Poly(aspartic acid)-dependent fusion of liposomes bearing the quaternary ammonium detergent [[[(1,1,3,3-tetramethylbutyl)cresoxy]ethoxy]ethyl] dimethylbenzylammonium hydroxide.

Addition of the quaternary ammonium detergent [[[(1,1,3,3-tetramethylbutyl)cresoxy]ethoxy]ethyl] dimethylbenzylammonium hydroxide (DEBDA[OH]) and the fluorescent probes N-(7-nitro-2-1,3-benzoxadiazol-4-yl)phosphatidylethanolamine and N-(lissamine rhodamine B sulfonyl)phosphatidylethanolamine (N-NBD-PE and N-Rh-PE, respectively) to liposomes composed of phosphatidylcholine (PC) and cholesterol (chol) resulted in the formation of fluorescently labeled liposomes bearing DEBDA[OH]. Incubation of the anionic polymer poly(aspartic acid) (PASP) with such liposomes resulted in strong agglutination, indicating an association between the negatively charged PASP and the positively charged liposome-associated DEBDA[OH]. Addition of PASP to a mixture of fluorescently labeled and nonlabeled liposomes, both carrying DEBDA[OH], resulted in a significant increase in the extent of fluorescence, namely, fluorescence dequenching. The degree of the fluorescence dequenching was dependent upon the ratio between the nonfluorescent and the fluorescent liposomes, upon the temperature of incubation, and upon the amount of DEBDA[OH] which was associated with the liposomes. Electron microscopic observations revealed that large liposomes were formed upon incubation of liposomes bearing DEBDA[OH] with PASP. The results of the present work strongly indicate that the fluorescence dequenching observed is due to a process of PASP-induced liposome-liposome fusion.