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/dioleoylphosphatidylcholine, 3:1, and of transphosphatidylated phosphatidylethanolamine with dioleoylglycerol by high- sensitivity differential scanning calorimetry, ³¹P-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.