Induction of vesicle-to-micelle transition by bile salts for DOPE vesicles incorporating immunoglobulin G.

The vesicle-to-micelle transition of immunoliposomes formed by dioleoylphosphatidyl-ethanolamine (DOPE) and palmitoyl-immunoglobulin G (p-IgG) was investigated in the presence of bile salts and conjugated bile salts. Turbidity and the release of calcein from liposomes were measured as a function of the amount of bile salts added and compared with the solubilizing profiles of the salts according to the number and configurational state of hydroxy groups in the cholate. The solubilizing phenomena by bile salts conjugated with glycine or taurine were investigated in comparison with non-conjugated bile salts. The solubilizing effect of bile salts on the bilayer of immunoliposomes increased remarkably with the number of hydroxy groups, but was not influenced by the configurational state of the hydroxy group. The half-maximal concentration of bile salts, defined as the concentration giving the half-maximum turbidity of liposome solutions, decreased with hydrophobicity in the phosphatidylcholine (PC) bilayer. The increase in the hydrophobicity of bile salts induces the ability to permeabilize and solubilize phospholipid vesicles. In the case of PC or PE liposome bilayers with inserted protein, bile salts conjugated with taurine or glycine had lower hydrophobicity than non-conjugated bile salts and showed a lower half-maximal concentration. The conjugated bile salts are believed to interact with lipids and solubilize the bilayers, while the head groups of bile salts interact with the inserted protein and extract it from the lipid bilayer.