Outside-inside distribution and translocation of lysophosphatidylcholine in phosphatidylcholine vesicles as determinied by 13C-NMR using (N-13CH3)-enriched lipids.

1. The outside-inside distribution of palmitoyl lysophosphatidylcholine and dioleoyl phosphatidylcholine in mixed sonicated vesicles is measured with (N-13CH3)-labelled lipids using 13C NMR and Dy3+ as an impermeable shift reagent. 2. Palmitoyl lysophosphatidylcholine is preferentially localised in the outside layer of the vesicle membrane. Incorporation of cholesterol in the vesicle diminishes the extent of lysophosphatidylcholine asymmetry. 3. Palmitoyl lysophosphatidylcholine added to dioleoyl phosphatidylcholine vesicles is incorporated in the outer monolayer of the vesicle. Even after 40 h less than 2% of the lysophosphatidylcholine could be detected in the inner monolayer. Since in the cosonicated vesicles 17% of the lysophosphatidylcholine is present in the inner monolayer it can be concluded that the transmembrane movement of lysophosphatidylcholine across the lipid bilayer of these vesicles is an extremely slow process.