Miscibility of DPPC and DPPA in monolayers at the air/water interface

Monolayers of mixtures of 1,2-dipalmitoylphosphatidylcholine (DPPC) as the substrate and 1,2-dipalmitoylphosphatidic acid (DPPA) as the product of the hydrolysis reaction catalyzed by phospholipase D (PLD) were investigated in the presence of Ca2+. The miscibility behavior and the microstructure of mixed domains have been studied by grazing incidence X-ray diffraction (GIXD), Brewster angle microscopy and film balance measurements. The phase diagram reveals partial miscibility on both sides and a wide miscibility gap, which becomes narrower at high pressure. At low pressure, the segregation of condensed DPPA-rich domains in a fluid-like DPPC matrix was detected already at small DPPA concentrations and their structure was determined. A small amount of DPPC mixed into the segregated DPPA domains induces the transformation from rectangular to an oblique unit cell and increases the tilt angle in the condensed domains. At high pressure, two types of condensed phase domains were found: DPPC-rich and DPPA-rich. A drastic reduction of the tilt angle in the DPPC-rich domains with increasing amount of DPPA was observed. The decrease of the tilt angle must be connected with a change of the head group conformation of DPPC in such mixed domains.     

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.     

Behavior of a GPI-anchored protein in phospholipid monolayers at the air-water interface

The interaction between alkaline phosphatase (AP), a glycosylphosphatidylinositol (GPI)-anchored protein (AP-GPI), and phospholipids was monitored using Langmuir isotherms and PM-IRRAS spectroscopy. AP-GPI was injected under C16 phospholipid monolayers with either a neutral polar head (1,2-dipalmitoyl-sn-glycero-3-phosphocholine monohydrate (DPPC)) or an anionic polar head (1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS)). The increase in molecular area due to the injection of protein depended on the surface pressure and the type of phospholipid. At all surface pressures, it was highest in the case of DPPS monolayers. The surface elasticity coefficient E, determined from the pi-A diagrams, allowed to deduct that the AP-GPI-phospholipid mixtures presented a molecular arrangement less condensed than the corresponding pure phospholipid films. PM-IRRAS spectra suggested different protein-lipid interactions as a function of the nature of the lipids. AP-GPI modified the organization of the DPPS deuterated chains whereas AP-GPI affected only the polar group of DPPC at low surface pressure (8 mN/m). Different protein hydration layers between the DPPC and DPPS monolayers were suggested to explain these results. PM-IRRAS spectra of AP-GPI in the presence of lipids showed a shape similar to those collected for pure AP-GPI, indicating a similar orientation of AP-GPI in the presence or absence of phospholipids, where the active sites of the enzyme are turned outside of the membrane.     

Association of acylated cationic decapeptides with dipalmitoylphosphatidylserine-dipalmitoylphosphatidylcholine lipid membranes.

The interaction of three acylated and cationic decapeptides with lipid membranes composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylserine (DPPS) has been studied by means of fluorescence spectroscopy and differential scanning calorimetry (DSC). The synthetic model decapeptides that are N-terminally linked with C(2), C(8), and C(14) acyl chains contain four basic histidine residues in their identical amino acid sequence. A binding model, based on changes in the intrinsic fluorescent properties of the peptides upon association with the DPPC-DPPS membranes, is used to estimate the peptide-membrane dissociation constants. The results clearly show that all three peptides have a higher affinity to liposomes containing DPPS lipids due to non-specific electrostatic interactions between the cationic peptides and the anionic DPPS lipids. Furthermore, it is found that the acyl chain length of the peptides plays a crucial role for the binding. A preference for fluid phase membranes as compared to gel phase membranes is generally observed for all three peptides. DSC is used to characterise the influence of the three peptides on the thermodynamic phase behaviour of the binary DPPC-DPPS lipid mixture. The extent of peptide association deduced from the heat capacity measurements suggests a strong binding and membrane insertion of the C(14) acylated peptide in accordance with the fluorescence measurements.     

Thermal stability and DPPC/Ca2+ interactions of pulmonary surfactant SP-A from bulk-phase and monolayer IR spectroscopy.

Surfactant protein A (SP-A), the most abundant pulmonary surfactant protein, is implicated in multiple biological functions including surfactant homeostasis, biophysical activity, and host defense. SP-A forms ternary complexes with lipids and Ca2+ which are important for protein function. The current study uses infrared (IR) transmission spectroscopy to investigate the bulk-phase interaction between SP-A, 1,2-dipalmitoylphosphatidylcholine (DPPC), and Ca2+ ions along with IR reflection-absorption spectroscopy (IRRAS) to examine protein secondary structure and lipid orientational order in monolayer films in situ at the air/water interface. The amide I contour of SP-A reveals two features at 1653 and 1636 cm(-1) arising from the collagen-like domain and a broad feature at 1645 cm(-1) suggested to arise from the carbohydrate recognition domain (CRD). SP-A secondary structure is unchanged in lipid monolayers. Thermal denaturation of SP-A in the presence of either DPPC or Ca2+ ion reveals a sequence of events involving the initial melting of the collagen-like region, followed by formation of intermolecular extended forms. Interestingly, these spectral changes were inhibited in the ternary system, showing that the combined presence of both DPPC and Ca2+ confers a remarkable thermal stability upon SP-A. The ternary interaction was revealed by the enhanced intensity of the asymmetric carboxylate stretching vibration. The IRRAS measurements indicated that incorporation of SP-A into preformed DPPC monolayers at a surface pressure of 10 mN/m induced a decrease in the average acyl chain tilt angle from 35 degrees to 28 degrees. In contrast, little change in chain tilt was observed at surface pressures of 25 or 40 mN/m. These results are consistent with and extend the fluorescence microscopy studies of Keough and co-workers [Ruano, M. L. F., et al. (1998) Biophys. J. 74, 1101-1109] in which SP-A was suggested to accumulate at the liquid-expanded/liquid-condensed boundary. Overall these experiments reveal the remarkable stability of SP-A in diverse, biologically relevant environments.     

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.     

Interaction of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine-d54 mixtures with glycophorin. A fourier transform infrared investigation

Glycophorin from the human erythrocyte membrane has been isolated in pure form and reconstituted into large unilamellar vesicles comprised of binary mixtures of 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC) and chain perdeuterated 1,2-dimyristoyl-3-sn-phosphatidylcholine (DMPC-d54). The effect of temperature and protein on lipid structure and mixing was monitored by using Fourier transform infrared spectroscopy; deuteration of one of the components of the mixture permits observation of the protein interaction with each lipid species. The melting curves were analyzed by assuming that each lipid chain can exist in one of two physical states (i.e., gel or liquid crystalline), characterized by a temperature-dependent Lorentzian distribution for the line shape of the C-H or C-D stretching vibrations. The fraction of each lipid component melted at temperatures within the two-phase region of the phase diagram was calculated and approximate phase diagrams were constructed. Addition of protein lowers the liquidus line of the phase diagram while leaving the solidus line essentially unchanged. No lipid phase separation is observed. The effect of protein is more pronounced on the DPPC component than on the DMPC-d54. The former is significantly more disordered and/or fluidized at all lipid mole fractions in the ternary system than in the binary phospholipid mixture.     

Ca(2+)-responsive extensible monolayer membrane of calmodulin-albumin conjugate.

A Ca(2+)-responsive monolayer protein membrane was prepared by developing calmodulin and bovine serum albumin at the air-water interface and by conjugating them with a bifunctional agent. In the case of the BSA monolayer, complex formation with Mg2+ generated a larger change in surface pressure than that with Ca2+. On the other hand, a drastic change in surface pressure was observed for the conjugated thin membrane associated with Ca2+ than that associated with Mg2+. Due to a drastic change in the conformation of calmodulin, the conjugated protein film changes its morphology (STM image), depending on Ca2+ concentration: the extended structure in the presence of Ca2+ transforms to a shrinked structure in the absence of Ca2+. The largest surface pressure change was detected when calmodulin was mixed with an equimolar amount of bovine serum albumin.     

Infrared spectroscopic investigations of pulmonary surfactant. Surface film transitions at the air-water interface and bulk phase thermotropism.

The molecular structure of the phospholipid component of intact pulmonary surfactant isolated from bovine lung lavage has been examined by Fourier transform infrared spectroscopy. Two different physical states of the surfactant were examined by means of different infrared spectroscopic sampling techniques. Transmission infrared experiments were used to study the surfactant in the bulk phase. In these experiments, the thermotropic behavior of the bulk surfactant was monitored by temperature-induced variations in the phospholipid acyl chain CH2 stretching frequencies. A broad phase transition (confirmed by differential scanning calorimetry) was noted with an onset temperature near 15 degrees C and a completion temperature near 42 degrees C. In addition to the bulk transmission experiments, external reflection infrared spectroscopy was used to examine surfactant films in situ at the air-water interface. As surface pressure was increased from 0 to 43 dyn/cm, a gradual and continuous decrease in the CH2 stretching frequency was noted for the surfactant. Thus, under surface pressures which correspond to large lung volumes in vivo, the surfactant acyl chains exist mostly in the ordered (trans) configuration. The frequency shift in the CH2 stretching mode is consistent with a continuous ordering of the acyl chains upon compression over the pressure range 0-43 dyn/cm, and implies that a weakly cooperative phase transition occurs in the hydrocarbon region of the surface film. The surface film transition is especially noted in the pressure-area curve of the surfactant and approximates in two dimensions the broad thermotropic phase transition of the bulk phase surfactant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of cholesterol on conformational disorder in dipalmitoylphosphatidylcholine bilayers. A quantitative IR study of the depth dependence

A method originally proposed by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of trans-gauche isomerization in hydrocarbon chains and recently applied [Mendelsohn et al. (1989) Biochemistry 28, 8934-8939] to the quantitative determination of phospholipid acyl chain conformational order is utilized to monitor the effects of cholesterol at various depths in dipalmitoylphosphatidylcholine (DPPC) bilayers. The method is based on the observation that the CD2 rocking modes from the acyl chains of specifically deuterated phospholipids occur at frequencies in the Fourier transform infrared spectrum which depend upon the local geometry (trans or gauche) of the C-C-C skeleton surrounding a central CD2 group. Three specifically deuterated derivatives of DPPC, namely, 4,4,4',4'-d4 DPPC (4-d4 DPPC), 6,6,6',6'-d4 DPPC (6-d4 DPPC), and 12,12,12',12'-d4 DPPC (12-d4 DPPC), have been synthesized, and the effects of cholesterol addition at 2:1 DPPC/cholesterol (mol:mol) on acyl chain order at various temperatures have been determined. At 48 degrees C, cholesterol inhibits gauche rotamer formation by factors of approximately 9 and approximately 6 at positions 6 and 4, respectively, of the acyl chains, thus demonstrating a strong ordering effect in regions of the bilayer where the sterol rings are presumed to insert parallel to the DPPC acyl chains. In contrast, the ability of the sterol to order the acyl chains is much reduced at the 12-position. The sterol demonstrates only a slight disordering of phospholipid gel phases. Finally, the contributions of different classes of gauche conformers to the spectra have been determined.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modifying dipalmitoylphosphatidylcholine monolayers by n-hexadecanol and dipalmitoylglycerol

The monolayer structure of pure dipalmitoylphosphatidylcholine (DPPC) and equimolar mixtures of DPPC/n-hexadecanol (C(16)OH) and DPPC/dipalmitoylglycerol (DPG) are studied by the film balance technique and grazing incidence X-ray diffraction measurements. At 20 degrees C, the binary systems exhibit complete miscibility. In contrast to pure DPPC monolayers, a condensing effect is observed in the presence of both non-phospholipid additives; but the phase transition behavior differs. The tilt angle of the hydrocarbon chains in the DPPC/C(16)OH mixture is significantly smaller than in pure DPPC monolayers. The tilt of the chains is even further reduced in the mixed monolayer of DPPC/DPG. A comparison of the three systems reveals distinct structural features such as phase state, chain tilt, and molecular area over a wide range of surface pressures. Therefore, these monolayers provide a highly suitable model to investigate the influence of structural parameters on biological processes occurring at the membrane surface, e.g. enzymatic reactions and adsorption events.     

Structural investigation on the adsorption of the MARCKS peptide on anionic lipid monolayers - effects beyond electrostatic

The presence of charged lipids in the cell membrane constitutes the background for the interaction with numerous membrane proteins. As a result, the valence of the lipids plays an important role concerning their lateral organization in the membrane and therefore the very manner of this interaction. This present study examines this aspect, particularly regarding to the interaction of the anionic lipid DPPS with the highly basic charged effector domain of the MARCKS protein, examined in monolayer model systems. Film balance, fluorescence microscopy and X-ray reflection/diffraction measurements were used to study the behavior of DPPS in a mixture with DPPC for its dependance on the presence of MARCKS (151-175). In the mixed monolayer, both lipids are completely miscible therefore DPPS is incorporated in the ordered crystalline DPPC domains as well. The interaction of MARCKS peptide with the mixed monolayer leads to the formation of lipid/peptide clusters causing an elongation of the serine group of the DPPS up to 7? in direction to surface normal into the subphase. The large cationic charge of the peptide pulls out the serine group of the interface which simultaneously causes an elongation of the phosphodiester group of the lipid fraction too. The obtained results were used to compare the interaction of MARCKS peptide with the polyvalent PIP(2) in mixed monolayers. On this way we surprisingly find out, that the relative small charge difference of the anionic lipids causes a significant different interaction with MARCKS (151-175). The lateral arrangement of the anionic lipids depends on their charge values and determines the diffusion of the electrostatic binding clusters within the membrane.     

膜脂的物理状态对G_s激活AC的影响

用生物膜的拆离与重建方法将从牛脑皮层膜中纯化的激活型ＧＴＰ结合蛋白（Ｇｓ）和腺苷酸环化酶（ＡＣ）在含有不同极性头部或不同脂肪酸侧链的磷脂组成的脂质体上重建形成脂酶体,测定脂酶体中ＡＣ的基础活力及Ｇｓ激活ＡＣ的活力。实验结果表明,磷脂影响ＡＣ的基础活力和Ｇｓ激活ＡＣ活力的顺序依次为：ＰＥ＞ＰＳ＞ＰＣ;含不同脂肪酸侧链的混合磷脂对Ｇｓ的激活活力的影响大于含单一脂肪酸侧链的纯磷脂,如ＰＥＤＰＰＥ,ＰＳＤＰＰＳ,ＰＣＤＰＰＣ。含不同脂肪酸侧链的磷脂影响Ｇｓ的活力的顺序为ＤＬＰＣ＞ＤＭＰＣ＞ＤＰＰＣ。用反映磷脂分子的堆积程度的荧光探剂ＭＣ５４０和脂双层的流动性变化的ＤＰＨ以及专一性标记蛋白质巯基（－ＳＨ）基团的荧光探剂ａｃｒｙｌｏｄａｎ的测定结果表明,不同磷脂影响Ｇｓ的活力的差异主要是由于脂质物理状态的不同所致。     

The psychotropic drug olanzapine (Zyprexa) increases the area of acid glycerophospholipid monolayers

The typical antipsychotics chlorpromazine (CPZ) and trifluoperazine (TFP) increase the mean molecular area (mma) of acidic, but not neutral, glycerophospholipids in monolayers at pH 7.36 measured by the Langmuir technique. The atypical antipsychotic olanzapine (OLP(1)) is structurally similar to TFP. We have therefore studied the effects of OLP on glycerophospholipid monolayers and in comparison with CPZ. Olanzapine (10 microM, in subphase, pH 7.36) influenced the isotherms (surface pressure versus mma) in monolayers of the neutral dipalmitoyl phosphatidylcholine (DPPC) and the acidic dipalmitoyl phosphatidylserine (DPPS) or 1-palmitoyl-2-oleoylphosphatidylserine (POPS) in the increasing order of mma: DPPS相似文献   

Molecular organization of surfactin-phospholipid monolayers: effect of phospholipid chain length and polar head

Mixed monolayers of the surface-active lipopeptide surfactin-C(15) and various lipids differing by their chain length (DMPC, DPPC, DSPC) and polar headgroup (DPPC, DPPE, DPPS) were investigated by atomic force microscopy (AFM) in combination with molecular modeling (Hypermatrix procedure) and surface pressure-area isotherms. In the presence of surfactin, AFM topographic images showed phase separation for each surfactin-phospholipid system except for surfactin-DMPC, which was in good agreement with compression isotherms. On the basis of domain shape and line tension theory, we conclude that the miscibility between surfactin and phospholipids is higher for shorter chain lengths (DMPC>DPPC>DSPC) and that the polar headgroup of phospholipids influences the miscibility of surfactin in the order DPPC>DPPE>DPPS. Molecular modeling data show that mixing surfactin and DPPC has a destabilizing effect on DPPC monolayer while it has a stabilizing effect towards DPPE and DPPS molecular interactions. Our results provide valuable information on the activity mechanism of surfactin and may be useful for the design of surfactin delivery systems.     

Distinct steps in the adsorption of pulmonary surfactant to an air-liquid interface

To investigate the mechanisms by which vesicles of pulmonary surfactant adsorb to an air-liquid interface, we measured the effect of different phospholipids and of their concentration both in the subphase and at the interface on this process. Adsorbing vesicles contained the hydrophobic surfactant proteins mixed with the following four sets of surfactant phospholipids that varied the content of anionic headgroups and mixed acyl chains independently: the complete set of purified phospholipids (PPL) from calf surfactant; modified PPL (mPPL) from which the anionic phospholipids were removed; a mixture of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG) (9:1, mol:mol); and DPPC alone. The initial reduction in surface tension depended strongly on the anionic phospholipids and the subphase concentration. The acyl groups had no effect. Adsorption beyond the initial stage depended more on the mixed acyl groups, became increasingly independent of subphase concentration, and was determined instead by the interfacial concentration of the surface film. The different constituents produced the same effects in vesicles adsorbing to a clean interface or in a preexisting film to which vesicles of SP:DPPC adsorbed. Adsorption for vesicles of SP:PPL adsorbing to DPPC or of SP:DPPC to PPL above a certain threshold surface concentration followed exactly the same isotherm. Our results fit best with a two-step model for adsorption. The anionic phospholipids first promote the initial juxtaposition of vesicles to the interface. Compounds with mixed acyl constituents at the point of contact between vesicle and interface then facilitate fusion with the surface.     

Lipid model membranes for drug interaction study

The present work shows a structural study on the process of incorporation of a hydrophobic drug, Ellipticine (ELPT), into lipid model membranes for drug targeting purpose. The ELPT is an alkaloid that showed an anti-proliferation activity against several types of tumor cells and against the HIV1 virus. We used the zwitterionic lipid dipalmitoyl phosphatidylcholine (DPPC) and four different anionic lipids: cardiolipin (CL), dipalmitoyl phosphatidic acid (DPPA), dipalmitoyl phosphatidylglycerol (DPPG) and dipalmitoyl phosphatidylserine (DPPS), both spread on a Langmuir monolayer and deposited on a solid substrate to mimic a model membrane and study the interaction with the drug ELPT. X-ray reflectivity results pointed toward an increase in drug loading efficiency up to 13.5% mol/mol of ELPT into mixed systems DPPC/CL. This increase in loading efficiency was also accompanied by a slight distortion in the stacking of the bilayers less evidenced after optimization of the molar ratio between the co-lipids. Grazing incidence X-ray diffraction measurements revealed an in-plane lattice distortion due to the presence of hydrocarbon chain backbone ordering in pure systems of DPPC doped with ELPT. The same was not observed in mixed membranes with DPPC/CL and DPPC/DPPA.     

CD2 rocking modes as quantitative infrared probes of one-, two-, and three-bond conformational disorder in dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine/cholesterol mixtures

The use of CD2 rocking modes in the IR spectrum as quantitative probes of phospholipid conformational disorder has recently been described for aqueous dispersions of 1,2-dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol mixtures [Mendelsohn et al. (1989) Biochemistry 28, 8934-8939; Davies et al. (1990) Biochemistry 29, 4368-4373]. Initial studies focused at the 4, 6, and 10 acyl chain positions of DPPC. In the current work, the method is extended to the 2, 3, 12, and 13 positions. Conformational disorder in the L alpha phase is approximately the same (about 20% gauche) at positions 4, 10, and 13, but an unexpected higher value is observed (about 30%) at the 6 position. Cholesterol (33 mol%) restricts gauche rotamer formation by factors ranging from 6 to 9 at positions 4 and 6, respectively, to 1.5-2 at positions 10, 12, and 13. Quantitative analysis for the DPPC/cholesterol "liquid-ordered" phase indicates the occurrence of 1.2 gauche bonds/chain, a marked reduction from the 3.6-4.2 gauche bonds/chain for DPPC alone. Proximity to the ester moiety at acyl chain position 3 perturbs the vibrational coupling patterns of the CD2 rocking modes and eliminates their sensitivity to conformational change. In addition, the feasibility of a method based on the conformation-dependent coupling between CD2 rocking frequencies of two successive CD2 groups for the quantitative detection of specific, position-dependent king (gtg') and isolated gauche (gtt) conformers is demonstrated. Finally, comparisons between IR measurements and explicit theoretical predictions of acyl chain conformational order are presented.     

Influence of acylcarnitines of different chain length on pure and mixed phospholipid vesicles and on sarcoplasmic reticulum vesicles

Palmitoyl-, myristoyl- and lauroylcarnitine destabilize small unilamellar vesicles of 1,2-dipalmitoyl-n-glycero-3-phosphorylcholine (DPPC) and 1,2-dimyristoyl-n-glycero-3-phosphorylcholine (DMPC) into multilamellar liposomes. Their effect on the bilayer is dependent on the acyl chain length of the acylcarnitine, the ratio of the lengths of the acyl chains of the phospholipid and the acylcarnitine and the molar ratio of the phospholipid to acylcarnitine but not the absolute concentration of the acylcarnitine in the solute. Sarcoplasmic reticulum vesicles are broken down by each of the acylcarnitines at concentrations below their critical micellar concentrations (CMC). These three acylcarnitines stimulate the Mg2+, Ca2+-ATPase activity in SR-vesicles to a certain maximum, after which a net inhibition is observed. The maximum degree of stimulation depends highly on acyl chain length: the shorter the chain length, the more effective. In the same concentration range where the Mg2+, Ca2+-ATPase activity is increased, the net Ca2+-uptake is markedly decreased.