Polar Bilayer Research Articles

Near-atomic images of interfaces between twin-related lamellae in a synthetic 6H-SiC sample

Transmission Electron Microscopy (TEM) and High Resolution TEM (HRTEM) investigations were used to study a complex micro-structure of twin-related lamellae of 15R SiC polytype, in syntactic coalescence with 6H-SiC. The analysis of the local stacking microstructure by means of HRTEM revealed that the perfect structure of 15R polytype, (23)3 was locally interrupted by numerous adjoining stacking faults parallel to (0001) with stacking of the coupled (22) and (33) bilayers superimposed on the twin boundaries. HR images taken exactly across both the twin boundaries showed a zig-zag pattern (23) that switched to (32) by a twin coherent interfaces or, alternatively, a zig-zag pattern (32) which passed to (23) through an isolated (33), 6H like sequence. The selected area electron diffraction (SAED) patterns taken exactly above both the twin interfaces indicate classifying of the twin found in this study as a “Friedelian” reticular merohedric twinning. However, two indistinguishable twin operations matched the observed features: a reflection through rational plane (0001), and 180°-rotation around [0001]. Since individual Si and C atoms and even the SiC bilayer polarity could not be established from these HR images, the real twin law was deduced by taking into account that the coherent structural match at the interface could be guaranteed only by a 180°-rotation around [0001]. In order to explain the origin of the planar defects found in this sample, the growth mechanism and the influence of the low-energy stacking faults were considered.

Peptides Organized as Bilayer Membranes

A buried polar bilayer interface composed of interdigitated peptide ends and a high density of CF3COO− counterions passifying lysine amines are identified in nanotubes obtained by self-assembly of short peptides. The structure reveals distinct characteristics that differentiate peptide bilayers and lipid bilayers that can now be exploited for the construction of lipid-like nanomaterials with protein functionality.

Effect of Sonication on the Thermotropic Behavior of DODAB Vesicles Studied by Fluorescence Probe Solubilization

AbstractThe effect of sonication on fluorescence probe solubilization in cationic vesicles of dioctadecyldimethylammonium bromide (DODAB) was investigated by steady‐state fluorescence of pyrene (Py), trans‐diphenylpolyenes—diphenylbutadiene (DPB), diphenylhexatriene (DPH), and their corresponding 4,4′‐dialkyl derivatives 4B4A and 4H4A fluorescence probes. The data indicate that sonication affects the bilayer polarity, the melting temperature (Tm), and the cooperativity of the melting process due to changes in vesicle morphology. The effect of temperature on the fluorescence intensity and yielding Φf and anisotropy <r> shows that the ionizable probes 4B4A and 4H4A are solubilized close to the vesicle interfaces, whereas the non‐ionizable DPH and DPB are deeper in the bilayers. Py solubilization indicates that sonicated vesicles exhibit less densely packed bilayers.

Laurdan Spectrum Decomposition as a Tool for the Analysis of Surface Bilayer Structure and Polarity: a Study with DMPG, Peptides and Cholesterol

The highly hydrophobic fluorophore Laurdan (6-dodecanoyl-2-(dimethylaminonaphthalene)) has been widely used as a fluorescent probe to monitor lipid membranes. Actually, it monitors the structure and polarity of the bilayer surface, where its fluorescent moiety is supposed to reside. The present paper discusses the high sensitivity of Laurdan fluorescence through the decomposition of its emission spectrum into two Gaussian bands, which correspond to emissions from two different excited states, one more solvent relaxed than the other. It will be shown that the analysis of the area fraction of each band is more sensitive to bilayer structural changes than the largely used parameter called Generalized Polarization, possibly because the latter does not completely separate the fluorescence emission from the two different excited states of Laurdan. Moreover, it will be shown that this decomposition should be done with the spectrum as a function of energy, and not wavelength. Due to the presence of the two emission bands in Laurdan spectrum, fluorescence anisotropy should be measured around 480 nm, to be able to monitor the fluorescence emission from one excited state only, the solvent relaxed state. Laurdan will be used to monitor the complex structure of the anionic phospholipid DMPG (dimyristoyl phosphatidylglycerol) at different ionic strengths, and the alterations caused on gel and fluid membranes due to the interaction of cationic peptides and cholesterol. Analyzing both the emission spectrum decomposition and anisotropy it was possible to distinguish between effects on the packing and on the hydration of the lipid membrane surface. It could be clearly detected that a more potent analog of the melanotropic hormone alpha-MSH (Ac-Ser(1)-Tyr(2)-Ser(3)-Met(4)-Glu(5)-His(6)-Phe(7)-Arg(8)-Trp(9)-Gly(10)-Lys(11)-Pro(12)-Val(13)-NH(2)) was more effective in rigidifying the bilayer surface of fluid membranes than the hormone, though the hormone significantly decreases the bilayer surface hydration.

Articaine interaction with DSPC bilayer: A 13C and 31P solid-state NMR study

Articaine hydrochloride, 4-methyl-3-(2-[propylamino]propionamido)-2-thiophenecarboxylic acid, methyl ester hydrochloride, is a local anaesthetic commonly used in dentistry, and is classified as an amide local anaesthetic. Solid-state 13C and 31P NMR were used to investigate the uncharged articaine species (sample pH 10.0) when interacting with distearoylphosphatidylcholine (DSPC) model membranes. The DSPC phospholipid bilayer was studied at four different molar ratios of articaine, 10, 25, 40, and 55 mol%, respectively. The articaine concentration-dependent decrease in the DSPC bilayer gel-to-liquid-crystalline phase-transition temperature demonstrates substantial articaine interaction with this bilayer. A DSPC bilayer contains a large hydrophobic core and the 13C and 31P NMR spectra of the 40 mol% articaine-containing sample demonstrate a disturbance in the molecular packing of the polar bilayer region that extends into the hydrophobic region, evidenced by carbon 2 and 3 of the stearoyl acyl chains. Observed 31P and 13C NMR spectral changes when articaine is increased from 40 to 55 mol%, suggest formation of articaine aggregates and decrease in DSPC bilayer perturbation at the latter articaine level.

Bilayer polarity and its thermal dependency in the ℓ o and ℓ d phases of binary phosphatidylcholine/cholesterol mixtures

Diverse variations in membrane properties are observed in binary phosphatidylcholine/cholesterol mixtures. These mixtures are nonideal, displaying single or phase coexistence, depending on chemical composition and other thermodynamic parameters. When compared with pure phospholipid bilayers, there are changes in water permeability, bilayer thickness and thermomechanical properties, molecular packing and conformational freedom of phospholipid acyl chains, in internal dipolar potential and in lipid lateral diffusion. Based on the phase diagrams for DMPC/cholesterol and DPPC/cholesterol, we compare the equivalent polarity of pure bilayers with specific compositions of these mixtures, by using the Py empirical scale of polarity. Besides the contrast between pure and mixed lipid bilayers, we find that liquid-ordered (ℓ o) and liquid-disordered (ℓ d) phases display significantly different polarities. Moreover, in the ℓ o phase, the polarities of bilayers and their thermal dependences vary with the chemical composition, showing noteworthy differences for cholesterol proportions at 35, 40, and 45 mol%. At 20 °C, for DMPC/cholesterol at 35 and 45 mol%, the equivalent dielectric constants are 21.8 and 23.8, respectively. Additionally, we illustrate potential implications of polarity in various membrane-based processes and reactions, proposing that for cholesterol containing bilayers, it may also go along with the occurrence of lateral heterogeneity in biological membranes.

Articaine interaction with DSPC bilayer: a 13C and 31P solid-state NMR study

Abstract Articaine hydrochloride, 4-methyl-3-(2-[propylamino]propionamido)-2-thiophenecarboxylic acid, methyl ester hydrochloride, is a local anaesthetic commonly used in dentistry, and is classified as an amide local anaesthetic. Solid-state 13C and 31P NMR were used to investigate the uncharged articaine species (sample pH 10.0) when interacting with distearoylphosphatidylcholine (DSPC) model membranes. The DSPC phospholipid bilayer was studied at four different molar ratios of articaine, 10, 25, 40, and 55 mol%, respectively. The articaine concentration-dependent decrease in the DSPC bilayer gel-to-liquid-crystalline phase-transition temperature demonstrates substantial articaine interaction with this bilayer. A DSPC bilayer contains a large hydrophobic core and the 13C and 31P NMR spectra of the 40 mol% articaine-containing sample demonstrate a disturbance in the molecular packing of the polar bilayer region that extends into the hydrophobic region, evidenced by carbon 2 and 3 of the stearoyl acyl chains. Observed 31P and 13C NMR spectral changes when articaine is increased from 40 to 55 mol%, suggest formation of articaine aggregates and decrease in DSPC bilayer perturbation at the latter articaine level.

An attempt to determine the polarity of bilayer of cationic and anionic surfactants vesicle: A chemical probe technique study

As core part of vesicle, the polarity of bilayer plays a key role on the stability and rigidness of the aggregate. In this paper, a novel chemical probe technique was successfully established to determine the polarity of the bilayer of the vesicle which was prepared from cationic and anionic surfactants with single chain, respectively. The thickness of bilayer of vesicle is only approximately 4 nm, therefore, the small size singlet oxygen with a long lifetime produced from dye-photosensitized oxidation has ability and sufficient time to diffuse out of the bilayer to react with the substrate incorporated in another vesicle's bilayer. The results show that the distribution ratio of the photooxidation products is related to the polarity of reaction medium and thus it can be used as a probe to determine the polarity of bilayer of the vesicle.

A New Fluorescent Squaraine Probe for the Measurement of Membrane Polarity

The present study was undertaken to evaluate the sensitivity of newly synthesized squaraine dye 1 to the changes in lipid bilayer physical properties and compared it with the well-known dye 2. Partitioning of the dye 1 into lipid bilayer was found to be followed by significant increase of its fluorescence intensity and red-shift of emission maximum, while intensity of the dye 2 fluorescence increased only slightly on going from aqueous to lipidic environment. This suggests that dye 1 is more sensitive to the changes in membrane properties as compared to dye 2. Partition coefficients of the dye 1 have been determined for the model membranes composed of zwitterionic phospholipid phosphatidylcholine (PC) and its mixtures with positively charged detergent cetyltrimethylammonium bromide (CTAB), anionic phospholipid cardiolipin (CL), and sterol (Chol). The spectral responses of the dye 1 in different liposome media proved to correlate with the increase of bilayer polarity induced by Chol and CL or its decrease caused by CTAB. It was concluded that dye 1 can be used as fluorescent probe for examining membrane-related processes.

Red Cell Membrane Lipid Changes at 3500 m and on Return to Sea Level

Previous studies have shown that acute hypobaric hypoxia, obtained in a hypobaric chamber, and subsequent reoxygenation, give rise to modifications of the erythrocyte membrane lipid dynamics, resulting in an increased lateral diffusivity of the membrane lipids, and this was interpreted as the result of a modified lipid-protein interaction. The aim of the present study was to determine the effect of the reoxygenation condition in individuals after 3 days at an altitude of 3,500 m above sea level. Reoxygenation was a consequence of returning to sea level. Resting blood samples from both conditions were obtained, and erythrocytes were separated and immediately lysed for membrane isolation. We measured the bilayer polarity in membranes with Laurdan, a fluorescent probe. We also measured malondialdehyde in membrane lipids, an indicator of oxidative damage. We found a 12% (p = 0.016, n = 7) increase in the polarity of the membrane bilayer surface, and an increase of 70% (p = 0.005, n = 7) in the formation of malondialdehyde in the membrane after the reoxygenation condition. The membrane bilayer polarity increase is due to an oxidative modification of the phospholipid backbone after reoxygenation. People working and/or recreating at moderate altitude (3,500 m) may be at risk of erythrocyte membrane oxidative damage upon returning to sea level, and therefore a better understanding of the processes occurring upon reoxygenation may lead to proposed strategies to minimize this effect.

The Polar Nature of 7-Ketocholesterol Determines Its Location within Membrane Domains and the Kinetics of Membrane Microsolubilization by Apolipoprotein A-I

7-Ketocholesterol is an oxidized derivative of cholesterol with numerous physiological effects. In model membranes, 7-ketocholesterol and cholesterol were compared by physical measures of bilayer order and polarity, formation of detergent resistant domains (DRM), phase separation, and membrane microsolubilization by apolipoprotein A-I. In binary mixtures of a saturated phosphatidylcholine (PC), dipalmitoyl-PC (DPPC), and cholesterol or 7-ketocholesterol, the sterols modulate bilayer order and polarity and induce DRM formation to a similar extent. Cholesterol induces formation of ordered lipid domains (rafts) in tertiary mixtures with dioleoyl-PC (DOPC) and DPPC, or DOPC and sphingomyelin (SM). In tertiary mixtures, cholesterol increased lipid order and reduces bilayer polarity more than 7-ketocholesterol. This effect was more pronounced when the mixtures were in a miscible liquid-disordered (L(d)) phase. Substitution of 7-ketocholesterol for cholesterol dramatically reduced the extent of DRM formation in DOPC/DPPC and DOPC/SM bilayers and ordered lipid phase separation in mixtures of a spin-labeled PC with DPPC and with SM. Compared to cholesterol, 7-ketocholesterol decreased the rate for the microsolubilization of dimyristoyl-PC multilamellar vesicles by apolipoprotein A-I. The membrane effects of 7-ketocholesterol were dependent on the phospholipid matrix. In L(d) phase phospholipids, a model for 7-ketocholesterol indicates that the proximity of the 7-keto and 3beta-OH groups puts both polar moieties at the lipid-water interface to tilt the sterol nucleus to the plane of the bilayer. 7-Ketocholesterol was less effective in forming ordered lipid domains, in decreasing the level of bilayer hydration, and in forming phase boundary bilayer defects. Compared to cholesterol, 7-ketocholesterol can differentially modulate membrane properties involved in protein-membrane association and function.

Crystal structure of (3S,1'S)-2,2-dimethyl-3-[1,2-cyclohexylidenedioxyethyl]- tetrahydro-1,2-oxazolium tetrafluoroborate, (C13H24NO3)[BF4

C13H24BF4NO3, orthorhombic, C222i (no. 20), a = 9.320(2) A, b = 10.6761(8) A, c = 33.786(2) A, V= 3361.6 A, Z = 8, Rgi(F) = 0.064, wR^F) = 0.185,7= 293 K. Source of material The title compound has been obtained by 1,3-dipolar cycloaddition of ethylene and the nitrile oxide obtained in situ from hydroximoyl chloride, derived from 2,3-O-cyclohexylidene-Dglyceraldehyde [1-3]. This was followed by N-methylation of the intermediate isoxazoline with trimethyloxonium tetrafluoroborate and reduction on treatment with sodium borohydride in ethanol [2]. Further methylation of the corresponding major isoxazolidine isomer (separated by MPLC, ratio of diastereoisomers = 84:16) with trimethyloxonium tetrafluoroborate [3-5] and recrystallization from ethanol afforded the isoxazolidinium salt in the form of colorless crystals (m.p. 443-444 Κ, αο = -29.4°, c = 0.81, CH2CI2). Discussion The isoxazolidine ring system shows an envelope conformation (figure, top). Three atoms (C10,CI 1,C12) of thecyclohexylidene moiety exhibit very large displacement parameters. A resolution of eventual disorder via split positions was not performed, the distances of the C-C bonds deviate less than 5 % from normal values. The fluorine atoms of the tetrafluoroborate anion have also large displacement parameters, which indicates considerable rotation of the anion. The packing diagram reveals a bilayer-type stacking of the molecules with alternating polarity along the c axis (figure, bottom). The non-polar bilayer is built up by a face-to-face orientation of the cyclohexylidene moieties; the polar bilayer is built by the hetero atoms of the isoxazolidines and the tetrafluoroborate anions. Table 1. Data collection and handling. Crystal: Wavelength: μ· Diffractometer, scan mode: 2βηωχ: N(hkl)masimd, N(hklhm^ Criterion for / 2 o(ldta), 1174 199 SHELXS-97 [6], SHELXL-97 [7] Table 2. Atomic coordinates and displacement parameters (in A). Correspondence author (e-mail: jager.ioc@po.uni-stuttgart.de) Atom Site X y ζ Um, H(1A) 8c 0.0618 0.5178 0.4513 0.146 H(1B) 8c -0.1065 0.5198 0.4543 0.146 H(2A) 8c 0.0584 0.4363 0.3923 0.120 H(2B) 8c -0.1006 0.4873 0.3909 0.120 H(3) 8c -0.1956 0.3044 0.4095 0.082 H(4) 8c -0.0728 0.1290 0.3796 0.083 H(5A) 8c -0.2387 0.1880 0.3358 0.102 H(5B) 8c -0.1904 0.3296 0.3366 0.102

Lipid Bilayer Topology of the Transmembrane α-Helix of M13 Major Coat Protein and Bilayer Polarity Profile by Site-Directed Fluorescence Spectroscopy

This article presents a new formalism to perform a quantitative fluorescence analysis using the Stokes shift of AEDANS-labeled cysteine mutants of M13 major coat protein incorporated in lipid bilayers. This site-directed fluorescence spectroscopy approach enables us to obtain the topology of the bilayer-embedded transmembrane α-helix from the orientation and tilt angles, and relative bilayer location. Both in pure dioleoylphosphatidylcholine and dioleoylphosphatidylcholine/dioleoylphosphatidylglycerol (4:1 mol/mol) bilayers, which have a similar bilayer thickness, the tilt angle of the transmembrane helix of the coat protein turns out to be 23° ± 4. Upon decreasing the hydrophobic thickness on going from dieicosenoylphosphatidylcholine to dimyristoylphosphatidylcholine, the tilt angle and orientation angle of the transmembrane α-helix change. The protein responds to an increase of hydrophobic stress by increasing the tilt angle so as to keep much of its hydrophobic part inside the bilayer. At the same time, the transmembrane helix rotates at its long axis so as to optimize the hydrophobic and electrostatic interactions of the C-terminal phenylalanines and lysines, respectively. The increase of tilt angle cannot completely keep the hydrophobic protein section within the bilayer, but the C-terminal part remains anchored at the acyl-chain/glycerol backbone interface at the cost of the N-terminal section. In addition, our analysis results in the profile of the dielectric constant of the hydrophobic domain of the bilayer. For all phospholipid bilayers studied the profile has a concave shape, with a value of the dielectric constant of 4.0 in the center of the bilayer. The dielectric constant increases on approaching the headgroup region with a value of 12.4 at the acyl-chain/glycerol backbone interface for the various phosphatidylcholines with different chain lengths. For dioleoylphosphatidylcholine/dioleoylphosphatidylglycerol (4:1 mol/mol) bilayers the value of the dielectric constant at the acyl-chain/glycerol backbone interface is 18.6. In conclusion, the consistency of our analysis shows that the applied cysteine-scanning mutagenesis method with AEDANS labeling of a helical transmembrane protein in combination with a quantitative formalism offers a reliable description of the lipid bilayer topology of the protein and bilayer properties. This also indicates that the spacer link between the protein and AEDANS label is long enough to monitor the local polarity of the lipid environment and not that of the amino-acid residues of the protein, and short enough to have the topology of the protein imposing on the fluorescence properties of the AEDANS label.

Idiopathic infertility: susceptibility of spermatozoa to in-vitro capacitation, in the presence and the absence of palmitylethanolamide (a homologue of anandamide), is strongly correlated with membrane polarity studied by Laurdan fluorescence.

Capacitation is a widely investigated process, which induces sperm plasma membrane changes resulting in its increased affinity for the zona pellucida. The fluorescent probe Laurdan, localized only within the plasma membrane of spermatozoa, is particularly useful to evaluate bilayer polarity in this part of the cell. According to a previous study, sperm membranes from oligozoospermic and some normozoospermic subjects (defined according to World Health Organization criteria), are characterized by low polarity (high Laurdan exGP(340)), while the spermatozoa from the remaining normozoospermic men show a larger polarity (low exGP(340)). In this paper, Laurdan was used to study membrane changes occurring during in-vitro capacitation, on sperm membranes from oligozoospermic and normozoospermic subjects. Results indicated that cells with high exGP(340) show a different susceptibility to Ca(2+)-induced capacitation in vitro, as compared with cells with low exGP(340). Palmitylethanolamide, physiologically present in human reproductive tracts, affects the time-course of in-vitro capacitation, increasing the rate of this process only in the cells with a lower membrane polarity.

Definition of the specific roles of lysolecithin and palmitic acid in altering the susceptibility of dipalmitoylphosphatidylcholine bilayers to phospholipase A2.

Bilayers composed of phosphatidylcholine initially resist catalysis by phospholipase A2. However, after a latency period, they become susceptible when sufficient reaction products (lysolecithin and fatty acid) accumulate in the membrane. Temperature near the main bilayer phase transition and calcium concentration modulate the effectiveness of the reaction products. The purpose of this study was to examine the individual contributions of lysolecithin and palmitic acid to the susceptibility of dipalmitoylphosphatidylcholine vesicles and to rationalize the effects of temperature and calcium. Various fluorescent probes (Prodan, Laurdan, pyrene-labeled fatty acid, and dansyl-labeled phospholipid) were used to assess changes in the ability of the reaction products to perturb the bilayer and to affect the interactions with the enzyme. Un-ionized palmitic acid decreased bilayer polarity and perturbed the membrane surface exposing some of the Prodan to bulk water. Lysolecithin increased bilayer polarity and the rate of dipolar relaxation in response to the excited states of Laurdan and Prodan. A combination of the individual contributions of each product was observed when palmitic acid and lysolecithin were present together at low calcium, and the effects of lysolecithin dominated at high calcium. Palmitic acid, but not lysolecithin, promoted the binding of phospholipase A2 to the bilayer surface in the absence of calcium. Lysolecithin reduced the ability of fatty acid to enhance binding apparently by altering the structure of fatty acid domains in the membrane. Furthermore, increased temperature and ionization of the fatty acid tended to cause segregation of bound phospholipase A2 into domains poor in phospholipid content which presumably impeded bilayer hydrolysis. In contrast, un-ionized palmitic acid and lysolecithin promoted hydrolysis by augmenting a step distal to the adsorption of enzyme to the bilayer. This kinetic response to lysolecithin was calcium-dependent. A model accounting for these varied influences of the reaction products is presented.

Interactions of thionin from Pyrularia pubera with dipalmitoylphosphatidylglycerol large unilamellar vesicles.

The peptide toxin thionin from Pyrularia pubera binds to dipalmitoylphosphatidylglycerol (DPPG) large unilamellar vesicles as shown by an increase in the intensity and blue-shift of the fluorescence emission spectrum of the single tryptophan residue of the protein. The magnitude of these fluorescence changes increased with temperature near the thermotropic phase transition of DPPG (about 40 degrees C). Fluorescent probes sensitive to the structure and dynamics of the membrane were used to assess the effect of thionin binding on bilayer properties. The fluorescence emission spectra of Prodan, Patman, and Laurdan all showed spectral changes consistent with an increase in bilayer polarity at temperatures below the DPPG phase transition but a decrease in polarity at higher temperatures. Fluorescence polarization experiments and the ratio of monomer-to-excimer fluorescence of the probe 1,3-bis(1-pyrene)propane suggested that thionin increases the bilayer order above the transition temperature. Differential scanning calorimetry revealed that thionin broadens the transition and either increases or decreases the melting temperature depending on the concentration of the peptide. Taken together, the data are consistent with at least three distinct interactions of thionin with the bilayer: (1) thionin bound electrostatically to the bilayer surface; (2) tryptophan of the bound thionin inserted into the bilayer; (3) high-order aggregates of thionin-bound vesicles.

Membrane oxidative damage induced by ionizing radiation detected by fluorescence polarization.

Effects of ionizing radiation on biological membranes include alterations in membrane proteins, peroxidation of unsaturated lipids accompanied by perturbations of the lipid bilayer polarity. We have measured radiation-induced membrane modifications using two fluorescent lipophilic membrane probes (TMA-DPH and DPH) by the technique of fluorescence polarization on two different cell lines (Chinese hamster ovary CHO-K1 and lymphoblastic RPMI 1788 cell lines). gamma-Irradiation was performed using a 60Co source with dose rates of 0.1 and 1 Gy/min for final doses of 4 and 8 Gy. Irradiation induced a decrease of fluorescence intensity and anisotropy of DPH and TMA-DPH in both cell lines, which was dose-dependent but varied inversely with the dose rate. Moreover, the fluorescence anisotropy measured in lymphoblastic cells using TMA-DPH was found to decrease as early as 1 h after irradiation, and remained significantly lower 24 h after irradiation. This study indicates that some alterations of membrane fluidity are observed after low irradiation doses and for some time thereafter. The changes in membrane fluidity might reflect oxidative damage, thus confirming a radiation-induced fluidization of biological membranes. The use of membrane fluidity changes as a potential biological indicator of radiation injury is discussed.

Erythrocyte membrane barrier function: role of bilayer polarity and skeletal proteins.

Conference Article| November 01 1992 Erythrocyte membrane barrier function: role of bilayer polarity and skeletal proteins Bernhard Deuticke; Bernhard Deuticke * 1Institut für Physiologie, Rheinisch-Westfälische Technische Hochschule, D-5100 Aachen, Germany *Prof. Dr. B. Deuticke, Institut für Physiologie, Klinikum, Pauwelsstr. 30, D-5100 Aachen, Germany Search for other works by this author on: This Site PubMed Google Scholar Sabine Klonk; Sabine Klonk 1Institut für Physiologie, Rheinisch-Westfälische Technische Hochschule, D-5100 Aachen, Germany Search for other works by this author on: This Site PubMed Google Scholar Cees W. M. Haest Cees W. M. Haest 1Institut für Physiologie, Rheinisch-Westfälische Technische Hochschule, D-5100 Aachen, Germany Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1992) 20 (4): 769–773. https://doi.org/10.1042/bst0200769 Article history Received: July 14 1992 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation Bernhard Deuticke, Sabine Klonk, Cees W. M. Haest; Erythrocyte membrane barrier function: role of bilayer polarity and skeletal proteins. Biochem Soc Trans 1 November 1992; 20 (4): 769–773. doi: https://doi.org/10.1042/bst0200769 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search Keywords: DTE, dithioerythritol, NEM, N-ethylmaleimide, MTPP+, methyltriphenylphosphonium ion This content is only available as a PDF. © 1992 Biochemical Society1992 Article PDF first page preview Close Modal You do not currently have access to this content.

On coenzyme Q orientation in membranes: A linear dichroism study of ubiquinones in a model bilayer

A general approach is developed to interpret linear dichroism (LD) spectra of ubiquinones (Qn) in host bilayers. Information is reported in terms of guest-host mutual orientation and localization. The overall orientational anisotropy of guest ubiquinone molecules is described by a basic set of limiting orientation/localization modes. Assignments of the UV transitions of the ubiquinone chromophore were obtained by the liquid crystal-linear dichroism technique and molecular orbital (CNDO/S) calculations. The LD spectra of Qn in the bilayers provided by the lyotropic nematic mesophase exhibited by water solutions of potassium laurate and decanol were interpreted on the basis of the above assignments. The resulting experimental evidence showed a multisite distribution in the host bilayer for the aromatic heads of all the investigated Qn derivatives except Q0. The orientational distribution suggested by the LD spectra fits the solubilization model recently proposed by G. Lenaz [J. Membrane Biol. (1988) 104:193-209] for ubiquinone in lipid membranes. Within this model Qn molecules are located in the midplane and their headgroups oscillate transversally across the membrane. Q0 instead has a single site location, close to the polar bilayer interface. Experimental evidence that the headgroup carbonyls tend to grasp the polar interface of the host bilayer was also obtained. Orientation and location distributions of Qn guest molecules are therefore likely to result from the tendency of their aromatic heads to grasp the polar heads of the host bilayer and from the concurrent tendency of their chains to settle into the hydrocarbon host interior.

The orientation of (−)- Δ9-tetrahydrocannabinol in DPPC bilayers as determined from solid-state 2H-NMR

The orientation of the motional axis of (−)- Δ 9-tetrahydrocannabinol in dipalmitoylphosphatidylcholine model membrane was calculated from the 2H quadrupolar splittings ( Δν Q) of individual deuterons strategically located on the cannabinoid tricyclic component. The molecule assumes an orientation in which its long axis is nearly perpendicular to the phospholipid chains and its most ordered axis is almost in the plane of the aromatic ring. This ‘awkward’ cannabinoid orientation in the membrane presumably occurs in order to allow the phenolic hydroxyl group to direct itself towards the polar bilayer interface.