The effects of Bile salts (BS) on the stability of dioleoylphosphatidylethanolamine (DOPE) lipo somes were investigated, observing light absorbance of vacant liposome and calcein release from entrapped lipo some. Unilamellar liposomes were prepared by using a small quantity of palmitoyl-immunoglobulin G(IgG) ($2.5\times10^{-4}$ mol/lipid mol) to stabilize the bilayer phase of the unsaturated DOPE which by itself does not form stable liposomes. The destabilization of PE immunoliposomes by papain, clearly demonstrates that the IgG is essential for stabilization of PE bilayer.
Approximately 4% of the entrapped calcein was released from the PE liposomes after 1 hr from liposome formation. Absorbance of liposomes decreased depending on the BS/lipid ratio because of the solubilization of lipid molecule in bilayer and the formation of mixed micelles. At very low BS concentrations, BS/lipid aggregates are formed in the outer vesicles monolayer, while at increasing BS concentrations, mixed micelles are formed. Cholate and its conjugates as 3$\alpha$, 7$\alpha$, 12$\alpha$-trihydroxy BS induce half-maximal solubilization of immunoliposome at approximately 2.5-, or 5-fold concentration of the 3$\alpha$, 12$\alpha$-dihydroxy BS. Conjugation of BS with glycine or taurine results in a slight enhancement of their capacity to perturb membranes.
