Liposomal Membranes. V. Interaction of Zinc(II) Ion with Egg Phosphatidylcholine Liposomes

The efficiency of encapsulation of several divalent metal ions, mainly Zn(II) ion, into egg lecithin liposomes has been investigated with particular attention to the stability of liposomal membranes against the transition metal(II) ions. The stronger interaction of metal ions to lecithins led to the less formation of liposomes. The addition of a suitable amount of nonionic detergent, 2-[ω-hydroxypentadeca(oxyethylene)-α-yl]-1,3-bis(dodecyloxy)propane (2C1215G, see text), enhanced the encapsulation of Zn(II) and Cu(II) ions in liposomes. The stoichiometric measurement for the binding of Zn(II) ion to single compartment liposomes of egg lecithin suggested that a Zn(II) ion is interacting with three or four lecithin molecules on the average in both halves of liposomal bilayers. Even under the circumstances, the bilayer structure of liposomes was certainly kept stable, which was electron micrographically visualized.