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E Sackmann

Publications and source records attributed to E Sackmann.

At least 91 records · Page 5Linked to original sources
PubMed1990

Specular reflection of neutrons at phospholipid monolayers. Changes of monolayer structure and headgroup hydration at the transition from the expanded to the condensed phase state.

The specular neutron reflection technique has been applied for the first time to study the structure and head group hydration of a phospholipid monolayer (dimyristoylphosphatidylcholine containing negatively charged phospholipids) in the condensed and expanded state. By variation of the contrast of the subphase to that of the air it is shown that at the transition from the condensed to the expanded state the carboxyl bonds of the glycerol backbone are hydrated leading to a strong structural change of the headgroup. The total monolayer thickness in the condensed state is 22.5 +/- 1 A (tilt angle 32 +/- 6 degrees) and decreases to 19.5 +/- 1 A in the expanded state. The mean molecular volume increases from 1190 +/- 50 A3 to 1250 +/- 50 A3.

Deuterium↗
PubMed1989

Solubilization of DMPC and DPPC vesicles by detergents below their critical micellization concentration: high-sensitivity differential scanning calorimetry, Fourier transform infrared spectroscopy and freeze-fracture electron microscopy reveal two interaction sites of detergents in vesicles.

The interaction of sodium deoxycholate, sodium cholate and octyl glucoside with sonicated vesicles of L alpha-dimyristoyl-phosphatidylcholine (DMPC) and L alpha-dipalmitoylphosphatidylcholine (DPPC) at concentrations below the critical micellization concentration (cmc) of the detergents was studied by high-sensitivity DSC (hs-DSC), Fourier transform infrared spectroscopy (FT-IR) and freeze-fracture electron microscopy. The two phospholipids exhibited a striking different thermotropic behaviour in the presence of these detergents. For DPPC vesicles, the detergents were found to interact exclusively in the aqueous interface region of the bilayer below the membrane saturation concentration Rsat while in DMPC vesicles two coexisting interaction sites below this concentration persist. These are detergents which interact at the aqueous interface region (site 1) and in the acyl chain region (site 2) of the DMPC vesicles. The partition coefficients K of the detergents between DPPC vesicles and the water phase were calculated from the hs-DSC results at two detergent/phospholipid molar ratios Rtot less than or equal to Rsat as 0.35, 0.049 and 0.040 mol-1 for sodium deoxycholate, sodium cholate and octyl glucoside, respectively. In contrast, for DMPC the K values for Rtot less than or equal to Rsat were found to be dependent on Rtot due to the occupation of site 2 by the detergents above a certain Rtot. The model is discussed on the basis of the detergents free energies of transfer from the water phase to site 1 and site 2 of the vesicles, respectively. The solubilization behaviour of DPPC vesicles, dependent on whether the total detergent concentration is above or below the cmc at Rsat, differed significantly as revealed by hs-DSC. This suggests that in the latter case an additional hydrophobic effect could facilitate the formation of disc shaped mixed micelles. Moreover, this different behaviour was employed to measure the cmc values of the detergents studied in the presence of the vesicles by hs-DSC.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1989

Sensitive detection of protein adsorption to supported lipid bilayers by frequency-dependent capacitance measurements and microelectrophoresis.

In the first part, we report experiments which enable the sensitive detection of protein adsorption to lipid bilayers deposited onto chromium electrodes on glass substrates by frequency-dependent capacitance measurements. The sensitivity of the present type of sensor (better than 0.3 nm average protein layer thickness) is at least equivalent to that of ellipsometry. A high specific resistance of the supported bilayer of (1-5).10(5) omega.cm2 is achieved by deposition of a tightly packed (crystalline) cadmium arachidate monolayer in contact with the substrate, whereas the outer monolayer can be more loosely packed (fluid phase or state of fluid-solid coexistence) which is essential for the incorporation of receptors. In the present work, charged lipids are incorporated as nonspecific receptors for polylysine and cytochrome c. The capacitance measurements provide a very sensitive test of the tightness and the long-time stability of the supported bilayers and, in combination with ellipsometric thickness measurements, enable estimations of dielectric properties of protein layers (such as the permittivity). In the second part, we report first electrophoresis experiments in asymmetric bilayers on substrates which enable simultaneous measurements of lateral diffusion coefficients and frictional coefficients between monolayers. The potential application of the electrophoretic effect for the differentiation between different receptors and the amplification of signals in biosensors is discussed.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Structural properties of a phosphatidylcholine-cholesterol system as studied by small-angle neutron scattering: ripple structure and phase diagram.

Small-angle neutron scattering has been used to study structural features of lamellar bilayer membranes of dimyristoylphosphatidylcholine (DMPC) and DMPC mixed with various amount of cholesterol. The studies were recorded at a fixed hydration level of 17% 2H2O, i.e. just below saturation. Bragg reflections gives information on the ripple structure and on the bilayer periodicity. The crystalline Lc phase, which was stabilized after long time storage at low temperature, exhibits major small angle scattering when cholesterol is mixed into the membrane. The intermediate P beta' gel-phase, which is characteristic by the rippled structure, is dramatically stabilized by the introduction of cholesterol. The ripple structure depends significantly both on the cholesterol content and on the temperature. At high temperatures, T greater than 15 degrees C, the inverse ripple periodicity varies basically linearly with cholesterol content, and approach zero (i.e. periodicity goes to infinite) at 20 mol% cholesterol, approximately. At lower temperatures the correlation is more complex. The data indicate additional phase boundaries below 2 mol% and at approx. 8 mol%. Secondary rippled structures are observed in the low temperature L beta'-phase for cholesterol content below approx. 8 mol%. The data gives detailed insight into the phosphatidylcholine cholesterol phase diagram, which is discussed on the basis of a simple model in which the cholesterol complexes are fixed to the defect stripes of the rippled structure.

Cholesterol↗
PubMed1988

Interaction of insulin receptors with lipid bilayers and specific and nonspecific binding of insulin to supported membranes.

In the first part, we study the interaction of the insulin receptor with model membranes of dimyristoylphosphatidylcholine (DMPC) by various techniques, including calorimetry, densitometry, static light scattering, and electron microscopy. By analyzing the pronounced depression of the lipid chain melting transition in terms of the Van Laar-Hildebrand theory of regular dilute solutions, an (exothermic) interaction energy of Wp = 2000 kJ.mol-1 is found for the receptor and of WL = 0.6 kJ.mol-1 for the lipid. This is interpreted in terms of an adsorption of the 2 hydrophilic head groups of the receptor to the membrane surface so that 1 protein interacts with about 2000 lipids. This number is verified by freeze-fracture electron microscopy. Binding of insulin induces a remarkable decoupling of the receptor head group from the membrane, pointing to a pronounced conformational change. In the second part, we introduce a simple fluorescence technique by which adsorption isotherms of water-soluble and fluorescent-labeled substrates, such as insulin, to membranes may be determined. It is based on the selective evanescent field excitation of ligands adsorbed to supported planar bilayers on argon-sputtered glass plates. These are deposited by the monolayer transfer technique or by vesicle condensation. The reconstituted receptor exhibits a weak (binding constant Kw = 3 X 10(9) L.M-1) and a strong (binding constant Ks greater than 10(10) L.M-1) binding site. Insulin exhibits a weak but remarkable nonspecific binding to bilayers of pure DMPC and DMPC containing 20% positively charged lipid and a strong binding to DMPC containing negatively charged lipids such as phosphatidylserine or ganglioside (GT1b).(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry↗
PubMed1988

On the measurement of shear elastic moduli and viscosities of erythrocyte plasma membranes by transient deformation in high frequency electric fields.

We present a new method to measure the shear elastic moduli and viscosities of erythrocyte membranes which is based on the fixation and transient deformation of cells in a high-frequency electric field. A frequency domain of constant force (arising by Maxwell Wagner polarization) is selected to minimize dissipative effects. The electric force is thus calculated by electrostatic principles by considering the cell as a conducting body in a dielectric fluid and neglecting membrane polarization effects. The elongation A of the cells perpendicular to their rotational axis exhibits a linear regime (A proportional to Maxwell tension or to square of the electric field E2) at small, and a nonlinear regime (A proportional to square root of Maxwell tension or to the electric field E) at large extensions with a cross-over at A approximately 0.5 micron. The nonlinearity leads to amplitude-dependent response times and to differences of the viscoelastic response and relaxation functions. The cells exhibit pronounced yet completely reversible tip formations at large extensions. Absolute values of the shear elastic modulus, mu, and membrane viscosity, eta, are determined by assuming that field-induced stretching of the biconcave cell may be approximately described in terms of a sphere to ellipsoid deformation. The (nonlinear) elongation-vs.-force relationship calculated by the elastic theory of shells agress well with the experimentally observed curves and the values of mu = 6.1 x 10(-6) N/m and eta = 3.4 x 10(-7) Ns/m are in good agreement with the micropipette results of Evans and co-workers. The effect of physical, biochemical, and disease-induced structural changes on the viscoelastic parameters is studied. The variability of mu and eta of a cell population of a healthy donor is +/- 45%, which is mainly due to differences in the cell age. The average mu value of cells of different healthy donors scatters by +/- 18%. Osmotic deflation of the cells leads to a fivefold increase of mu and 10-fold increase of eta at 500 mosm. The shear modulus mu increases with temperature showing that the cytoskeleton does not behave as a network of entropy elastic springs. Elliptic cells of patients suffering from elliptocytosis of the Leach phenotype exhibit a threefold larger value of mu than normal discocytes of control donors. Cross-linking of the spectrin by the divalent S-H agents diamide (1 mM, 15 min incubation) leads to an eightfold increase of mu whereas eta is essentially constant. The effect of diamide is reversed after treatment with S-S bond splitting agents.

Diamide↗
PubMed1987

Electrostatic coupling of spectrin dimers to phosphatidylserine containing lipid lamellae.

We studied the interaction of spectrin dimers from human erythrocytes with (bilayer and monolayer) model membranes of mixtures of dimyristoylphosphatidylethanolamine, dimyristoylphosphatidylcholine, and dimyristoylphosphatidylserine (DMPS) by densitometric evaluation of phase transitions and phase boundaries, film balance experiments, and microfluorescence. We demonstrate that spectrin readily adsorbs to mixed bilayers and monolayers even in the presence of small DMPS concentrations (30 mol %) whereas no appreciable interaction with lamellae containing zwitterionic lipids alone is observed. The selectivity of the DMPS/spectrin interaction is established by quantitative evaluation of the shifts of the phase boundaries (liquidus and solidus line) caused by the lipid/protein interaction as a function of the composition of the binary lipid mixtures. Quantitative information about the free energy of the lipid/protein interaction is obtained by computer simulation of the phase diagram of the lipid mixture in the absence or in the presence of a very small molar fraction of the protein and comparison of calculated and measured shifts. A binding energy of about 10(-17) J per spectrin molecule is found. The present perturbation method can be generalized to study selective lipid/protein interaction mechanisms in ternary or higher component mixtures. The present results provide evidence that in addition to the binding to band III, spectrin may also couple directly to the lipid moiety of the inner monolayer of erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimyristoylphosphatidylcholine↗
PubMed1986

Flicker spectroscopy of erythrocytes. A sensitive method to study subtle changes of membrane bending stiffness.

Frequency analysis of thermally excited surface undulations of erythrocytes leading to the flicker phenomenon is applied to determine biochemically and physically induced modulations of the membrane curvature elasticity. Flicker spectra of individual cells fixed to the window of a flow chamber by polylysine are taken by phase contrast microscopy, enabling investigations of the reversibility of the structural modifications. The spectra may be approximated by Lorentzian lines in most cases. By measuring the amplitude (at zero frequency) and the line width, effects of the structural changes on the curvature elastic constant, Kc, and the wavelength distribution of the undulations may be studied separately. Effect of physically induced modifications: The temperature dependence of the flicker spectra are taken from 10 degrees C to 37 degrees C. Above 20 degrees C, Kc decreases with increasing temperature whereas the reverse holds below this limit. The latter anomalous behaviour is explained in terms of a conformational change associated with protein and lipid lateral phase separation. The bending stiffness increases when the cells swell osmotically, owing to surface tension effects. The dependence of the flicker spectra on the viscosity of the suspension medium agrees with the theoretical prediction. Biochemically and drug induced modifications: 5 vol% of ethanol leads to a pronounced and reversible suppression of the long wavelength undulations without altering the discoid cell shape and without affecting the bending stiffness appreciably. Adsorption of dextran to the glycocalix increases Kc by a factor of 1.6 at saturation. The bending stiffness is increased by a factor of 1.3 after cross-linking the proteins with the SH-oxidizing agent diamid. Injection of Ca++ into the cell via ionophores evokes (within 10 min) the formation of fine--probably spectrin free--spicules. This leads to an increase in Kc by a factor of 1.3 which is explained in terms of a lateral condensation of the spectrin/actin network. The spicule formation and Kc change is completely reversible (within 2 min) after perfusion with Ca++-free buffer. Cholesterol depletion leads first to a continuous increase in Kc without change of the cell shape whereas a sudden discocyte- to echinocyte transformation sets in below a critical steroid content. The latter transition is also observed in cell suspensions and is reminiscent of a phase transition. The anti-tumor drug actinomycin D evokes an increase in the bending stiffness Kc by a factor of two, suggesting that its effect is at least partially due to a modulation of the membrane structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium↗
PubMed1985

Small-angle neutron scattering study of lateral phase separation in dimyristoylphosphatidylcholine-cholesterol mixed membranes.

The small-angle neutron scattering (SANS) technique developed previously is used to study the lateral phase separation in dimyristoylphosphatidylcholine (DMPC)-cholesterol mixed vesicles in the L alpha (35 degrees C) and L beta' (7 degrees C) phase of DMPC. To increase the sensitivity of the previous method, we apply the so-called inverse contrast variation technique where contrast matching is performed at a constant H2O/D2O ratio by varying the ratio of DMPC with deuterated and protonated hydrocarbon chains. Phase boundaries can be determined to an accuracy of +/- 0.5 mol %. In parallel experiments phase separation in the L beta' phase was also studied by freeze-fracture electron microscopy. For DMPC in the L alpha phase complete miscibility is clearly established up to cholesterol molar fractions of xc = 0.14. Strong evidence is provided that this is also the case up to xc approximately equal to 0.45. Cholesterol is no longer soluble above this limit and precipitates as small crystallites. For the L beta' phase (7 degrees C) phase boundaries are clearly established at xc1 = 0.08 and xc2 = 0.24, and very strong evidence is provided for two additional boundaries at xc3 = 0.435 and xc4 approximately equal to 1.0. At 0 less than or equal to xc less than or equal to xc1 the mixture forms a tilted solid solution in both the L beta' and P beta' phase while at xc1 less than or equal to xc less than or equal to xc2 this phase coexists with a nontilted mixture containing 24 mol % cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol↗
PubMed1984

Variation of frequency spectrum of the erythrocyte flickering caused by aging, osmolarity, temperature and pathological changes.

Frequency spectra of the surface undulations (flickering) of erythrocyte plasma membranes are measured by direct spectral analysis of the intensity fluctuations of the light passing the cells in a phase contrast microscope. Spectra are taken as a function (1) of the temperature (2) of the viscosity and osmolarity of the outer medium (3) of the aging of cells and (4) of pathological transformations. The spectra are approximately superpositions of two Lorentzian lines. At large frequencies, f, the spectra follow f-2. This behaviour can be interpreted in terms of cell thickness fluctuations caused by thermally excited membrane undulations provided the range of wavelengths is small. The undulations are determined by the membrane curvature elasticity while the lateral tension is negligibly small for cells of discoid shape. The technique presented allows accurate measurements of relative curvature (bending) elastic constants. The spectra of freshly drawn cells are remarkably reproducible. Aging of the cells in the medium leads to an increase in the curvature elastic constant. A decrease in osmolarity causes a reduction in the intensity and line width of the spectra and the flickering vanishes if the cell approaches a spherical shape. The effect of temperature between 10 and 40 degrees C is astonishingly small with the exception of a sudden increase in the amplitude with increasing temperature at 35 degrees C. The flicker spectra of a large fraction of the cells from patients suffering from cronical alcoholism exhibit a reduced line width or an increase in the curvature elastic constant.

Disease↗
PubMed1984

Lateral diffusion of lipids and glycophorin in solid phosphatidylcholine bilayers. The role of structural defects.

The lateral mobility of the lipid analog N-4-nitrobenzo-2-oxa-1,3 diazole phosphatidylethanolamine and of the integral protein glycophorin in giant dimyristoylphosphatidylcholine vesicles was studied by the photobleaching technique. Above the temperature of the chain-melting transition (Tm = 23 degrees C), the diffusion coefficient, Dp, of the protein [Dp = (4 +/- 2) X 10(-8) cm2/s at 30 degrees C] was within the experimental errors equal to the corresponding values DL of the lipid analog. In the P beta 1 phase the diffusion of lipid and glycophorin was studied as a function of the probe and the protein concentration. (a) At low lipid-probe content (cL less than 5 mmol/mol of total lipid), approximately 20% of the probe diffuses fast (D approximately equal to 10(-8) - 10(-9) cm2/s), while the mobility of the rest is strongly reduced (D less than 10(-10) cm2/s). At a higher concentration (cp approximately 20 mmol), all probe is immobilized (D less than 10(-10) cm2/s). (b) Incorporation of glycophorin up to cp = 0.4 mmol/mol of total lipid leads to a gradual increase of the fraction of mobile lipid probe due to the lateral-phase separation into a pure P beta 1 phase and a fraction of lipid that is fluidized by strong hydrophilic lipid-protein interaction. (c) The diffusion of the glycophorin molecules is characterized by a slow and a fast fraction. The latter increases with increasing protein content, which is again due to the lateral-phase separation caused by the hydrophilic lipid-protein interaction. The results are interpreted in terms of a fast transport along linear defects in the P beta 1 phase, which form quasi-fluid paths for a nearly one dimensional and thus very effective transport. Evidence for this interpretation of the diffusion measurements is provided by freeze-fracture electron microscopy.

Diffusion↗
PubMed1984

Lateral diffusion and phase separation in two-dimensional solutions of polymerized butadiene lipid in dimyristoylphosphatidylcholine bilayers. A photobleaching and freeze fracture study.

Mixed vesicles of dimyristoylphosphatidylcholine (DMPC) and a polymerizable lipid containing one diene group per chain are studied by freeze fracture electron microscopy and by the photobleaching (fluorescence recovery after photobleaching) technique. Large thin-walled vesicles of some micron in diameter become more stable after photochemical polymerization. Before polymerization bilayers of the diene lipid exhibit a liquid crystal-to-gel transition at Tg = 31 degrees C. Upon polymerization the transition remains but shifts to a slightly higher temperature (Tg* = 34 degrees C). The transitions in both cases are accompanied by a freezing in of the lateral mobilities. The mixed vesicle exhibits lateral phase separation after polymerization. Before polymerization the two lipids appear miscible at all compositions in the fluid state and at DMPC concentrations at or below 50 mol % in the solid state. After polymerization a two-dimensional solution of the polymer in DMPC is obtained at T greater than Tg*, while lateral phase segregation into DMPC-rich domains and patches of the polymer is observed at T less than Tg*. The domain structure appears identical irrespective of whether polymerization is performed at T greater than Tg or at T less than Tg. A typical value of the diameter of the polymerized lipid domains (approximately 400 A) indicates a rather small aggregation number (N less than 100 monomers). The lateral diffusion coefficient in butadiene-lipid bilayers only decreases from D1 = 3.10(-7) cm2/s to D1 = 8.10(-8) cm2/s (that is by a factor of 4) upon polymerization. This is consistent with the freeze fracture finding of a small aggregation number. We point out the similarities of the mixed vesicles with plasma membranes coupled to the cytoskeleton.

Butadienes↗
PubMed1984

On the role of lipid-bilayer elasticity for the lipid-protein interaction and the indirect protein-protein coupling.

The present paper deals with the curvature (or splay) elasticity of lipid bilayers and its possible consequences for the microscopic organization of membranes. Experimental studies of the microstructure of lipid-lipid and lipid-protein mixtures are reported and discussed in terms of this type of membrane elasticity. In particular, evidence is provided that the elastic distortion of lipid bilayers caused by the incorporation of proteins can lead to mechanisms of the indirect protein-protein interaction. Finally the question is discussed whether these mechanisms could also play a role for the formation of enzyme complexes in biological membranes.

Dimyristoylphosphatidylcholine↗
PubMed1983

Protein-mediated lipid transfer. The effects of lipid-phase transition and of charged lipids.

The protein-mediated phospholipid exchange between small unilamellar vesicles was investigated by fluorescence polarization measurements with diphenylhexatriene as optical probe. Thermotropic phase-transition measurements were taken after mixing two vesicle preparations of distinct and different phase-transition temperatures or having different states of charge. From the heights of each phase-transition step, we were able to follow the lipid-exchange process in the presence, as well as in the absence (natural exchange), of so-called transfer protein isolated from beef liver. A strong enhancement of the lipid transfer was observed at the corresponding lipid-phase-transition temperature, which is explained by the presence of fluctuating fluid and ordered domains co-existing at the lipid-phase-transition temperature. A unidirectional lipid transfer of the neutral component was observed between negatively charged phosphatidic acid and neutral phosphatidylcholine vesicles. Fluorescence polarization measurements showed the disappearance of the phosphatidylcholine phase transition, whereas the phosphatidic acid phase transition broadened and its phase transition temperature became lower.

Androgen-Binding Protein↗
PubMed1983

A simple assay to study protein-mediated lipid exchange by fluorescence polarization.

We investigated the protein-mediated phospholipid transfer between small vesicles by fluorescence polarization measurements with diphenylhexatriene as optical probe. Thermotropic-phase-transition curves were taken after mixing two vesicle preparations of lipids exhibiting different gel-to-liquid phase transitions. From the heights of each phase-transition step we were able to follow the lipid transfer process without separating the two vesicle preparations.

Carrier Proteins↗
PubMed1981

Small-angle neutron scattering study of lipid phase diagrams by the contrast variation method.

A small-angle neutron scattering (SANS) study of slightly sonicated liposomes of binary lipid mixtures is presented. It is demonstrated that the neutron scattering of lipid lamellae may be analyzed in terms of the Kratky--Porod model of scattering by two-dimensional systems. The contrast variation technique may thus be applied in order to study the structure and phase diagrams of lipid layers not disturbed by heavy sonication. The thickness of isolated bilayers is measured, and molar volumes of pure lipid phases are determined. Mixtures of deuterated dimyristoylphosphatidylcholine with (1) protonated dipalmitoylphosphatidylcholine and (2) protonated distearoylphosphatidylcholine, respectively, are studied. Excess volumes of lipid mixtures are determined by the contrast variation. For the first mixture positive excess volumes of +86 A3 in the crystalline phase (5 degrees C) and of +49 A3 in the fluid phase (35 degrees C) are obtained. These large positive excess volumes are interpreted in terms of free volume creation at the interface between the monolayers, which indicates that the polar head groups are rather fixed with respect to the lipid--water interface. We show that the phase boundaries at a given temperature may be determined by performing contrast variation experiments for two mixtures with different initial composition. Good agreement with existing experimental data is observed for the first mixture. A miscibility gap is established in the crystalline state of the second mixture. A most interesting result is the finding of an immiscibility in the fluid state. This is interpreted in terms of critical concentration fluctuations caused by the critical demixing point of the solid-state miscibility gap hidden below the liquidus line.

Deuterium↗
PubMed1981

Translational mobility of glycophorin in bilayer membranes of dimyristoylphosphatidylcholine.

The translational diffusion of the integral membrane sialoglycoprotein from erythrocyte membranes, glycophorin, incorporated into bilayer membranes of dimyristoyl-phosphatidylcholine at a protein/lipid molar ratio of 1:4500 was examined by using the fluorescence redistribution after photobleaching technique. A plot of the diffusion coefficient vs. temperature shows a sharp decrease in the rate of diffusion at about 15 degrees C. This sharp diffusion transition is at a temperature some 9 degrees C lower than the calorimetrically measured lipid gel-liquid crystalline phase transition temperature of the system. The difference between the diffusion transition temperature and the lipid phase transition temperature is attributed toi a localized fluidizing effect of the protein upon the gel phase lipid. The value of the diffusion coefficient above 15 degrees C was found to be (1-2) x 10(-8) cm(2)s(-1), and below 15 degrees C it was lower than about 5 x 10(-11)cm(2)s(-1). The fluorescence recovery in the bleached area as a consequence of diffusional redistribution appeared to be due to a single diffusing species at temperatures above 15 degrees C and due to more than one diffusing species below this temperature.

Dimyristoylphosphatidylcholine↗