title: Lateral diffusion of ganglioside GM1 in phospholipid bilayer membranes.
abstract: The lateral diffusion coefficient of ganglioside GM1 incorporated into preformed dimyristoylphosphatidylcholine (DMPC) vesicles has been investigated under a variety of conditions using the technique of fluorescence photobleaching recovery. For these studies the fluorescent probe 5-(((2-Carbohydrazino)methyl)thio)acetyl) amino eosin was covalently attached to the periodate-oxidized sialic acid residue of ganglioside GM1. This labeled ganglioside exhibited a behavior similar to that of the intact ganglioside, and was able to bind cholera toxin. The lateral diffusion coefficient of the ganglioside was dependent upon the gel-liquid crystalline transition of DMPC. Above Tm the lateral diffusion coefficient of the ganglioside was 4.7 X 10(-9) cm2 s-1 (with greater than 80% fluorescence recovery). This diffusion coefficient is significantly slower than the one previously observed for phospholipids in DMPC bilayers. The addition of increasing amounts of ganglioside, up to a maximum of 10 mol %, did not have a significant effect on the lateral diffusion coefficient or in the percent recovery. At 30 degrees C, the lateral mobility of ganglioside GM1 was not affected by the presence of 5 mM Ca2+, suggesting that, at least above Tm, Ca2+ does not induce a major perturbation in the lateral organization of the ganglioside molecules. The addition of stoichiometric amounts of cholera toxin to samples containing either 1 or 10 mol % ganglioside GM1 produced only a small decrease in the measured diffusion coefficient. The fluorescence recovery after photobleaching experiments were complemented with excimer formation experiments using pyrene-phosphatidylcholine. Above the transition temperature the presence of 10 mol % ganglioside GMI induced a large decrease in the rate of excimer formation. These results also indicated that the addition of ganglioside GMI to phospholipid bilayer vesicles induces a significant restriction in the lateral mobility parameters of the lipid bilayer and that the presence of Ca2' does not have a further effect in the mobility of the probe molecules.
mesh_terms: D000818:Animals; D001921:Brain; D002118:Calcium; D002417:Cattle; D002772:Cholera Toxin; D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine; D005677:G(M1) Ganglioside / Q000302:isolation & purification; D007700:Kinetics; D008051:Lipid Bilayers; D008954:Models, Biological; D008968:Molecular Conformation; D011663:Pulmonary Surfactants; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014364:Tryptophan / Q000032:analysis
chemical_list: D008051:Lipid Bilayers; D011663:Pulmonary Surfactants; D005677:G(M1) Ganglioside; D014364:Tryptophan; D002772:Cholera Toxin; D002118:Calcium; D004134:Dimyristoylphosphatidylcholine