Study on size growth in the vesicle formation upon detergent removal from phospholipid/detergent mixed micelles

When 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS) was removed from the mixed CHAPS/EggPC micelles, large vesicles were prepared by dialysis or by slow step-by-step dilution, but small vesicles were prepa red by fast one-step dilution. When sodium cholate was removed from the sod ium cholate/EggPC micelles, small vesicles formed either by dialysis or by dilution; however, Ca2+ large in the presence of 5 mM Ca2+ large vesicles w ere produced by dialysis, while small vesicles were prepared by dilution. T he size growth was related to a detergent-induced fusion of the vesicles co ntaining a large amount of detergent. Using spectrophotometry, quasielastic light scattering and freeze-fracture electron microscopy the fusion events were investigated both through the process of vesicle solubilization by ad ding detergent and through the process of vesicle formation by diluting a m ixed micelle. The results suggest that a rapid CHAPS-induced fusion of the vesicles led to the large resultant vesicles and that no fusion of vesicles containing sodium cholate is responsible for the formation of small vesicl es. Furthermore, the ultimate vesicle size related to rapid or slow deterge nt removal is dependent on the kinetic aspects of the fusion.