Induction of a relatively fast transbilayer movement of phosphatidylcholine in vesicles. A 13C NMR study

$\text{N-}{}^{13}\text{CH}{}_3$] Phosphatidylcholines are introduced into the outer monolayer of phosphatidylcholine vesicles with the phosphatidylcholine exchange protein from bovine liver. The transbilayer distribution of the $\text{N-}{}^{13}\text{CH}{}_3$] phosphatidylcholine is measured with ¹³C NMR. The transbilayer movements of $\text{N-}{}^{13}\text{CH}{}_3\text{]-}\text{dioleoyl}$ phosphatidylcholine and $\text{N-}{}^{13}\text{CH}{}_3$] dimyristoyl phosphatidylcholine at 30°C in vesicles composed of these phosphatidylcholines are extremely slow processes with estimated half-times of days. $\text{N-}{}^{13}\text{CH}{}_3$] Dioleoyl phosphatidylcholine introduced into dimyristoyl phosphatidylcholine vesicles migrates from the outer to the inner monolayer with a half-time of less than 12 h. The data suggest that differential changes in the lateral packing of the two monolayers might be a driving force for transbilayer transport of phospholipids.