Biomedical subjects

M Ollmann

Publications and source records attributed to M Ollmann.

4 recordsLinked to original sources

PubMed1988

The effect of gangliosides on the lamellar phase behaviour of phosphatidylethanolamines.

The thermotropic properties of aqueous phosphatidylethanolamine dispersions vary with hydration. Measured by EPR-spectroscopy freshly hydrated dimyristoylphosphatidylethanolamine dispersions exhibit a gel to liquid-crystalline phase transition at Tml = 48 degrees C. Dehydration could be induced by prolonged incubation of a hydrated sample at 4 degrees C. The phase transition temperature of the dehydrated phase was determined to be Tmh = 54 degrees C. From the measured phase transition curves we followed the dehydration with time and found a cooperative nucleation process. A 50% dehydration was reached after 5 days. This dehydration process could be prevented by gangliosides: 1.5 mol% of GT1b, 4 mol% of GM1 or 7 mol% of GD1a or GM3 but also 7 mol% of phosphatidic acid were able to stabilize the hydrated phase completely. The effect of gangliosides GM1, GM3, GD1a, GT1b and of the negatively charged phosphatidic acid on the phase behaviour of dimyristoylphosphatidylethanolamine (DMPE) dispersions were investigated. The phase transition temperature of freshly hydrated DMPE samples was successively decreased from 48 to 43 degrees C with increasing amounts of GD1a up to 10 mol% whereby the phase transition was significantly broadened. Gangliosides GM1, GM3 and GT1b as well as phosphatidic acid had minor effects. Dispersions of pure DMPE prepared below the transition temperature Tml form the dehydrated phase again with a melting temperature of Tmh = 54 degrees C. In the presence of 10 mol% GD1a or GT1b this value is reduced to Tml, the phase transition temperature of the hydrated phase. The reduction induced by GM3 is less pronounced. With GM1 or phosphatidic acid the samples remain partially dehydrated and the phase transition curves become biphasic up to 7 mol% ganglioside or phosphatidic acid.

Chemical Phenomena↗

PubMed1988

Minor effects of bulk viscosity on lipid translational diffusion measured by the excimer formation technique.

We have investigated the effect of bulk viscosity on lipid translational diffusion using the excimer formation technique. In contrast to a study by Vaz et al. (1987), performed with the fluorescence recovery after photobleaching technique, we observed only a minor decrease of less than a factor of two for pyrene labelled phosphatidylcholine in glycerinated phosphatidylcholine bilayer membranes compared to an aqueous dispersion. Even the diffusion of pyrene labelled gangliosides with an oligosaccharide head-group that protrudes from the membrane surface is not strongly restricted by the increased bulk viscosity. We conclude that the viscosity of the fluid bounding the lipid bilayers is of minor importance for the diffusion of membrane lipids.

Gangliosides↗

PubMed1987

Pyrene-labeled gangliosides: micelle formation in aqueous solution, lateral diffusion, and thermotropic behavior in phosphatidylcholine bilayers.

By use of the excimer technique, the formation in aqueous solution of pyrene-labeled ganglioside micelles and their lateral diffusion and distribution in phosphatidylcholine membranes were investigated. For these studies 12-(1-pyrenyl)dodecanoic acid was covalently attached to the ceramide part of lysogangliosides GM1, GM2, GM3, GD1a, and GD1b. The 12-(1-pyrenyl)dodecanoic acid substitute of phosphatidylcholine was used for comparison. All pyrene-labeled gangliosides were present in aqueous solution in a predominantly micellar form down to 2 X 10(-8) M, which is the technical limit of this method. The tendency to aggregate is highest for PyGD1a and PyGD1b. In fluid dipalmitoylphosphatidylcholine bilayers the excimer-to-monomer fluorescence intensity ratio of pyrene-labeled gangliosides PyGM1, PyGM2, PyGM3, PyGD1a, and PyGD1b increases linearly with ganglioside concentration. The calculated diffusion coefficients for gangliosides are comparable to 1.6 X 10(-7) cm2/s, which is the diffusion coefficient of pyrene-labeled phosphatidylcholine [Galla, H.-J., & Hartmann, W. (1980) Chem. Phys. Lipids 27, 199-219]. In comparison to phosphatidylcholine, the diffusion of monosialogangliosides is slightly increased, with that diffusion of disialogangliosides being slightly decreased. Ca2+ ions up to 200 mM do not affect ganglioside diffusion significantly. The shape of the lipid phase transition curves obtained by the excimer technique yields information on the lateral distribution of the tested probe molecules. Pyrene-labeled phosphatidylcholine was taken as reference for a system with complete miscibility but nonideal mixing. 1-Acyl-2-[10-(1-pyrenyl)decanoyl]-sn-glycero-3-phosphocholine (PyPC) is known to be randomly distributed in the gel and in the fluid-crystalline lipid phase of dipalmitoylphosphatidylcholine bilayer membranes. It distributes preferentially into the fluid phase in the phase-transition region. In comparison, PyPC in dimyristoylphosphatidylcholine membranes is an example of a system with nearly ideal mixing [Hresko, R. C., Sugar, J. P., Barenholz, Y., & Thompson, T. E. (1986) Biochemistry 25, 3813-3828]. Phase-transition curves of pyrene-labeled gangliosides exemplify a nearly ideal mixing system with PyGD1a or PyGD1b producing best effects. The monosialogangliosides, however, exhibit less ideality of mixing, the deviation from an ideal mixing behavior increasing with decreasing number of both neutral sugar residues and sialic acid groups. Addition of Ca2+ triggers a tightening of the phosphatidylcholine bilayer and thus induces a change in the lateral distribution of the gangliosides at the phase transition.(ABSTRACT TRUNCATED AT 400 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1985

Ganglioside headgroups decrease lipid order in reconstituted phosphatidylcholine liposomes.

The effect of oligosaccharide carrying lipids on membrane fluidity has been investigated. Gangliosides GM1 and GQ1 were reconstituted into phosphatidylcholine bilayer membranes at low concentrations (less than 5 mol%). A strong fluidizing effect was observed leading to a suppression of the phase transition temperature. This was most pronounced with highly sialylated gangliosides. Ca2+ reverses the effect due to phase separation phenomena. We assume a hydrophilic lipid-lipid interaction in accordance with previously studied glycoprotein-lipid interactions.

Animals↗