Lipid Bilayer Phase Research Articles

The influence of the lipid bilayer phase state on the p-aminohippurate (PAH) transport and the activity of the alkaline phosphatase in brush-border membrane vesicles from normal and mutant rats

The kinetic parameters of p-aminohippurate transport and activity of the alkaline phosphatase were studied using brush-border membrane vesicles isolated from the kidney cortex of normal and mutant (strain of Campbell) rats. p-Aminohippurate (PAH) transport of both normal and mutant animals was carried out by the mechanism of facilitated diffusion. The apparent Michaelis constant at 36 degrees C was equal to 7 mM, the maximal rate of PAH transport was 15 nmol/min per mg protein and the constant of inhibition by probenecid was 0.5 mM for normal rats and, respectively, 29 mM, 62 nmol/min per mg protein and 1.4 mM for mutant rats. The Arrhenius plot for the PAH transport and activity of the alkaline phosphatase showed the breakpoints at 28-30 degrees C for normal rats and at 36-38 degrees C for the Campbell strain rats. The thermotropic phase transitions detected by the EPR method with 5-doxylstearate as a probe were recorded at 21-30 degrees C and 30-35 degrees C for normal and mutant rats, respectively. Therefore, characteristic features of the PAH carrier and alkaline phosphatase activity in normal and Campbell strain rats are determined by the difference in the phase state of their membrane lipid bilayers. We suppose that mutation in the Campbell strain gives rise to a membrane pleiotropic effect which enables us to understand the mechanism of genetic control of the lipid structure and membrane fluidity.

Reversible Association of Porphyrin Derivative Incorporated into Hydrophobic Region of Phospholipid Bilayer

3,8,13,17-Tetramethyl-7,12-divinyl-2,18-bis-(18-hydroxyoctadecyloxycarbonyl-ethyl)porphinato zinc (BHPZn) was incorporated into the hydrophobic bilayer membrane region of liposome of dipalmitoyl phosphatidylcholine (DPPC). Thionine was added to the outer aqueous phase of the liposome suspension. Fluorescence spectra were measured to check the influence of phase of lipid bilayer on the energy transfer from BHPZn to thionine. At temperatures below the phase transition temperature (Tc) of DPPC liposome, BHPZn was assembled in the bilayer membrane and the excitation energy of BHPZn was dissipated by the static self-concentration quenching. The energy transfer efficiency to thionine was considerably low. Against this, at temperatures above the Tc, concentrated BHPZn was dispersed uniformly and reduced the self-quenching of BHPZn in the excited state. The energy transfer efficiency from porphyrin to thionine increased with heating depending on the fluidity of the lipid bilayer. The fluorescence characteristics of BHPZn reflected the phase behavior of the lipid bilayer, and was simply controlled by changing the physicochemical feature of lipids such as fluidity.

Liposome—glass interaction. Influence of the lipid bilayer phase state

The adsorption of dipalmitoylphosphatidylcholine (DPPC) and palmitic acid from multilamellar lipid dispersions in excess water onto hydrophilic and hydrophobic glass surfaces was studied. Adsorption isotherms at different temperatures were obtained. The adsorbed lipid amount at saturation, Γ ∞, was found to depend strongly on the phase state of the lipid dispersion. For DPPC, a sharp decrease of Γ ∞ was observed at the gel—liquid crystal phase transition at 41 °C (P β′-L α). The DPPC adsorption from the gel phases L β′ and P β′ was significantly greater than that from the low-temperature crystalline L c phase. The L c-isotropic phase transition of palmitic acid was also clearly reflected in the temperature dependence of Γ ∞ for this lipid. Electron microscopy yielded direct evidence for the presence of lipid aggregates and restructured liposomes on the glass surface. In combination with the adsorption data, this shows that fluid liposomes bind less to glass surfaces than solid liposomes.

Electrical properties of a purified complex of α-latrotoxin and its receptor incorporated into planar lipid bilayers

Membrane reconstitution experiments have been performed using artificial membranes of soybean lecithin in order to determine the physiological role played in the neuronal membrane by α-LTx binding protein, recently purified from solubilized bovine synaptosomal membranes. When unilamellar liposomes (with and without the reconstituted receptor, which had been preincubated with α-Latrotoxin) were added to the aqueous phase of a planar lipid bilayer, they induced a stepwise increase in conductance. The effects of α-LTx on the receptor-bearing membranes were compared with those induced by the toxin in the control membranes. For the receptor-bearing membranes, the mean latent period preceding the appearance of the toxin-induced channels was considerably shorter, and macroscopic currents were fifty times larger at lower concentrations of α-Latrotoxin. In addition, there was a change in the voltage dependence of the current, and the appearance of conductance steps at positive voltages was observed. These results suggest that the role of the receptor is twofold: it facilites the transmembrane insertion of the toxin, and modulates the properties of the resulting channels.

Magic Numbers of Water Molecules Bound Between Lipid Bilayers

Phospholipids are the essential components of biological membranes. Depending on both temperature and amount of water, a single lipid species displays various liquid crystalline structures, namely different types of bilayers seperated by well-defined water layers. Recent investigations have revealed that the number of these inter-bilayer water molecules controls the dynamics and the structure of the lipid bilayer phases. For instance, the number of water molecules bound per lipid molecule changes discontinuously at the various structural phase transitions of a lipid-water system. Each phase is characterized by a magic number of bound water molecules.On the other hand, the dynamics of the bilayers as the rotational motion of the lipid head group or as the trans-gauche isomerization rate of the lipid chains depend on the number of inter-bilayer water molecules. Properties of bound water as well as the inter-bilayer forces are discussed. The magic numbers are expected to be the result of the competition between the attractive van der Waals force of two adjacent lipid bilayers and the repulsive force due to the inter-bilayer bound water molecules.

Paramagnetic probes in membrane biophysics

The use of paramagnetic probes in membrane research is reviewed. Electron paramagnetic resonance studies on model and biological membranes doped with covalent and non-covalent spin-labels have been discussed with special emphasis on the methodology and the type of information obtainable on several important phenomena like membrane fluidity, lipid flip-flop, lateral diffusion of lipids, lipid phase separation, lipid bilayer phase transitions, lipid-protein interactions and membrane permeability. Nuclear magnetic resonance spectroscopy has also been effectively used to study the conformations of cation mediators across membranes and to analyse in detail the transmembrane ionic motions at the mechanistic level.

Photon correlation spectroscopy as a probe of planar lipid bilayer phase transitions.

Photon correlation spectroscopy has been applied to study phase transitions of planar bilayer membranes. The membrane tension and one specific membrane viscosity are probed. Difficulties arising in the measurement of the temperature dependence of these properties are discussed and a servo-control system to overcome them is described. Typical data are presented for monoglyceride bilayers. Membranes incorporating cholesterol display effects below the lipid transition temperature which are interpreted in terms of separation within the membrane into cholesterol-rich fluid regions and regions of lipid in the gel phase. Some of the cholesterol-rich regions are apparently of macroscopic extent.

Evidence for Weak First-Order Nature of Lipid Bilayer Phase Transition from the Analysis of Pseudo-Critical Specific Heat

The specific heat of aqueous suspension of dipalmitoylphosphatidylcholine obtained by ac calorimetry is analyzed by the least-squares fit under certain assumptions about the functional form for critical phenomena. Based upon the theory on the critical or pseudo-critical behavior, a weak first-order phase transition is proposed from the fact that a most probable solution follows that pseudo-critical behavior takes place, i.e., α=α'=0.5, the temperature difference between the spinodal points is as small as 0.24 K and the thermal hysteresis at the main transition is smaller than 0.2 K.

Specific deuteration and membrane structures.

Diffraction methods have provided a firm time-averaged picture of lipid bilayers and membranes. The basic characteristics of lipid bilayer phases have been obtained, mainly by x-ray diffraction, and some overall mean conformational properties of lipids have been determined (6, 10, 11, 13, 19, 20). As outlined by Tardieu et al. (20), one remarkable feature of lipids is their ability to combine in one phase a periodically ordered long-range organization in one, two, or three dimensions and a highly disordered short-range conformation. This property seems closely related to the function of the lipid matrix in natural membranes. In particular, because of this short-range disorder, it was not possible for a long time to determine the mean conformation of a lipid in a bilayer at higher resolution. Every segment undergoes large positional fluctuations, so that x-ray profiles can give only the superposition of these overlapping segmental distributions, thus hiding the details of the average lipid conformation.

Theoretical conformational analysis of phospholipids: I. Study of the interactions between phospholipid molecules by use of semi-empirical methods with the explicit introduction of polar headgroup interactions

We present a theoretical conformational analysis of a system composed of seven dipalmitoylphosphatidylethanolamine molecules in interaction. The combined use of classical semi-empirical methods for the polar headgroup region with mechanical statistical calculations for the aliphatic chains permits the evaluation of the free energy for a phospholipids molecule. The free energy variation in function of the mean intermolecular interchain distance gives information about the main lipid bilayer phase transition. It appears, however, necessary to take into account the hydration of the polar headgroups.

A theoretical study of lipid-protein interactions in bilayers

We present a theoretical study of the effect of different types of lipid-protein interactions on the thermodynamic properties of protein-containing lipid bilayers. The basis of this work is a theoretical model for pure lipid bilayer phase transitions developed earlier by Scott. Simple assumptions on the nature of the lipid conformations near a protein strongly affect the predicted properties of the model. Here we consider (a) random protein-lipid contacts, (b) enhanced contact between protein and lipid with a number of gauche bonds, and (c) enhanced contact between protein and all-trans but tilted lipid chains. Comparison of predicted results with experimental data seems to favor point c above but, by itself point c does not work well at larger protein concentrations. The results are discussed in the light of spectroscopic data, lipid-protein (plus annular lipid) miscibility, and interprotein forces.

2H- and 31P-NMR studies of bilayers composed of 1-acyllysophosphatidylcholine and fatty acids

1-Palmitoyllysophosphatidylcholine has been mixed in equimolar amounts with specifically deuterated palmitic acid and the structural properties of the lipid/water phase have been studied by 2H- and 31P-nuclear magnetic resonance. The order profile of the free palmitic acid is very similar to that of the parent compound 1,2- dipalmitoyl-sn- glycero-3-phosphocholine at temperatures above the gel-to-liquid crystal phase transition. The bending of the sn-2 chain which is typical for diacyl lipids is not observed for the free palmitic acid. The mixture of lysolipid and palmitic acid exhibits well-defined quadrupole splittings even at temperatures below the gel-to-liquid crystal phase transition. Hence it is possible for the first time to establish an order profile in the gel-state of the lipid bilayer phase. Between carbon atoms 5 to 12 the palmitic acid chain is found to assume the extended all- trans conformation with a very small contribution from gauche defects. Towards the methyl terminal a distinct increase in the gauche probability can be noted. The motion of the phosphocholine headgroup was also studied by 2H- and 31P-NMR using selectively deuterated 1-palmitoyllysophosphatidylcholine. The headgroup has a considerably larger motional freedom in the mixture of lysolipid and palmitic acid than in 1,2- dipalmitoyl-sn- glycero-3-phosphocholine . In addition, the average headgroup conformations are also different in the two systems.

ChemInform Abstract: NONPLANAR CONFORMERS AND THE PHASE BEHAVIOR OF SOLID N‐ALKANES

Solidsolid phase transitions of the odd n-alkanes n-C17H36 through n-C29H60 were studied by using differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Two phase transitions were found in C25, C2,, and C29 in addition to the previously reported highest-temperature solid-solid transition (the so-called rotator transition). IR spectra revealed that, as the temperature is raised, the concentration of nonplanar conformers successively increases through each phase transition. Three types of nonplanar have been identified in the highest-temperature phase of all the n-alkanes: (gt ...), kink (...gtg'...), and (...gg...). The end-gauche defect was observed in the lower-temperature phases as well. Kink conformers, however, were observed only in the highest-temperature phase while double-gauche were found in measurable concentrations only within a few degrees of the melting point. The concentrations of nonplanar conformers in the highest-temperature phases increase with increasing chain length. For example, roughly 70% of C29 molcules are nonplanar prior to melting, in contrast to 5-10% for C17. The relationship between the existence of nonplanar conformers and the various distinct solid phases presents a major puzzle. Normal alkanes undergo a remarkable series of solidsolid phase transitions prior to melting. Analogous premelting transitions are also found in a number of more complex systems which contain hydrocarbon chains as major constituents. These systems include polyethylene,' variously substituted alkanes,2 and biological ~nembranes.~ In the latter cases, the phase changes are believed to be intimately related to the state of the hydrocarbon component. For example, current models of the lipid bilayer phase transitions require detailed consideration of the changes in conformation of the alkane chains4 Since the n-alkanes themselves are the sim- plest of these chain-molecule solids, they are a natural starting point for understanding the premelting transitions exhibited by all of these systems. The phase behavior of even the n-alkanes is complex. All odd n-alkanes between C9 and C45 undergo at least one premelting phase transition, and the longer members show no less than four high-temperature solid phases in addition to the low-temperature crystalline phases5 The nature of these phases is not well un- derstood although it is clear that the higher-temperature phases involve increasing degrees of disorder. By here we mean any deviation from the regular arrangement of all-trans chains found in the low-temperature solid. In this paper we focus mainly on one aspect of the disordering processes occurring in these solids-that involving conformational changes. We show that infrared spectroscopy is sensitive to the presence of various nonplanar (not all-trans) conformers and to some types of intermolecular order. We will find that disorder occurs in a series of apparently solid phases. The question then arises how can the apparent short-range implied by these nonplanar conformations be reconciled with the existence of a series of phases showing long-range order? This question which is fundamental to the understanding of the more complex systems such as biolipid bilayers will be taken up again in the Conclusion. The body of this paper presents the infrared spectra of the alkanes as a function of temperature with an analysis of the conformational defects seen in the various phases.

The conformation of hydrocarbon chains in disordered layer systems

A Monte Carlo computer model of a monolayer of n-hexadecane molecules has been built at a surface density corresponding to 0.27 nm2 per molecule. Properties calculated from the model are in good agreement with available data on bilayer systems at a comparable surface density. The average conformation of the alkyl chains is examined in some detail and compared with recently proposed models of the chain conformation in the ‘‘fluid’’ phase of lipid bilayers.

On defects in different phases of two-dimensional lipid bilayers

On defects in different phases of two-dimensional lipid bilayers

Nonplanar conformers and the phase behavior of solid n-alkanes

Solidsolid phase transitions of the odd n-alkanes n-C17H36 through n-C29H60 were studied by using differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Two phase transitions were found in C25, C2,, and C29 in addition to the previously reported highest-temperature solid-solid transition (the so-called rotator transition). IR spectra revealed that, as the temperature is raised, the concentration of nonplanar conformers successively increases through each phase transition. Three types of nonplanar have been identified in the highest-temperature phase of all the n-alkanes: (gt ...), kink (...gtg'...), and (...gg...). The end-gauche defect was observed in the lower-temperature phases as well. Kink conformers, however, were observed only in the highest-temperature phase while double-gauche were found in measurable concentrations only within a few degrees of the melting point. The concentrations of nonplanar conformers in the highest-temperature phases increase with increasing chain length. For example, roughly 70% of C29 molcules are nonplanar prior to melting, in contrast to 5-10% for C17. The relationship between the existence of nonplanar conformers and the various distinct solid phases presents a major puzzle. Normal alkanes undergo a remarkable series of solidsolid phase transitions prior to melting. Analogous premelting transitions are also found in a number of more complex systems which contain hydrocarbon chains as major constituents. These systems include polyethylene,' variously substituted alkanes,2 and biological ~nembranes.~ In the latter cases, the phase changes are believed to be intimately related to the state of the hydrocarbon component. For example, current models of the lipid bilayer phase transitions require detailed consideration of the changes in conformation of the alkane chains4 Since the n-alkanes themselves are the sim- plest of these chain-molecule solids, they are a natural starting point for understanding the premelting transitions exhibited by all of these systems. The phase behavior of even the n-alkanes is complex. All odd n-alkanes between C9 and C45 undergo at least one premelting phase transition, and the longer members show no less than four high-temperature solid phases in addition to the low-temperature crystalline phases5 The nature of these phases is not well un- derstood although it is clear that the higher-temperature phases involve increasing degrees of disorder. By here we mean any deviation from the regular arrangement of all-trans chains found in the low-temperature solid. In this paper we focus mainly on one aspect of the disordering processes occurring in these solids-that involving conformational changes. We show that infrared spectroscopy is sensitive to the presence of various nonplanar (not all-trans) conformers and to some types of intermolecular order. We will find that disorder occurs in a series of apparently solid phases. The question then arises how can the apparent short-range implied by these nonplanar conformations be reconciled with the existence of a series of phases showing long-range order? This question which is fundamental to the understanding of the more complex systems such as biolipid bilayers will be taken up again in the Conclusion. The body of this paper presents the infrared spectra of the alkanes as a function of temperature with an analysis of the conformational defects seen in the various phases.

Size dependence of the translational diffusion of large integral membrane proteins in liquid-crystalline phase lipid bilayers. A study using fluorescence recovery after photobleaching.

The translational diffusion of bovine rhodopsin, the Ca2+-activated adenosinetriphosphatase of rabbit muscle sarcoplasmic reticulum, and the acetylcholine receptor monomer of Torpedo marmorata has been examined at a high dilution (molar ratios of lipid/protein greater than or equal to 3000/1) in liquid-crystalline phase phospholipid bilayer membranes by using the fluorescence recovery after photobleaching technique. These integral membrane proteins having molecular weights of about 37 000 for rhodopsin, about 100 000 for the adenosinetriphosphatase, and about 250 000 for the acetylcholine receptor were reconstituted into membranes of dimyristoylphosphatidylcholine (rhodopsin and acetylcholine receptor), soybean lipids (acetylcholine receptor), and a total lipid extract of rabbit muscle sarcoplasmic reticulum (adenosinetriphosphatase). The translational diffusion coefficients of all the proteins at 310 K were found to be in the range (1-3) X 10(-8) cm2/s. In consideration of the sizes of the membrane-bound portions of these proteins, this result is in agreement with the weak dependence of the translational diffusion coefficient upon diffusing particle size predicted by continuum fluid hydrodynamic models for the diffusion in membranes [Saffman, P. G., & Delbrück, M. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 3111-3113]. Lipid diffusion was also examined in th same lipid bilayers with the fluorescent lipid derivative N-(7-nitro-2,1,3-benzoxadiazol-4-yl)dimyristoylphosphatidylethanolamine. The translational diffusion coefficient for this lipid derivative was found to be in the range (9-14) X 10(-8) cm2/s at 310 K. In consideration of the dimensions of the lipid molecule, this value for the lipid diffusion coefficient is in agreement with the continuum fluid hydrodynamic model only if a near-complete slip boundary condition is assumed at the bilayer midplane. Alternatively, kinetic diffusion models [Träuble, H., & Sackmann. E. (1972) J. Am. Chem. Soc. 94, 4499-4510] may have to be invoked to explain the lipid diffusion behavior.

Involvement of spectrin in the maintenance of phase-state asymmetry in the erythrocyte membrane

The fluorescent probe merocyanine 540 does not stain the plasma membrane of normal human or murine erythrocytes, nor of genetically abnormal human spherocytic erythrocytes. It does, however, stain erythrocyte membranes in several systems in which the underlying spectrin network is altered or missing. Because of the greater affinity of merocyanine 540 for fluid—phase lipid bilayers, these results suggest that the external leaflet of erythrocyte membranes becomes more disordered upon alteration or loss of the internal spectrin network. Analysis of the transbilayer arrangement of membrane phospholipids by digestion with phospholipase A2 suggests that lipid compositional asymmetry of the erythrocyte membrane is responsible for a phase-state asymmetry between the two lipid leaflets, and that spectrin is required to maintain this asymmetry and the gel-like state of the external leaflet.

Reconstitution in planar lipid bilayers of a Ca2+-dependent K+ channel from transverse tubule membranes isolated from rabbit skeletal muscle.

Addition of membrane vesicles prepared from transverse tubule (T-tubule) membranes of rabbit skeletal muscle to the aqueous phase of a planar lipid bilayer induces a stepwise increase in conductance. This conductance is both voltage and Ca2+ dependent. At 1 mM Ca2+, the steady-state conductance is maximal at voltages higher than +20 mV and decreases for more negative voltages. (Voltages refer to the side to which the vesicles are added, cis) Decreasing the Ca2+ concentration reversibly shifts the conductance-voltage curve toward the right along the voltage axis. Furthermore, Ca2+ can activate the conductance only if added to the cis compartment. Neither Mg2+, Ba2+, nor Cd2+ can activate the conductance induced by T-tubule vesicles. Addition of 5 mM tetraethylammonium ion to the trans, but not the cis, side abolishes the T-tubule-induced conductance. The Ca2+-dependent conductance appears as a consequence of ionic channel formation. Single-channel activity appears in bursts followed by periods of time in which the channel remains "silent". The conductance of the open channel averages 226 pS in 0.1 M KC1 and is voltage and Ca2+ independent. However, the fraction of time that the channel remains in the open state is voltage and Ca2+ dependent in a manner that parallels the voltage and Ca2+ dependence of the multichannel membrane. The channel is 6.6 times more permeable to K+ than to Na+ and is impermeable to C1-.

Theory of the Main Lipid Bilayer Phase Transition

Machine learning (ML) is transforming all areas of science. The complex and time-consuming calculations in molecular simulations are particularly suitable for an ML revolution and have already been profoundly affected by the application of existing ML ...Read More