Effect of the phase transition on the transbilayer movement of dimyristoyl phosphatidylcholine in unilamellar vesicles

Abstract Dimyristoyl phosphatidylcholine rapidly exchanges between vesicles at 37°C without vesicle fusion. The rate of the transbilayer movement of dimyristoyl phosphatidylcholine in sonicated vesicles has been measured employing 13 C NMR using N- 13 CH 3− labeled lipids which are introduced into the outer monolayer of non-labeled vesicles by a phosphatidylcholine exchange protein. The rate of transbilayer movement of dimyristoyl phosphatidylcholine shows a distinct maximum (halftime 4 h) in the temperature range at which the hydrocarbon phase transition occurs. The activation energy of the flip-flop rate above the phase transition is 23.7 ± 2.0 kcal/mol.