Leakage of sulphobromophthalein from large simple bilayer phospholipid vesicles

Single bilayer phospholipid vesicles containing entrapped sulphobromophthalein were prepared from a phospholipid film in the presence of deoxicholate at a molar ratio of deoxicholate to phospholipid of 1:2. The trapping efficiency of these vesicles was a function of sulphobromophthalein concentration during incubation, reaching a maximum at a molar ratio of egg lecithin to sulphobromophthalein of 25:1. Release of sulphobromophthalein from liposomes was observed when the vesicles were incubated with bovine serum albumin. The sulphobromophthalein released appeared to be associated with albumin when analysed by Sepharose 4B gel filtration. Leakage of sulphobromophthalein from liposomes was also observed when the vesicles were incubated with different amounts of oleic acid. However, the amount of sulphobromophthalein released from liposomes was much lower than that observed in the presence of bovine serum albumin. These vesicles incorporated up to one molecule of oleic acid for each two and a half molecules of egg lecithin, and appear to be suitable as acceptors in studies of fatty acid transfer between membranes.