Angle of tilt and domain structure in dipalmitoyl phosphatidylcholine multilayers.

A cooperative alignment of lipid chains in dipalmitoyl phosphatidylcholine (DPPC) bilayers was detected by using oriented multilayers containing small amounts of spin-labeled phosphatidylcholine. It is shown that a significant angle of tilt exists along the entire length of the lipid chains in DPPC. This behavior is compared with that of the more complex egg phosphatidylcholine bilayers. The lipid chains do not have the alignment of a single crystal but evidently exist in domains consisting of either clusters within a bilayer or successive layers out of register in the stacked multilayer.     

Interactions of pyrethroids with phosphatidylcholine bilayers: comparisons in liposomal systems exhibiting large or small radii of curvature

Pyrethroid interactions with dipalmitoyl phosphatidylcholine (DPPC) vesicles have been characterized in bilayers having large and small radii of curvature. The abilities of pyrethroids to alter the gel-fluid phase transition profiles were determined by steady state fluorescence anisotropy and phase-modulation lifetime techniques using the fluorescent probes cis- and trans-parinaric acid. Using the geometric isomers of parinaric acid as membrane probes, pyrethroids were found to lower the phase transition temperature (Tc) of DPPC large multilamellar vesicles with the same order of comparative effectiveness as previously reported using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Permethrin had a greater depressive effect upon the Tc of DPPC in the small unilamellar vesicle (SUV) system than in the large multilamellar system. Conversely, allethrin was less effective in reducing the Tc of DPPC SUVs. The enhanced effect of permethrin in decreasing the Tc of DPPC SUVs was greatest in regions of more rigid lipid packing, as determined by trans-parinaric acid fluorescence parameters. The results indicate that changes in lipid packing configuration caused by differing bilayer radii of curvature may alter the interactive characteristics of pyrethroids with lipid membranes.     

Interactions of angiotensin II non-peptide AT(1) antagonist losartan with phospholipid membranes studied by combined use of differential scanning calorimetry and electron spin resonance spectroscopy.

We used differential scanning calorimetry (DSC) and electron spin resonance (ESR) spectroscopy to investigate the interactions of Losartan, a potent, orally active Angiotensin II AT(1) receptor antagonist with phospholipid membranes. DSC results showed that Losartan sensitively affected the chain-melting behavior of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayer membranes. ESR spectroscopy showed that phosphatidylcholines spin-labeled at the 5-position of the sn-2 acyl chain (n-PCSL with n=5), incorporated either in DMPC or DPPC bilayers containing Losartan, were restricted in motion both in the gel and in the liquid-crystalline membrane phases, indicating a location of the antagonist close to the interfacial region of the phosphatidylcholine bilayer. At high drug concentrations (mole fraction >/= x=0.60), the decrease in chain mobility registered by 5-PCSL in fluid-phase membranes is smaller than that found at lower concentrations, whereas that registered by 14-PCSL is further increased. This indicates a different mode of interaction with Losartan at high concentrations, possibly arising from a location deeper within the bilayer. Additionally, Losartan reduced the spin-spin broadening of 12-PCSL spin labels in the gel-phase of DMPC and DPPC bilayers. As a conclusion, our study has shown that Losartan interacts with phospholipid membranes by affecting both their thermotropic behavior and molecular mobility.     

Decreased lipid order induced by microsomal cytochrome P-450 and NADPH-cytochrome P-450 reductase in model membranes: fluorescence and electron spin resonance studies

Cytochrome P-450 and NADPH-cytochrome P-450 reductase were reconstituted in unilamellar lipid vesicles prepared by the cholate dialysis technique from pure dimyristoylphosphatidylcholine (DMPC), pure dipalmitoylphosphatidylcholine (DPPC), pure dioleoylphosphatidylcholine (DOPC), and phosphatidylcholine/phosphatidylethanolamine/phosphatidylserine (PC/PE/PS) (10:5:1). As probes for the vesicles' hydrocarbon region, 1,6-diphenyl-1,3,5-hexatriene (DPH) and spin-labeled PC were used. The steady-state and time-resolved fluorescence parameters of DPH were determined as a function of temperature and composition of liposomes. Incorporation of either protein alone or together increased the steady-state fluorescence anisotropy (rs) of DPH in DOPC and PC/PE/PS (10:5:1) liposomes. In DMPC and DPPC vesicles, the proteins decreased rs significantly below the transition temperature (Tc) of the gel to liquid-crystalline phase transition. Time-resolved fluorescence measurements of DPH performed in reconstituted PC/PE/PS and DMPC proteoliposomes showed that the proteins disorder the bilayer both in the gel and in the liquid-crystalline phase. Little disordering by the proteins was observed by a spin-label located near the mid-zone of the bilayer 1-palmitoyl-2-(5-doxylstearoyl)-3-sn-phosphatidylcholine (8-doxyl-PC), whereas pronounced disordering was detected by 1-palmitoyl-2-(8-doxylpalmitoyl)-3-sn-phosphatidylcholine (5-doxyl-PC), which probes the lipid zone closer to the polar part of the membrane. Fluorescence lifetime measurements of DPH indicate an average distance of greater than or equal to 60 A between the heme of cytochrome P-450 and DPH.     

Binding of divalent cations of dipalmitoylphosphatidylcholine bilayers and its effect on bilayer interaction

We have confirmed that CaCl2 swells the multilayer lattice formed by dipalmitolyphosphatidylcholine (DPPC) in an aqueous solution. Specifically, at room temperature 1 mM CaCl2 causes these lipid bilayers to increase their separation, dw, from 19 A in pure water to greater than 90 A. CaCl2 concentrations greater than 4 mM cause less swelling. We have measured the net repulsive force between the bilayers in 30 mM CaCl2 at T = 25 degrees C (below the acyl chain freezing temperature). For interbilayer separations between 30 and 90 A, the dominant repulsion between bilayers is probably electrostatic; Ca2+ binds to DPPc lecithin bilayers, imparting a charge to them. The addition of NaCl to CaCl2 solutions decreases this repulsion. For dw less than 20 A, the bilayer repulsion appears to be dominated by the "hydration forces" observed previously between both neutral and charged phospholipids. From the electrostatic repulsive force, we estimate the extent of Ca2+ binding to the bilayer surface. The desorption and bound Ca2+, apparent when bilayers are pushed together, is more rapid than one would expect if an association constant governed Ca2+ binding. The association affinity does not appear to be a fixed quantity but rather a sensitive function of ionic strength and bilayer separation.     

Ca~(2+)通过膜脂影响肌质网Ca~(2+)-ATP酶的活性与Ca~(2+)转运功能

重建在大豆磷脂脂质体上的兔骨骼肌肌质网Ca~(2+)—ATP酶在ATP驱动下可将溶液中的Ca~(2+)转运到脂酶体内部;外加EGTA则可除去脂酶体外部的Ca~(2+),由此可得到四种含Ca~(2+)状态不同的脂酶体:(1)内、外都无Ca~(2+);(2)仅外部有Ca~(2+);(3)内、外都有Ca~(2+);(4),仅内部有Ca~(2+).用DPH和AS系列萤光探针对这四种含Ca~+状态不同的脂酶体的膜脂流动性进行了测定,结果表明:脂酶体外部加入Ca~(2+),脂双层外表面的流动性降低.当Ca~(2+)进入脂酶体内部后,内表面膜脂的流动性也降低,而且外层膜脂流动性进一步降低.脂酶体内、外的Ca~(2+)含量不同时,Ca~(2+)—ATP酶功能状态也不同.转运到脂酶体内部的ca~(2+)积累到一定浓度后,通过Ca~(2+)泵向内转运的Ca~(2+)及Ca~(2+)—ATP酶活力都受到了抑制.转运进行到第四分钟时的酶活只有第一分钟的9%.但在相同的实验条件下,失去了完整的膜结构的纯化的Ca~(2+)—ATP酶蛋白没有被抑制.这提示完整的膜结构是这种抑制作用所必需的,而且膜两侧Ca~(2+)浓度的梯差可通过影响膜脂来调节Ca~(2+)—ATP酶的功能.     

The behaviors of Ca(2+)-ATPase embedded in interdigitated bilayer.

We investigated the behavior of a membrane protein, Ca(2+)-ATPase, in interdigitated phospholipid bilayers. The results showed that Ca(2+)-ATPase does not cause significant alterations in the interdigitation of 16:0 LPC/DPPC (27.0 mol% LPC) vesicles when it is reconstituted with lipids. Intrinsic fluorescence, acrylodan fluorescent adducts, and CD spectra indicated that Ca(2+)-ATPase, when embedded in interdigitated bilayer structures, is more exposed to the hydrophilic environment and has a looser structure than when embedded in non-interdigitated bilayers. The interdigitation of acyl chains induces a rapid loss of enzyme activity. It is suggested that interdigitated bilayer structures may play an important role as negative regulatory factors in physiological functions.     

Effect of lipid membrane structure on the adenosine 5'-triphosphate hydrolyzing activity of the calcium-stimulated adenosinetriphosphatase of sarcoplasmic reticulum

An active Ca2+-stimulated, Mg2+-dependent adenosinetriphosphatase (Ca2+-ATPase) isolated from rabbit skeletal muscle sarcoplasmic reticulum membranes has been incorporated into dilauroyl-, dimyristoyl-, dipentadecanoyl-, dipalmitoyl-, and palmitoyloleoylphosphatidylcholine bilayers by using a newly developed lipid-substitution procedure that replaces greater than 99% of the endogenous lipid. Freeze--fracture electron microscopy showed membranous vesicles of homogeneous size with symmetrically disposed fracture-face particles. Diphenylhexatriene fluorescence anisotropy was used to define the recombinant membrane phase behavior and revealed more than one transition in the membranes. Enzymatic analysis indicated that saturated phospholipid acyl chains inhibited both overall ATPase activity and Ca2+-dependent phosphoenzyme formation below the main lipid phase transition temperature (Tm) of the lipid-replaced membranes. At temperatures above Tm, ATPase activity but not phosphoenzyme formation was critically dependent on acyl chain length and thus bilayer thickness. No ATPase activity was observed in dilauroylphosphatidylcholine bilayers. Use of the nonionic detergent dodecyloctaoxyethylene glycol monoether demonstrated that the absence of activity was not due to irreversible inactivation of the enzyme. Increased bilayer thickness resulted in increased levels of activity. An additional 2-fold rise in activity was observed when one of the saturated fatty acids in dipalmitoylphosphatidylcholine was replaced by oleic acid, whose acyl chain has a fully extended length comparable to that of palmitic acid. These results indicate that the Ca2+-ATPase requires for optimal function a "fluid" membrane with a minimal bilayer thickness and containing unsaturated phospholipid acyl chains.     

Effect of calcium on phospholipid interaction with pulmonary surfactant protein C.

Porcine pulmonary surfactant-associated protein SP-C was incorporated into bilayers of chain-perdeuterated dipalmitoylphosphatidylglycerol (DPPG-d62) and chain-perdeuterated dipalmitoyl-phosphatidylcholine (DPPC-d62) and into bilayers containing 70 mol% dipalmitoyl-phosphatidylcholine (DPPC) and 30 mol% DPPG-d62 or 70 mol% DPPC-d62 and 30 mol% dipalmitoylphosphatidylglycerol (DPPG). The effect of SP-C on the phase behavior, lipid chain order, and dynamics in these bilayers was examined by using deuterium nuclear magnetic resonance. SP-C was found to have a similar effect on the chain order and phase behavior of DPPC-d62 and DPPG-d62 in bilayers with a single lipid component. In gel phase DPPC/DPPG (7:3) bilayers with one or the other lipid component chain-perdeuterated, SP-C was found to affect first spectral moment more strongly for DPPG-d62 than for DPPC-d62. This may indicate that SP-C induced a nonrandom lateral distribution in the mixed lipid bilayer. SP-C was also found to influence motions responsible for deuteron transverse relaxation in both the gel and liquid crystalline phases. The presence of 5 mM Ca2+ in the aqueous phase substantially altered the effect of SP-C on transverse relaxation in the bilayer.     

Mechanism of action of "ruthenium red" compounds on Ca2+ ionophore from sarcoplasmic reticulum (Ca2+ + Mg2+)- adenosine triphosphatase and lipid bilayer.

Sarcoplasmic reticulum (Ca2+ + Mg2+)-ATPase was previously shown to have Ca2+-dependent and -selective ionophoric activity when tested in oxidized cholesterol lipid bilayer membranes (Shamoo, A. E., and MacLennan, D. H. (1974) Proc. Natl. Acad. Sci. U. S. A. 71, 3522). ruthenium red, a known inhibitor of (Ca2+ + Mg2+)-ATPase, is found to inhibit the Ca2+-ionophoric activity associated with (Ca2+ + Mg2+)-ATPase. Furthermore, ruthenium red alone acts as an anion-selective ionophore in lipid bilayers with the the following selectivity sequence for anions: l- greater than Cl-, Br- greater than F- greater than NO3-. The PCl-/PNa+ ratio was approximately 4/l. The presence of ruthenium red in excess of Ca2+ ionophore in lipid bilayer experiments converts the cation selectivity of the bilayer due to Ca2+ ionophore into anion selectivity.     

Structural changes in dipalmitoylphosphatidylcholine bilayer promoted by Ca2+ ions: a small-angle neutron scattering study

Small-angle neutron scattering (SANS) curves of unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles in 1-60mM CaCl2 were analyzed using a strip-function model of the phospholipid bilayer. The fraction of Ca2+ ions bound in the DPPC polar head group region was determined using Langmuir adsorption isotherm. In the gel phase, at 20 degrees C, the lipid bilayer thickness, dL, goes through a maximum as a function of CaCl2 concentration (dL=54.4A at approximately 2.5mM of CaCl2). Simultaneously, both the area per DPPC molecule AL, and the number of water molecules nW located in the polar head group region decrease (DeltaAL=AL(DPPC))-AL(DPPC+Ca)=2.3A2 and Deltan=n(W(DPPC))-n(W(DPPC+Ca))=0.8mol/mol at approximately 2.5mM of CaCl2). In the fluid phase, at 60 degrees C, the structural parameters d(L), A(L), and n(W) show evident changes with increasing Ca2+ up to a concentration C(Ca)(2+) < or = 10mM. DPPC bilayers affected by the calcium binding are compared to unilamellar vesicles prepared by extrusion. The structural parameters of DPPC vesicles prepared in 60mM CaCl2 (at 20 and 60 degrees C) are nearly the same as those for unilamellar vesicles without Ca2+.     

Protein-lipid interaction. Biophysical studies of (Ca2+ + Mg2+)-ATPase reconstituted systems

Differential scanning calorimetry, fluorescence spectroscopy and freeze-fracture electron microscopy have been applied to a study of the reconstituted Ca2+-ATPase proteins from sarcoplasmic reticulum when they are incorporated into pure lipid/water systems. The results obtained with these techniques have been used to examine the effects of this intrinsic protein upon the surrounding lipid at temperatures above and below the main lipid solid-fluid phase transition temperature (Tc). 1. Above this Tc value, the freeze-fracture data show that the proteins are randomly distributed within the plane of the bilayer. The fluorescence data show that as the protein content in the bilayer increases, so does the 'microviscosity'. 2. Below Tc the proteins occur in high protein to lipid patches, separate from the remaining crystalline lipid. The fluorescence data indicate that at these temperatures the presence of the protein causes a decrease in microviscosity, whilst the calorimetric data indicate a decrease in enthalpy of the main lipid transition. 3. A premelting of the high protein to lipid patches formed by phase separation within the lipid bilayers is indicated by the calorimetric and fluorescence data. This observation is used to rationalise the 'anomalous' properties of the dipalmitoyl phosphatidylcholine-ATPase of exhibiting activity at temperatures well below the lipid phase transition at 41 degrees C.     

Effects of lindane on membrane fluidity: intramolecular excimerization of a pyrene derivative and polarization of diphenylhexatriene.

Fluorescence polarization studies of 1,6-diphenyl-1,3,5-hexatriene (DPH) have been compared with the excimer/monomer fluorescence intensity ratio (I'/I) of 1,3-di(2-pyrenyl)propane, (2Py(3)2Py). This ratio permits evaluation of changes in fluidity of the outer regions of the bilayer, where 2Py(3)2Py preferentially distributes. On the other hand, fluorescence polarization of DPH reports the structural order of the bilayer core. In the fluid phase of DMPC bilayers, for lindane concentrations higher than 25 microM, the excimer/monomer fluorescence intensity ratio (I'/I) decreases, thus reflecting an order increase of the probe environment. However, in the same conditions, the fluorescence polarization of DPH is almost insensitive to any perturbation. Identical results have been obtained in other pure lipid bilayers, namely DPPC and DSPC. However, both probes detect disordering effects of lindane in the gel phase of these lipids. The pyrene probe, unlike DPH, is very sensitive to the pretransitions of DPPC and DSPC, removed in the presence of lindane. Both probes fail to detect any apparent effect of lindane in DMPC bilayers enriched with high cholesterol content (greater than 30 mol%). However, in DMPC bilayers with low cholesterol content (less than 30 mol%), for temperatures below the phase transition of DMPC, both probes detect fluidizing effects induced by lindane. Nevertheless, above the phase transition of DMPC, 2Py(3)2Py detects ordering effects of lindane, whereas DPH detects hardly any effect. These results in DMPC bilayers with low cholesterol content are qualitatively similar to those described for DMPC without cholesterol.     

Distance measurements using paramagnetic ion-induced relaxation in the saturation transfer electron spin resonance of spin-labeled biomolecules: Application to phospholipid bilayers and interdigitated gel phases

The saturation transfer electron spin resonance (STESR) spectra of spin-labeled phosphatidylcholines in gel phase lipid bilayers are shown to be sensitive to dipolar spin-spin interactions with paramagnetic ions in the aqueous phase. The reciprocal integrated intensity of the STESR spectrum is linearly dependent on aqueous Ni²⁺ ion concentration, hence, confirming the expectation that the STESR intensity is directly proportional to the spin-lattice relaxation time of the spin label. The gradient of the relaxation rate with respect to Ni²⁺ ion concentration decreases strongly with the position of the nitroxide group down the sn-2 chain of the spin-labeled lipid and is consistent with a 1/R³ dependence on the distance, R, from the bilayer surface. The values derived for the dimensions of the bilayer and lipid molecules in the case of dipalmitoyl phosphatidylcholine (DPPC) are in good agreement with those available from x-ray diffraction studies. Allowance for the multibilayer nature of the DPPC dispersions gives an estimate of the water layer thickness that is also consistent with results from x-ray diffraction. The profile of the paramagnetic ion-induced relaxation is drastically changed with DPPC dispersions in glycerol for which the lipid chains are known to be interdigitated in the gel phase. The terminal methyl groups of the lipid chains are located approximately in register with the C-3 atoms of the sn-2 chain of the oppositely oriented lipid molecules in the interdigitated phase. The thickness of the lipid layer and the effective thickness of the lipid polar group are reduced by ~40% in the interdigitated phase as compared with the bilayer phase. The calibrations of the distance dependence established by use of spin labels at defined chain positions should be applicable to STESR measurements on other biological systems.     

Lipid phase separations induced by the association of cholera toxin to phospholipid membranes containing ganglioside GM1

The interactions of cholera toxin and their isolated binding and active subunits with phospholipid bilayers containing the toxin receptor ganglioside GM1 have been studied by using high-sensitivity differential scanning calorimetry and steady-state and time-resolved fluorescence and phosphorescence spectroscopy. The results of this investigation indicate that cholera toxin associates with phospholipid bilayers containing ganglioside GM1, independent of the physical state of the membrane. In the absence of Ca2+, calorimetric scans of intact cholera toxin bound to dipalmitoylphosphatidylcholine (DPPC) large unilamellar vesicles containing ganglioside GM1 result in a broadening of the lipid phase transition peak and a slight decrease (less than 5%) in the transition enthalpy. In the presence of Ca2+ concentrations sufficient to cause ganglioside phase separation, the association of the intact toxin to the membrane results in a significant decrease of enthalpy change for the lipid transition, indicating that under these conditions the toxin molecule perturbs the hydrophobic core of the bilayer. Calorimetric scans using isolated binding subunits lacking the hydrophobic toxic subunit did not exhibit a decrease in the phospholipid transition enthalpy even in the presence of Ca2+, indicating that the binding subunits per se do not perturb the hydrophobic core of the bilayer. On the other hand, the hydrophobic A1 subunit by itself was able to reduce the phospholipid transition enthalpy when reconstituted into DPPC vesicles. These calorimetric observations were confirmed by fluorescence experiments using pyrene phospholipids.(ABSTRACT TRUNCATED AT 250 WORDS)     

NMR study of the interaction of retinoids with phospholipid bilayers

The interaction of three vitamin A derivatives or retinoids: all-trans-retinoic acid, 13-cis-retinoic acid and retinol with multilamellar phospholipid bilayers was studied using a combination of 2H- and 31P-NMR measurements. The following model membrane systems were used: (1) dipalmitoylphosphatidylcholine (DPPC) bilayers; (2) bilayers composed of a mixture of DPPC and bovine heart phosphatidylcholine (PC); (3) mixed PC/phosphatidylethanolamine (PE) bilayers. Only a weak interaction was observed between 13-cis-retinoic acid and DPPC membranes. Addition of all-trans-retinoic acid at a molar ratio of 1:2 to the lipid causes a small decrease (5 C degrees) in the gel to liquid crystalline phase-transition temperature of DPPC, a small increase in the order parameters of the lipid side-chains of single component bilayers and no measurable effect in the other lipid systems studied. Considerably larger perturbation in the lipid bilayer structure is introduced by addition of retinol which, at a molar ratio of 1:2 to the lipid, lowered the gel to liquid crystalline phase-transition temperature of DPPC by 21 C degrees and caused a decrease of order parameters of the lipid side-chains in all three lipid bilayer systems. These effects are consistent with intercalation of retinol molecules into the bilayer interior. The results for the mixed PC/PE bilayers indicate that the presence of retinol caused lateral separation of PE- and retinol-enriched regions.     

Differing modes of interaction between monomeric Aβ(1-40) peptides and model lipid membranes: an AFM study

Membrane interactions with β-amyloid peptides are implicated in the pathology of Alzheimer's disease and cholesterol has been shown to be key modulator of this interaction, yet little is known about the mechanism of this interaction. Using atomic force microscopy, we investigated the interaction of monomeric Aβ(1-40) peptides with planar mica-supported bilayers composed of DOPC and DPPC containing varying concentrations of cholesterol. We show that below the bilayer melting temperature, Aβ monomers adsorb to, and assemble on, the surface of DPPC bilayers to form layers that grow laterally and normal to the bilayer plane. Above the bilayer melting temperature, we observe protofibril formation. In contrast, in DOPC bilayers, Aβ monomers exhibit a detergent-like action, forming defects in the bilayer structure. The kinetics of both modes of interaction significantly increases with increasing membrane cholesterol content. We conclude that the mode and rate of the interaction of Aβ monomers with lipid bilayers are strongly dependent on lipid composition, phase state and cholesterol content.     

Structure of Sphingomyelin Bilayers: A Simulation Study

We have carried out a molecular dynamics simulation of a hydrated 18:0 sphingomyelin lipid bilayer. The bilayer contained 1600 sphingomyelin (SM) molecules, and 50,592 water molecules. After construction and initial equilibration, the simulation was run for 3.8 ns at a constant temperature of 50°C and a constant pressure of 1 atm. We present properties of the bilayer calculated from the simulation, and compare with experimental data and with properties of dipalmitoyl phosphatidylcholine (DPPC) bilayers. The SM bilayers are significantly more ordered and compact than DPPC bilayers at the same temperature. SM bilayers also exhibit significant intramolecular hydrogen bonding between phosphate ester oxygen and hydroxyl hydrogen atoms. This results in a decreased hydration in the polar region of the SM bilayer compared with DPPC. Since our simulation system is very large we have calculated the power spectrum of bilayer undulation and peristaltic modes, and we compare these data with similar calculations for DPPC bilayers. We find that the SM bilayer has significantly larger bending modulus and area compressibility compared to DPPC.     

Perturbation of DPPC bilayers by high concentrations of pulmonary surfactant protein SP-B

Deuterium (²H) NMR has been used to observe perturbation of dipalmitoylphosphatidylcholine (DPPC) bilayers by the pulmonary surfactant protein B (SP-B) at concentrations up to 17% (w/w). Previous ²H NMR studies of DPPC/dipalmitoylphosphatidylglycerol (DPPG) (7:3) bilayers containing up to 11% (w/w) SP-B and DPPC bilayers containing up to 11% (w/w) synthetic SP-B indicated a slight effect on bilayer chain order and a more substantial effect on motions that contribute to decay of quadrupole echoes obtained from bilayers of deuterated DPPC. This is consistent with the perturbation of headgroup-deuterated DPPC reported here for bilayers containing 6 and 9% (w/w) SP-B. For the higher concentrations of SP-B investigated in the present work, ²H NMR spectra of DPPC deuterated in both the headgroup and chain display a prominent narrow component consistent with fast, large amplitude reorientation of some labeled lipid. Similar spectral perturbations have been reported for bilayers in the presence of the antibiotic polypeptide nisin. The observation of large amplitude lipid reorientation at high SP-B concentration could indicate that SP-B can induce regions of high bilayer curvature and thus provides some insight into local interaction of SP-B with DPPC. Such local interactions may be relevant to the formation, in vitro and in vivo, of tubular myelin, a unique structure found in extracellular pulmonary surfactant, and to the delivery of surfactant material to films at the air–water interface.Abbreviations DPPC 1,2-dipalmitoyl-sn-glycero-3-phosphocholine - DPPG 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol - DPPC-d₆₂ 1,2-perdeuterodipalmitoyl-sn-glycero-3-phosphocholine - DPPC-d₄ 1,2-dipalmitoyl-sn-glycero-3-phospho-(, perdeutero)-choline     

Organization of lipids in sarcoplasmic reticulum membrane and Ca2+-dependent ATPase activity.

The organization of lipids in sarcoplasmic reticulum membrane was studied with a variety of stearic spin labels and a phosphatidylcholine spin label. The ESR spectra of the spin-labeled membranes consisted of two components, one due to labels in lipid bilayer structure and the other due to more immobilized labels. The relative intensity of the immobilized component increased when the lipid content of the membrane was decreased by treatment with phospholipase A [EC 3.1.1.4] and subsequent washing with bovine serum albumin. Membrane containing 30% of the intact phospholipid, i.e.0.15 mg of phospholipid per mg of protein, showed a spectrum consisting only of the immobilized component (the overall splitting ranged from 58.5 G to 60.5 G). The immobilized component was ascribed to lipids complexed with protein. The fraction of lipids in the two different organizations was determined from the ESR spectrum. The activity of the Ca2+-Mg2+ dependent ATPase [ATP phosphohydrolase, EC 3.6.1.3] was found to increase almost linearly with the lipid bilayer content in the membrane, whereas phosphoenzyme formation was almost independent of the bilayer content. This indicated that the bilayer structure is necessary for the ATPase to attain its full transport activity.