The effect of gangliosides on the lamellar phase behaviour of phosphatidylethanolamines

Abstract

The thermotropic properties of aqueous phosphatidylethanolamine dispersions vary with hydration. Measured by EPR-spectroscopy freshly hydrated dimyristoylphosphatidylethanolamine dispersions exhibit a gel to liquid-crystalline phase transition at T ml = 48°C. Dehydration could be induced by prolonged incubation of a hydrated sample at 4°C. The phase transition temperature of the dehydrated phase was determined to be T mh = 54°C. From the measured phase transition curves we followed the dehydration with time and found a cooperative nucleation process. A 50% dehydration was reached after 5 days. This dehydration process could be prevented by gangliosides: 1.5 mol% of G T1b, 4 mol% of G M1 or 7 mol% of G D1a or G M3 but also 7 mol% of phosphatidic acid were able to stabilize the hydrated phase completely. The effect of gangliosides G M1, G M3, G D1a, G T1b and of the negatively charged phosphatidic acid on the phase behaviour of dimyristoylphosphatidylethanolamine (DMPE) dispersions were investigated. The phase transition temperature of freshly hydrated DMPE samples was successively decreased from 48 to 43°C with increasing amounts of G D1a up to 10 mol% whereby the phase transition was significantly broadened. Gangliosides G M1, G M3 and G T1b as well as phosphatidic acid had minor effects. Dispersions of pure DMPE prepared below the transition temperature T ml form the dehydrated phase again with a melting temperature of T mh = 54°C. In the presence of 10 mol% G D1a or G T1b this value is reduced to T ml , the phase transition temperature of the hydrated phase. The reduction induced by G M3 is less pronounced. With G M1 or phosphatidic acid the samples remain partially dehydrated and the phase transition curves become biphasic up to 7 mol% ganglioside or phosphatidic acid.