Intervesicular phospholipid exchange. An NMR study.

Phospholipid exchange between phosphatidylinositol and phosphatidylcholine ?vesicles has been studied by NMR spectroscopy with use of hydrophilic paramagnetic lanthanide probes (Pr-3+ and Eu-3+ ions). The dependence of the lanthanide induced shifts in the1-H and 31-P NMR spectra on the phospholipid composition of the vesicles could be used for its quantitative evaluation. The method has been proved to be applicable for studying phospholipid exchange stimulated by soluble proteins (postmicrosomal supernatant fraction) from rat liver. Furthermore it has been shown that the phospholipid molecules newly introduced by protein-stimulated exchange are predominantly incorporated into the outermonolayer of the vesicular bilayer membrane. This makes it possible to produce liposomes with asymmetric distribution of the phospholipids across the bilayer.