MODULATION BY GANGLIOSIDES OF THE LAMELLAR-INVERTED MICELLE (HEXAGONAL-II) PHASE-TRANSITION IN MIXTURES CONTAINING PHOSPHATIDYLETHANOLAMINE AND DIOLEOYLGLYCEROL

We studied the effect of gangliosides GD1a and GM1 on the lamellar-to-hexagonal II phase transition of mixtures of dioleoylphosphatidylethanolamine/dioleoydyl choline, 3:1, and of transphosphatidylated phosphatidylethanolamine with dioleoylglycerol by high-sensitivity differential scanning calorimetry, P-31-NMR, and pyrene fluorescence of a phosphatidylcholine probe. Gangliosides had a dual effect. Below 1 mol % ganglioside the hexagonal II phase transition was affected but still occurred at lower temperature than in the absence of gangliosides. The presence of between 1 and 2 mol % gangliosides increased the temperature for formation of the hexagonal II phase and progressively decreased its cooperativity. Above 3 mol % gangliosides totally inhibited the formation of both the temperature-induced and composition-induced hexagonal phase, probably by opposing the geometric distortions necessary for the inverted micellar structures.