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Biomedical subjects

H Eibl

Publications and source records attributed to H Eibl.

At least 127 records · Page 7Linked to original sources
PubMed1979

The influence of charge on phosphatidic acid bilayer membranes.

A complete titration of phosphatidic acid bilayer membranes was possible for the first time by the introduction of a new anaologue, 1,2-dihexadecyl-sn-glycerol-3-phosphoric acid, which has the advantage of a high chemical stability at extreme pH values. The synthesis of the phosphatidic acid is described and the phase transition behaviour in aqueous dispersions is compared with that of three ester phosphatidic acids; 1,2-dimyristoyl-sn-glycerol-3-phosphoric acid, 1,3-dimyristoylglycerol-2-phosphoric acid and 1,2-dipalmitoyl-sn-glycerol-3-phosphoric acid. The phase transition temperatures (Tt) of aqueous phosphatidic acid dispersions at different degrees of dissociation were measured using fluorescence spectroscopy and 90 degrees light scattering. The Tt values are comparable to the melting points of the solid phosphatidic acids in the fully protonated states, but large differences exist for the charged states. The Tt vs. pH diagrams of the four phosphatidic acids are quite similar and of a characteristic shape. Increasing ionisation results in a maximum value for the transition temperatures at pH 3.5 (pK1). The regions between the first and the second pK of the phosphatidic acids are characterised by only small variations in the transition temperatures (extended plateau) in spite of the large changes occurring in the surface charge of the membranes. The slope of the plateau is very shallow with increasing ionisation. A further decrease in the H+ concentration results in an abrupt change of the transition temperature. The slope of the Tt vs. pH diagram beyond pK2 becomes very steep. This is the result of reduced hydrocarbon interaction energy, which was demonstrated by differential scanning calorimetry (Blume, A. and Eibl, H., unpublished data).

Fluorescence Polarization↗
PubMed1979

Electrostatic interactions at charged lipid membranes. Electrostatically induced tilt.

The changes in bilayer structure induced by surface charges in the case of an ionizable lipid were studied by X-ray diffraction, Raman spectroscopy, and film-balance measurements. With increasing surface charge in the ordered phase, the X-ray results show a decrease in bilayer thickness, whereas the hydrocarbon chain packing stays essentially constant, the Raman data signify that the internal chain ordering does not change, and the monolayer studies show a lateral expansion of the bilayer. These results are interpreted in terms of a tilt of the chains caused by the surface charges on the polar heads. The tilt angle between the direction of the chains and the bilayer normal is obtained by a detailed theoretical evaluation. The tilt allows for a better understanding of the electrostatically induced shift of the phase transition temperature and of the shift induced by the binding of water in the case of lecithin in contrast ethanolamine.

Hydrogen-Ion Concentration↗
PubMed1979

Motion of the lengthened zwitterionic head groups of C16-lecithin analogues in aqueous solutions as studied by dielectric relaxation measurements.

Phosphatidyl choline analogues with increased phosphate-trimethylammonium distance were synthesized and aqueous solutions of these bilayer forming phospholipids were prepared. Dielectric spectra of the solutions were measured at several temperatures around the crystalline/liquid-crystalline phase transition temperature of the samples. The observed data are treated in terms of a Debye relaxation function and also of a relaxation function based on a theoretical model of the aqueous solutions of multibilayer vesicles. As a noteworthy result, a pronounced cooperativity effect in the diffusive motions of the zwitterionic head groups emerges. The degree of cooperativity depends on the radius of curvature of the multibilayer vesicles and also on the length of the phospholipid zwitterions. The values for the mobility of the trimethylammonium group are of the same order of magnitude as those for the mobility of whole phospholipid molecules in its lateral diffusive motion. Indications for a phase transition at a temperature above the main transition temperature are found with solutions of C16- lecithin analogues with 9 and 10 methylene groups between the phosphate and the trimethylammonium group.

Journal Article↗
PubMed1978

Differential scanning calorimetry of dipalmitoyl phosphatidylcholine analogues and of their interaction products with basic polypeptides.

The thermotropic behaviour of dipalmitoyl phosphatidylcholine analogues with a varying number (n) of CH2 groups between the phosphate and the quaternary ammonium has been investigated. The temperature (Tm) and the enthalpy (deltaH) of the phase transition are non-monotonous functions of the number of CH2 groups. Tm oscillates between 40 and 45 degrees C and deltaH between 7 and 13 kcal/mol for a variation of n between 2 and 11. It is concluded that the hydrocarbon chains in the head groups do not penetrate the hydrocarbon region and do not contribute directly to the melting of the acyl chains. It is suggested that their length may affect the critical balance between the attractive and the repulsive forces within the bidimensional lattice of the head groups. Copolypeptides of lysine with phenylalanine do not appreciably affect the Tm but have a pronounced effect on deltaH of the lipid phase transition, which depends strongly on the ratio of the two amino acids in the polypeptide. The effect of copolypeptide of any defined composition on deltaH is also a non-monotonous function of the number of CH2 groups in the phosphatidylcholine head group, but it does not parallel completely the oscilations in the Tm and deltaH of the pure lipids.

Calorimetry, Differential Scanning↗
PubMed1978

The preparation of phospholipids by phospholipase D.

The transfer of the phosphatidyl residue from egg phosphatidylcholine to primary alkanols catalyzed by phospholipase D was systematically investigated. It was demonstrated that 1) the chain length of the alkanols is of critical importance, e.g. transphosphatidylation does not occur to alkanols or alkandiols with more than six carbon atoms; 2) double or triple bonds in the acceptor molecule do not influence the transfer reaction; 3) fluorine is tolerated in the acceptor molecule, but the transfer rate decreases with increasing atomic weight from chlorine to iodine. Synthetic phosphatidylcholines with large variations in the apolar part of the molecule, the phosphorylcholines of 1.2-diacyl-sn-glycerol, Acyl-propandiol-(1.3) and 1.2-cyclopentadecylmethylidene-glycerol, have been successfully used in the transfer reaction. Transesterification is an attractive route for the synthesis of phospholipids differing in the polar part of the molecule.

Egg Yolk↗
PubMed1978

Phospholipid synthesis: Oxazaphospholanes and dioxaphospholanes as intermediates.

The synthesis of phospholipids described herein allows an almost quantitative conversion of 1,2-diacylglycerols to phospholipids via cyclic intermediates such as oxazaphospholanes or dioxaphospholanes, which are the only products observed when ethanolamine or ethylene glycol is allowed to react with phosphatidic acid dichlorides. The acidic hydrolysis of the cyclic intermediates occurs rapidly without the formation of by-products and results in phospholipids differing in the structure of the polar part depending on which vicinal aminoalcohols or diols are used. For instance, phosphatidylethanolamines, -(N-methyl)ethanolamines, and -serine benzyl esters are directly formed from the corresponding oxazaphospholanes. Phosphatidyl(N,N-dimethyl)ethanolamines and -cholines are prepared by amination of the bromoethyl esters of phosphatidic acids, which can be obtained by treatment of dioxaphospholanes with sodium bromide. A similar sequence of reactions starting from 1-acyl-2-benzylglycerols or monoacylpropane-1,3-diols will result in the respective monoacyl analogues such as lysophospholipids or the so-called desoxylysophospholipids. The mild reaction conditions, good yields (>90% based on diacylglycerol), and high purity of the products make this route an attractive procedure for phospholipid synthesis; in addition, it avoids the need for chromatography and thus can be utilized on a large scale.

Journal Article↗
PubMed1977

The influence of phospholipid polar groups on gramicidin channels.

The influence of well-defined changes in the polar part of phospholipid molecules on the properties of black lipid membranes was studied using a series of phospholipids with identical hydrocarbon chains, but systematically changed polar groups. The hydrocarbon tails of the lipids under study were composed of 1,2-dipentadecylmethylidene glycerol. The polar parts differed in the degree of N-methylation and comprised phosphocholine, -N,N-dimethylethanolamine, -N-methylethanolamine and ethanolamine. Stable black lipid membranes could be formed with the solvents octane, decane, dodecane, tetradecane and hexadecane. The properties of gramicidin-induced single ionic channels changed systematically in membranes from the phosphatidylcholine to the phosphatidylethanolamine analogue, as indicated by an increase in the amplitude lambda of the unit conductance step and a decrease in the average channel life-time or duration tau. The series of tau-values was opposite to that expected from hydrocarbon thickness (specific capacitance). It is suggested that the surface tension gamma is a relevant parameter for the prediction of tau-values.

Binding Sites↗
PubMed1976

Electrostatic interactions at charged lipid membranes. I. Effects of pH and univalent cations on membrane structure.

Electrostatic interactions at charged lipid membranes make a significant contribution to the free energy of the system, and can be varied within a wide range by alteration either of the membrane's surface charge density or of the concentration of electrolytes in the surrounding medium. Changes in the charged membrane's structure, such as the ordered in equilibrium fluid phase transition, can thus be induced at constant temperature by variations in pH and salt concentration. An adequate quantitative description of these phenomena is obtained from the Gouy--Chapman theory. The good agreement between theory and experiment confirms that the expression derived for the electrostatic free energy especially in respect of its positive sign is correct. The classical expression derived for the electrostatic free energy, especially in respect of its positive sign, is correct. The classical expression for the "free energy of the double layer" derived by Verwey and Overbeek, which has a negative sign, is not applicable to lipid membranes with ionizable polar groups.

Cations, Monovalent↗
PubMed1975

1-Pyrene-butyrylcholine: a fluorescent probe for the cholinergic system.

The action of 1-pyrene-butyrylcholine, a new cholinergic fluorescent probe, has been studied at the cellular level using electrophysiological and fluorescence techniques. The spectroscopic properties of the probe were found to be similar to those pf pyrene-butyric acid, the excited-state lifetime in air-saturated aqueous solutions being 92 nsec. At micromolar concentrations the probe was found to exert a nondepolarizing, reversible blocking action at the neuromuscular junction of the frog. The same cholinolytic effect was observed in hypersensitive denervated muscles. The synaptic localization of the probe could be observed with fluorescence microscopy using sub- and micromolar concentrations. Treatment of the nerve-muscle preparations with proteolytic enzymes, resulting in the separation of the nerve ending from the muscle end-plate, enabled a distinction to be made between the fluorescence arising from these two parts of the synapse. Intense presynaptic fluorescence was observed, and was not altered by micromolar concentrations of alpha-bungarotoxin, d-tubocurarine, hemicholinium, or cholinesterase inhibitors. Faint reversible staining of the end-plate region was observed in enzymically treated muscles and was inhibited by prior treatment with alpha-bungarotoxin. Fluorescent alpha-toxin revealed similar patterns of fluorescence in the end-plate of enzyme-treated muscles. The postsynaptic localization of the fluorescent probe is therefore tentatively identified as the one producing the cholinolytic effect upon binding to acetylcholine receptor sites.

Animals↗
PubMed1974

Electrostatic effects on lipid phase transitions: membrane structure and ionic environment.

Ordered --> fluid phase transitions in bilayers of charged lipids are accompanied by a decrease in electrostatic free energy mainly as a result of bilayer expansion. For uniform charge distribution the Gouy-Chapman theory of the electrical double layer predicts a decrease of the transition temperature with increasing charge density. We studied the effects of pH and mono- and divalent cations on the phase transition of lecithin, cephalin, phosphatidylserine, and phosphatidic acid bilayers. Phosphatidic acid with two ionizable protons was selected for a systematic investigation. A change in pH from 7 to 9 increases the charge per polar group from one to two elementary charges. This lowers the transition temperature by about 20 degrees C in agreement with the theory. In this pH region rather small changes in pH suffice to induce the phase transition at constant temperature. Divalent cations (Mg(++) and Ca(++)) increase the transition temperature by charge neutralization and thus can be used to induce the fluid --> ordered transition at constant temperature. In contrast, monovalent cations (Li(+), Na(+), K(+)) lower the transition temperature, or fluidize the bilayer structure at a given temperature. Rather small changes in ionic environment can induce gross alterations in bilayer structure; divalent and monovalent cations have antagonistic effects. This result parallels current theories on nerve excitation and sensory transduction where cation-induced structural changes in biomembranes are invoked.

Calcium↗