Preparation of Liposomes. The method of liposome preparation was described in detail in a previous paper. 1 Briefly appropriate amounts of phospholipids (DMPC) were dissolved in chloroform, and then dried under a nitrogen stream. The film was kept afterwards under vacuum for 3 h to remove all traces of organic solvents. The resulting lipid film was hydrated with 10 mM HEPES buffer (100 mM NaCl, pH=7.4) in a thermostated water bath at 38 °C (above the temperature of the gel-to-liquid crystalline phase transition (T m )). The multilamellar vesicles (MLVs) thus obtained were frozen in liquid nitrogen and thawed in the water bath at ca. 10 °C above T m , and this process was repeated five times. Large unilamellar vesicles (LUVs) were obtained from the MLVs by extrusion in a 10 mL stainless steel extruder (Lipex Biomembranes, Vancouver, BC, Canada), inserted in a thermostated cell with a recirculating water bath at 38°C. The samples were passed several times through polycarbonate filters (Nucleopore,