholipid acyl chains could be attributed to slow fluctuations of the whole membrane and to detergent-induced local perturbations of the bilayer order. The packing constraints in the mixed bilayers that eventually lead to bilayer solubilization were reflected by the order parameters of the interfacial phospholipid acyl chain segments and of the phospholipid headgroup. These results are interpreted in terms of the changing average shape of the component molecules. Considering the decreasing cross sectional areas in the acyl chain region and the increasing hydration of the detergent headgroups, the bilayer-micelle transition is the result of an imbalance in the chain and headgroup repulsion. A neutral or pivotal plane can be defined on the basis of the temperature dependence of the interfacial quadrupolar splittings.     

Packing characteristics of highly unsaturated bilayer lipids: Raman spectroscopic studies of multilamellar phosphatidylcholine dispersions

The thermotropic properties and acyl chain packing characteristics of multilamellar dispersions of highly unsaturated lipids were examined by Raman spectroscopy. Bilayer assemblies were composed of POPC (1-palmitoyl-2-oleoylphosphatidylcholine), PAPC (1-palmitoyl-2-arachidonylphosphatidylcholine), and PDPC (1-palmitoyl-2-docosahexaenoylphosphatidylcholine), lipid systems possessing saturated sn-1 chains and unsaturated sn-2 chains with one, four, and six double bonds, respectively. Raman spectra were recorded in the acyl chain 2800-3100-cm-1 carbon-hydrogen (C-H) stretching and 1100-1200-cm-1 carbon-carbon (C-C) stretching mode regions, spectral intervals reflecting both the inter- and intrachain order/disorder properties of the various lipid dispersions. In order to obtain C-H stretching mode spectra relevant solely to the sn-1 chains of PAPC and PDPC, liquid-phase spectra of arachidonic and docosahexaenoic acid, respectively, were subtracted from the observed phospholipid spectra. The unsaturated sn-2 chains of PAPC and PDPC undergo minimal conformational reorganizations as the bilayers pass from the gel to liquid-crystalline phases. Phase transition temperatures, Tm, derived from statistically fitting the temperature-dependent Raman spectral data are approximately -2.5, -22.5, and -3 degrees C for POPC, PAPC, and PDPC, respectively. As the degree of unsaturation increases from POPC to PAPC and PDPC, the cooperativity of the phase transition, as measured by its breadth, decreases. Estimates of the transition widths from the temperature profiles are approximately 15 degrees C for PAPC and 20 degrees C for PDPC. The behavior of various Raman spectral parameters for the lipid gel phase reflects the formation of lateral microdomains, or clusters, whose packing properties maximize the van der Waals interactions between sn-1 chains.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of Langmuir-Blodgett films of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine and 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphat idylcholine by FTIR-ATR

Monomolecular films of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphatidylc holine (PPDPC) were transferred from an air/water interface onto a germanium attenuated total reflection crystal by the Langmuir-Blodgett (LB) technique. The assemblies were thereafter investigated by Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy. To determine the molecular organization in the deposited layers we monitored the CH2 and C = O stretching and the CH2 bending regions of the infrared spectra of these lipids in detail. Using Fourier self-deconvolution technique, the carbonyl stretching mode was resolved into two models corresponding to the conformational differences in the ester linkages of the phospholipid sn-1 and sn-2 acyl chains. By varying the temperature of the subphase and using different surface pressures, we were able to transfer different conformational states of DPPC onto a germanium ATR crystal. Deposition of DPPC at 40 mN m-1 and at 15 degrees C or at 20 mN m-1 and at 35 degrees C results in LB-assemblies in ordered or disordered states, respectively, as judged by the IR spectra. These structures in LB films correspond to the state of DPPC in liposomes below and above the temperature of the order-disorder phase transition. Irrespective of the surface pressure and subphase temperature used during the deposition, an ordering process was found in DPPC films when the number of the transferred layers was increased from one to five. The pyrene-labelled phosphatidylcholine analogue, PPDPC, behaved differently from DPPC. In the case where one to three layers of PPDPC transferred at 35 mN m-1 and at 20 degrees C only conformational structures resembling those in fully hydrated liposomes above the main transition temperature were observed.     

Fourier transform infrared studies of secondary structure and orientation of pulmonary surfactant SP-C and its effect on the dynamic surface properties of phospholipids

SP-C, a highly hydrophobic, 3.7-kDa protein constituent of lung surfactant, has been isolated from bovine lung lavage, purified, and reconstituted into binary lipid mixtures of 1,2-dipalmitoyl-phosphatidylcholine (DPPC) and 1,2-dipalmitoylphosphatidylglycerol (DPPG). Fourier transform infrared (FT-IR) spectroscopy has been applied to examine SP-C secondary structure, the average orientation of alpha-helical segments relative to the bilayer normal in membrane films, and the effect of protein on the thermotropic properties of the phospholipid acyl chains. In addition, dynamic surface measurements were made on phospholipid films at the A/W interface in the presence and absence of SP-C. SP-C (0.5 mol %) was found to possess about 60% alpha-helical secondary structure in lipid vesicles. Higher levels (1.5 mol %) of SP-C resulted in a slight increase of beta-forms, possibly resulting from protein aggregation. The helical segments exhibited an average angle of orientation of about 24 degrees with respect to the bilayer normal, suggesting a trans-bilayer orientation of the peptide. The observation that 70% of the peptide bond hydrogens are hard to exchange in D2O further reflects the hydrophobic nature of the molecule. SP-C produced little effect on the thermotropic properties of the binary lipid mixture, as measured from acyl chain C-H and C-D stretching frequencies. However, the presence of 1 mol % protein markedly reduced the viscance and increased the elasticity of surface films suggesting a mechanism by which SP-C facilitates the spreading of phospholipids on an aqueous surface. The possible physiological consequences of these observations are discussed.     

Structure and dynamics of dimyristoylphosphatidic acid/calcium complexes by 2H NMR, infrared, spectroscopies and small-angle x-ray diffraction

The structural and dynamic properties of complexes of dimyristoylphosphatidic acid (DMPA) and calcium ions have been characterized by 2H NMR, Raman, and infrared spectroscopies and small-angle X-ray diffraction. All techniques used show that these complexes do not undergo a cooperative thermotropic phase transition. Small-angle X-ray diffraction unambiguously demonstrates that the structure of the lipid molecules of the DMPA/Ca2+ complexes remains lamellar even at a temperature as high as 85 degrees C. Raman results indicate that within this temperature range, only a few trans-gauche isomerizations of the C-C bonds of the phospholipid acyl chains arise in this system. The 2H NMR spectra indicate that the DMPA chains are highly motionally restricted up to 65 degrees C and that higher temperatures might activate some low-frequency overall motions of entire lamellar domains. Small-angle X-ray scattering and 2H NMR spectroscopy of 2H2O also show that the interaction of calcium with DMPA promotes an important dehydration of the lipid assembly, even though the latter technique clearly demonstrates that some water molecules remain strongly bond in the DMPA/Ca2+ complexes. The carbonyl stretching mode region of the infrared spectrum of DMPA/Ca2+ complexes suggests that these water molecules are trapped near the interfacial region of the lipid membrane and are hydrogen bonded with the carbonyl groups of the lipid. Finally, comparison of the phosphate stretching mode region of the infrared spectra of complexes of DMPA with calcium ions with those of model compounds provides strong evidence that calcium ions bind to both charges of the phosphate group of DMPA and form bridges between adjacent bilayers.     

The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Temperature-dependence of microsomal enzyme activity and thermotropic changes in membrane structure.

Arrhenius plots of the non-latent UDP-glucuronyltransferase (p-nitrophenol acceptor) activity of guinea-pig microsomal membranes prepared with 154 mM-KCl were linear from 5 to 40 degrees C. Arrhenius plots for other microsomal preparations from guinea pig and rat liver that show various degrees of transferase latency, exhibited two linear regions intersecting at a sharp transition point near 20-25 degrees C. This discontinuity was abolished or greatly decreased when transferase latency was removed by treating the membranes with perturbants of phospholipid bilayer strucutre. The fluorescent probe N-phenyl-1-naphthyl-amine detected a thermotropic change in the fluidity of the phospholipid acyl chains of all the microsomal membrane preparations studied, at temperatures close to those of the Arrhenius-plot transitions. It is concluded that the thermotropic change in the structure of the membrane bilayer probably is a 'phase separation' or clustering of phospholipids, which affects a permeability barrier that restricts access of substrate to the transferase molecules.     

Thermotropic phase behavior of model membranes composed of phosphatidylcholines containing omega-cyclohexyl fatty acids. Differential scanning calorimetric and 31P NMR spectroscopic studies

The thermotropic phase behavior of aqueous dispersions of 10 phosphatidylcholines containing omega-cyclohexyl-substituted acyl chains was studied by differential scanning calorimetry and 31P nuclear magnetic resonance spectroscopy. The presence of the omega-cyclohexyl group has a profound effect on the thermotropic phase behavior of these compounds in a manner dependent on whether the fatty acyl chains have odd- or even-numbered linear carbon segments. The thermotropic phase behavior of the odd-numbered phosphatidylcholines is characterized by a single heating endotherm that was shown to be a superposition of at least two structural events by calorimetric cooling experiments. 31P NMR spectroscopy also showed that the single endotherm of the odd-chain compounds is the structural equivalent of a concomitant gel-gel and gel to liquid-crystalline phase transition. The calorimetric behavior of the even-numbered phosphatidylcholines is characterized by a complex array of gel-state phenomena, in addition to the chain-melting transition, in both the heating and cooling modes. The gel states of these even-numbered compounds are characterized by a relatively greater mobility of the phosphate head group as seen by 31P NMR spectroscopy. The differences between the odd-numbered and even-numbered compounds are reflected in a pronounced odd-even alternation in the characteristic transition temperatures and enthalpies and in differences in their responses to changes in the composition of the bulk aqueous phase. Moreover, both the odd-numbered and even-numbered omega-cyclohexylphosphatidylcholines exhibit significantly lower chain-melting transition temperatures and enthalpies than do linear saturated phosphatidylcholines of comparable chain length.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of cis and trans unsaturation on the structure of phospholipid bilayers: a high-pressure infrared spectroscopic study

In order to compare the effects of cis and trans unsaturation on the structure and packing of phospholipid bilayers, infrared spectra of aqueous dispersions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dielaidoyl-sn-glycero-3-phosphocholine (DEPC) were measured in a diamond anvil cell at 28 degrees C as a function of pressure up to 36 kbar. The infrared spectra indicate that DEPC and DOPC undergo pressure-induced liquid-crystalline to gel phase transitions at critical pressures of 0.7 and 5.2 kbar, respectively. Below their respective critical pressures, the infrared spectra of DOPC and DEPC are essentially indistinguishable, whereas above these pressures, there are very pronounced differences in the barotropic behavior of these two lipids. Specifically, at the 5.2-kbar transition in DOPC, there are significant changes in the frequencies, intensities, and widths of bands associated with the interfacial C = O groups, the olefinic CH = CH groups, and the terminal CH3 groups, whereas the corresponding bands of DEPC are, by contrast, relatively insensitive to the pressure-induced phase transition. The unusual band shape changes in DOPC are attributed to a unique packing arrangement of the oleoyl acyl chains required to accommodate the bent geometries of adjacent cis double bonds. Moreover, above 5 kbar in DEPC, well-defined correlation field splittings of the CH2 scissoring and rocking modes are observed, with magnitudes very similar to those observed at comparable pressures in saturated lipid systems. The absence of correlation field splittings of the corresponding bands of DOPC up to 36 kbar suggests that the bent oleoyl acyl chains are closely packed with all chains oriented parallel to each other.     

Conformational analysis of phosphatidylethanol-amine in multilayers by infrared dichroism.

Built-up films of L-alpha-dipalmitoyl phosphatidylethanolamine were prepared. Infrared dichroism was measured for the sample and analysed by a new method. This method has been developed for the determination of the directions of transition moments in a film sample, in which there is an axis of symmetry of perpendicular to the film plane. The directions of transition moments were determined for the six vibrations assigned to the CH2 antisymmetric stretching, CH2 symmetric stretching, CH2 scissoring, C=O stretching, PO2- antisymmetric stretching, and C-C-N+ antisymmetric stretching modes. The results indicate that hydrocarbon chains are inclined at about 75 degrees to the film plane and the polar groups orient parallel to the plane in the builtup film. A structural model of the phosphatidylethanolamine in the built-up film is proposed.     

A Fourier-transform infrared spectroscopic study of the polymorphic phase behavior of 1,2- bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine; a polymerizable lipid which forms novel microstructures

We have investigated the phase characteristics of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC23PC), a phosphatidylcholine with diacetylenic groups in the acyl chains, and its saturated analog 1,2-ditricosanoyl-sn-glycero-3-phosphocholine (DTPC), using Fourier-transform infrared spectroscopy (FTIR). Previous studies on the phase behavior of DC23PC in H2O have shown that DC23PC exhibits: (1) formation of cylindrical structures ('tubules') by cooling fluid phase multilamellar vesicles (MLVs) through Tm (43 degrees C), and 2) metastability of small unilamellar vesicles (SUVs) in the liquid-crystalline state some 40 degrees C below Tm, with subsequent formation of a gel phase comprised of multilamellar sheets at 2 degrees C. The sheets form tubules when heated and cooled through Tm. FTIR results presented here indicate that as metastable SUVs are cooled toward the transition to bilayer sheets, spectroscopic changes occur before the calorimetric transition as measured by a reduction in the CH2 symmetric stretch frequency and bandwidth. In spite of the vastly different morphologies, the sheet gel phase formed from SUVs is spectroscopically similar to the tubule gel phase. The C-H stretch region of DC23PC gel phase shows bands at 2937 and 2810 cm-1 not observed in the saturated analog of DC23PC, which may be related to perturbations in the acyl chains introduced by the diacetylenic moiety. The narrow CH2 scissoring mode at 1470 cm-1 and the prominent CH2 wagging progression indicate that DC23PC gel phase was highly ordered acyl chains with extended regions of all-trans methylene segments. In addition, the 13 cm-1 reduction in the C = O stretch frequency (1733-1720 cm-1) during the induction of DC23PC gel phase indicates that the interfacial region is dehydrated and rigid in the gel phase.     

Investigations into the polymorphism of lipid A from lipopolysaccharides of Escherichia coli and Salmonella minnesota by Fourier-transform infrared spectroscopy

The polymorphism of lipid A, the endotoxic principle of the lipopolysaccharides of gram-negative bacteria, has been investigated in the fully hydrated state at temperatures between 5 degrees and 58 degrees C via Fourier-transform infrared spectroscopy. These measurements were supplemented by X-ray diffraction, fluorescence intensity techniques and differential thermal analysis. Up to three distinct phase transitions could be detected, with the main transition temperatures lying at approximately 41 degrees, 46 degrees, 44 degrees and 47 degrees C for Escherichia coli lipid A, Salmonella minnesota lipid A, and the synthetic lipid A compounds 506 and 516, respectively. 4'-Monophosphoryl-lipid A samples exhibited their main transition temperatures at considerably higher temperatures (about 52 degrees C for E. coli lipid A). The analysis of greater than CH2 stretching absorption bands as well as the wide-angle scattering behaviour of the lipid A samples showed that the main transition apparently involved the completion of hydrocarbon chain melting of lipid A, as typically observed for phospholipids. However, the phase transition behaviour was found to be much more complex than that usually observed for model phospholipid systems. Even below the main transition temperature, considerable amounts of the methylene segments of the acyl chains of lipid A were found to assume gauche conformations. These conformational changes might be related to the occurrence of up to two further transitions located at about 22 degrees, 30 degrees, 27 degrees and 25.5 degrees C (first transition) and at about 34 degrees, 42 degrees, 38.5 degrees and 40.5 degrees C (second transition) for E. coli lipid A, S. minnesota lipid A and the synthetic lipid A compounds 506 and 516, respectively. Furthermore, by the analysis of some characteristic infrared absorption bands related to the hydrophilic backbone, it could be demonstrated that the temperature-induced conformational changes occurring within the hydrocarbon chains were constantly and simultaneously accompanied by detectable rearrangements within the interfacial region and the polar head group of lipid A. The following conclusions were drawn: Up to about 30 degrees C the lipid A assemblies were supposed to adopt virtually bilayered, true lamellar arrangements, as revealed by the analysis of greater than CH2 scissoring vibrations and X-ray diffraction pattern. However, as indicated by fluorometric techniques, no stable closed vesicles seemed to be formed even under these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)     

蟾毒灵与脂膜相互作用的研究

应用＾１３Ｃ－ＣＰ／ＭＡＳ和ＤＳＣ方法研究蟾毒灵与磷脂膜相互作用的执致相变特性及动力学特性。ＤＳＣ曲线表明蟾毒灵使磷脂膜相变温度降低,吸热峰变宽。＾１３Ｃ－ＣＰ／ＭＡＳ谱表明磷脂膜的ＮＭＲ信号峰化学位移随温度稍有变化,提示磷脂膜在液晶态脂肪烃链有不同程序的反－旁式异构化。含蟾毒灵的ＥＰＣ脂双层ＮＭＲ谱,随温度升高有蟾毒灵信号峰出现,ＥＰＣ脂双层分子内各部分的信号峰强度和峰形变化明显,说明脂双层分子