LASER-LIGHT SCATTERING STUDY OF SIZE AND STABILITY OF GANGLIOSIDE-PHOSPHOLIPID SMALL UNILAMELLAR VESICLES

The effect of the presence of ganglioside GM1, up to 20% by mol, on the size, stability upon aging, and changes with dilution, of small unilamellar vesicles of egg phosphatidylcholine (EPC) was studied by static and dynamic laser-light scattering technique. Standardised conditions were preliminarily set up for the preparation of small unilamellar vesicles by the sonication-ultra-centrifugation method. Under these conditions the presence of ganglioside caused a progressive decrease of lipid concentration in the upper 2.2 ml of high speed supernatant, from the original 9 μmol/ml to 1.3 μmol/ml reached with vesicles containing 20% of GM1. The hydrodynamic radius (RH), apparent molecular weight (M) and polydispersity index (ν) decreased in the presence of ganglioside from the values of 16 nm, 3.3 × 106 and 0.15, respectively, to 11 nm, 1.9 × 106 and 0.10, in vesicle preparations with 20% of GM1. RH and ν of EPC vesicles increased by only 3% and 12%, respectively, upon aging at 37°C for 6 h. The variations of the same parameters in vesicles containing up to 15% of GM1 were still lower, indicating that the presence of ganglioside tends to increase the stability upon aging of small unilamellar vesicles. Dilution of vesicle dispersions down to 0.1 μmol/ml caused a modest, but significant increase of RH, M and ν. The extent of increase was similar for EPC and EPC/GM1 vesicles with a GM1 proportion lower than 20%. Passage of GM1 containing vesicles on molecular sieve chromatographic columns, caused changes of RH, M and ν, which were consistent with the dilution operated during chromatography.