Ultracentrifugation of hydrated egg lecithin in benzene solution

Estimations of molecular weights from sedimentation equilibrium experiments indicate that the degree of aggregation of egg lecithin in benzene solutions increases with increasing addition of water. The molecular weight rises monotopically from about 14,000 in the anhydrous state to about 57,000 at a water/lecithin ratio of 0.31. Sedimentation coefficients were shown to behave in the same manner. Frictional coefficients obtained from the combined results fail to indicate definite differences in asymmetry; however, they seem to indicate that the aggregates in all stages are compact in shape.     

NMR Investigations of the interaction of water with lecithin in benzene solutions

NMR investigations of ¹H (chemical shifts, line widths) and of ³¹P (relaxation times, T₁) performed on the three-component system of lecithin-benzene-water show that there is an interaction of water with the phosphate group in two regions of different mobility and structure. A fast exchange of the water molecules takes place between both regions. The region of strong interaction involves about 2 and that of the weaker interaction about 5 water molecules per lecithin molecule. When the water concentration is increased a third region is formed which is assigned to the water molecules that are located beyond the two regions of interaction with the phosphate group, but within the micelle. This water has a different structure from that of the second region of interaction with the phosphate group and may also have a different mobility.Addition of water increases the motion of the head groups of the lecithin molecules. This is due to a loosening of the packing of lecithin molecules.     

Interaction between RNAs from different sources and egg lecithin liposomes

The interaction of RNAs of molecular weight ranging between 15,000 and 30,000 with egg lecithin large and small unilamellar liposomes has been investigated. Torula and tRNA proved to be incorporated to a similar extent but no linear relationship between molecular weight and percent of incorporation was demonstrated. A relationship between percent of secondary structure of RNA and its ability to be trapped in SUV liposomes is suggested.     

Interaction of amphotericin B with monolayers of egg lecithin and cholesterol: polorized absorption spectra

Polarized absorption spectra have been obtained of the antibiotic polyene, amphotericin B, interacting with monolayers of egg lecithin, cholesterol and equimolar egg lecithin-cholesterol at low and high surface pressures. An expression is derived which enables the determination from the polarization data of the orientations of the transition moments of the polyene absorption bands at 4077 and 3645 Å. For some of the systems the 3645-Å band is replaced by a previously unreported band appearing between 3610 and 3632 Å. The orientation of the 4077-Å transition moment (parallel to the long molecular axis) is found to vary from an angle of 64 ° with the surface for the low-pressure monolayers of cholesterol to 21 ° for the high-pressure films of egg lecithin-cholesterol. For the band between 3610 Å and 3645 Å, the angle varies from 90 ° for cholesterol to 18 ° for the high-pressure mixed-lipid film. It is found that a large increase in surface pressure of the cholesterol and egg lecithin-cholesterol monolayers causes a decrease in the angle of the 4077-Å moment for both films and that of the higher energy moment for the mixed film. Increasing the content of cholesterol in these monolayers rotates the orientation of the transition moments for both bands toward the surface normal, the change being greatest for the low-pressure films. The effectiveness of amphotericin B in lowering the surface tension of these lipid monolayers is related to its binding, orientation and extent of penetration. For low-pressure cholesterol films where the surface interaction with the polyene is greatest, the binding and penetration are large and the polyene molecule is oriented with its long dimension nearly perpendicular to the surface.     

Partial specific volumes of lipid and water in mixtures of egg lecithin and water.

We describe in this paper measurements of the partial specific volumes of lipid (upsilon L) and water (upsilon W) in mechanical mixtures of egg yolk lecithin and water over a range of hydrations (5-55 wt% water) that includes the region at which excess water appears. upsilon L and upsilon W are found to be very nearly 1 cm3/g over the entire range. The water activities of the mixtures were also determined and found to be the same as for lipid deposited as oriented multilayers on solid substrates.     

Interaction of aldolase A with lecithin liposomes

The aldolase A binding to the lecithin liposomes (Kd = 2.4 +/- 0.1 X 10(-3) M) has been shown by the fluorescence and tryptophan phosphorescence at the room temperature. The interaction is accompanied by an increase in the phospholipid bilayer microviscosity, and some conformational changes in the hydrophobic part of the enzyme, pronouncing themselves in Trp-147 environment rigidity, decrease. The observation of membrane viscosity vs. incubation time revealed practically instant enzyme-membrane interaction and no gradual incorporation. The accessibility of the NAD-binding domain of aldolase for NADH in the liposome presence remains unaltered.     

Tin compounds interaction with membranes of egg lecithin liposomes

This work is a continuation of earlier research concerning the influence of tin compounds on the dynamic properties of liposome membranes produced with lecithin hen egg yolks (EYL). The experiments were carried out at room temperature (about 25 degrees C). Four tin compounds were chosen, including three organic ones, (CH3)4Sn, (C2H5)4Sn and (C3H7)3SnCl, and one inorganic, SnCl2. The investigated compounds were admixed to water dispersions of liposomes. The content of the admixture changed within the range 0 mol-% to 11mol-% in proportion to EYL. Two spin probes were used in the experiment: 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 2-ethyl-2-(15-methoxy-15-oxopentadecyl)-4,4-dimethyl-3-oxazolidinyloxyl (16-DOXYL-stearic acid), which penetrated through different areas of the membrane. It was found that tin compounds containing chlorine were the most active in interaction with liposome membranes. In the case of (C3H7)3SnCl, after exceeding 4% admixture content, an additional line appeared in the spectrum of the TEMPO probe which can be a result of formation of domain structures in the membranes of the studied liposomes. Compounds containing chlorine are of ionized form in water solution. The obtained results can thus mean that the activity of admixtures can be seriously influenced by their ionic character. In case of an admixture of non-ionic compounds the compound with a longer hydrocarbon chain displayed a slightly stronger effect on the spectroscopic parameters of the probes.     

Thermotropic behavior of liposomes from egg yolk lecithin, hydrogenized egg yolk lecithin and their mixtures

The thermotropic properties of multilamellar liposomes from egg yolk lecithin, hydrogenized egg yolk lecithin and several mixtures of these two lipids were studied with the application of excimer--forming optical probe pyrene and microcalorimetry. It was discovered that when the proportion of the egg yolk lecithin in the lipid mixture was raised the temperature of the main phase transition reduced. For all this, independent of the lipid mixture composition when the temperature was raised, apparently, polarity of pyrene microenvironment in the liposomes bilayers decreased. On the basis of the analysis of solidus and liquidus curves obtained from calorimetric studies of the lipid mixtures and bend points of Arrhenius anamorphose obtained during the pyrene excimer formation measurements some conclusions were made about the role of unmodified and hydrogenized egg yolk lecithin cluster formation in the determination of thermotropic properties of the liposomes from the above two lipids mixtures. High temperature phase transition discovered for the egg yolk lecithin while measuring the pyrene excimer formation is proposed to be closely connected with temperature-dependent changes in the organization of phospholipid heads on the interphase bilayer/H2O solution.     

Studies on spin-labelled egg lecithin dispersions

ESR spectra of egg lecithin dispersions labelled with 5-nitroxide stearic acid are recorded with a 50 G field sweep, and also with a new technique which “expands” the spectrum by (1) recording pairs of adjoining peaks with a smaller field sweep and (2) superposing the common peaks. The expansion technique improves the precision of the order parameters determined from the hyperfine splitting measurements, and may prove useful in future spin label membrane studies.Approximate order parameters are derived to describe the fluidity of fatty acid spin-labelled membranes in those cases where either the inner or outer hyperfine extrema are not well defined. The ability of these expressions to measure the fluidity of labelled egg lecithin dispersions for the temperature range 14–42° C is examined.     

Liposome formation of egg lecithin and its interaction with iodine

The sonicated dispersion of egg lecithin (phosphatidylcholine) in water forms 1:1 molecular complex with iodine, when its concentration is above 1.6 X 10(-5) M. The thermodynamic and spectrophotometric properties of this complex have been determined. The thermodynamic values are: K (25 degrees C) = 1.6 X 10(3) 1 X mol-1, delta G degrees = -18.4 KJ X mol-1, delta H degrees = -27.4 KJ X mol-1 and delta S degrees = -30.0 J X mol-1 X deg-1. The complex shows two absorption bands: one at 293 nm, which is the charge transfer band and the other at 370 nm, which is the blue shifted visible iodine band at 460 nm in water.     

Magnetic anisotropy of egg lecithin membranes.

Magnetic realignment and rotational diffusion of cylindrical egg lecithin vesicles were measured under a phase contrast microscope. The anisotropy of magnetic susceptibility times membrane thickness was calculated from the data for several thin-walled vesicles. The resulting values were assigned to discrete numbers of bilayers. The difference between the susceptibilities parallel and perpendicular to the long axes of the lecithin molecules is deduced to be X parallel - X perpendicular = -(0.28 +/- 0.02) . 10(-8) cgs at 23 degrees C, if a bilayer thickness of 60 A is assumed.     

Action of surfactants on egg lecithin liposomes

The lytic action of several homologous series of surfactants including N-acyl derivatives of the Na-salt of amino acids on the egg lecithin multilamellar liposomes was examined. The affinity for the lipid membrane and the solubilising capacity of the agents were estimated. The contribution of a CH₂ group and that of the polar head group of surfactants to the free energy of the agent's binding to the membrane were evaluated. The results obtained indicate that the contribution of a CH₂ group to the free binding energy depends on the nature of the surfactants' head group. This dependence is attributed to either various localisation of the agent's molecules in the lipid bilayer or to different properties of the agent's hydrocarbon tails. The contributions of the head groups of the surfactants are assumed to reflect the affinity of these head groups for the lecithin polar head group at the membrane interface. The results obtained indicate some degree of specificity involved in the interactions of the head groups.     

Replacing egg yolk with soybean lecithin in the cryopreservation of stallion semen

The objective of this study was to determine whether replacing the egg yolk with soybean lecithin in the Botu-Crio? cryodiluent would maintain the fertility of cryopreserved stallion sperm. Two experiments were performed to evaluate cell freezability. In experiment 1, sperm from 15 stallions were frozen in Botu-Crio? (BC) or Botu-Crio? which contained 45g/L soybean lecithin (BCLS45) in place of the egg yolk. In experiment 2, we compared different concentrations of soybean lecithin: 0, 10.0, 12.5, 15.0, 17.5 and 20.0g/L (BC, BCLS10, BCLS12.5, BCLS17.5 and BCLS20, respectively). In experiment 1, sperm frozen in BC and BCLS45 exhibited similar (P>0.05) percentages of total motile sperm (61% and 61%, respectively); progressively motile sperm (27% and 27%, respectively) and sperm with intact plasma membranes (IMP; 53% and 57%, respectively). Similarly, sperm frozen in BC or BC containing any concentration of soybean lecithin maintained similar (P>0.05) percentages of total motile sperm (61-68%) and progressively motile sperm (27-31%). In the first fertility trial, we used cryopreserved semen from a single stallion was inseminated into mares. The semen from the sperm that were frozen in BC diluent resulted in a higher fertility rate (66%, 16/24) compared to the sperm that were frozen in BCLS45 diluent (17%, 5/29; P<0.01). Similarly, in a second fertility trial, the mares that were inseminated with the sperm that were frozen in BC diluent exhibited a higher fertility rate (66%, 16/24) compared to the mares that were inseminated with the sperm that were frozen in BCLS20 (40%, 10/25; P<0.05). Finally, in a third trial, the sperm that were frozen in BC resulted in a higher fertility rate in mares (75%, 18/24) compared to the sperm that were frozen in BCLS10 (41%, 10/24; P<0.05). Although replacing the egg yolk in the BC cryodiluent with soybean lecithin provided similar laboratory results for stallion sperm, after cryopreservation, the sperm that was frozen with soybean lecithin in the diluent correlated with lower fertility rates. Based on these results, we concluded that the use of BCLS can be used as an alternative diluent for cryopreserving stallion sperm. However, the resulting reduced fertility rate is a matter of concern. Further studies are necessary to clarify the reasons for this decrease in fertility and to determine the optimal lecithin concentration for diluents to freeze stallion sperm.     

Studies on spin-labelled egg lecithin dispersions.

ESR spectra of egg lecithin dispersions labelled with 5-nitroxide stearic acid are recorded with a 50 G field sweep, and also with a new technique which "expands" the spectrum by (1) recording pairs of adjoining peaks with a smaller field sweep and (2) superposing the common peaks. The expansion technique improves the precision of the order parameters determined from the hyperfine splitting measurements, and may prove useful in future spin label membrane studies. Approximate order parameters are derived to describe the fluidity of fatty acid spin-labelled membranes in those cases where either the inner or outer hyperfine extrema are not well defined. The ability of these expressions to measure the fluidity of labelled egg lecithin disperions for the temperature range 14-42 degrees C is examined.