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

We studied the effect of gangliosides GD1a and GM1 on the lamellar-to- hexagonal II phase transition of mixtures of dioleoylphosphatidylethan olamine/dioleoydyl choline, 3:1, and of transphosphatidylated phosphat idylethanolamine with dioleoylglycerol by high-sensitivity differentia l scanning calorimetry, P-31-NMR, and pyrene fluorescence of a phospha tidylcholine probe. Gangliosides had a dual effect. Below 1 mol % gang lioside the hexagonal II phase transition was affected but still occur red at lower temperature than in the absence of gangliosides. The pres ence of between 1 and 2 mol % gangliosides increased the temperature f or formation of the hexagonal II phase and progressively decreased its cooperativity. Above 3 mol % gangliosides totally inhibited the forma tion of both the temperature-induced and composition-induced hexagonal phase, probably by opposing the geometric distortions necessary for t he inverted micellar structures.