Kinetics of proton exchange of phosphatidylethanolamine in phospholipid vesicles

The rate of proton exchange of the amino protons of phosphatidylethanolamine (PE) in sonicated mixed phospholipid vesicles has been determined by NMR spectroscopy. The rate of exchange increases with increasing pH and phosphate concentration. In the absence of buffer the dominant exchange process is an intrasurface reaction in which NH2 groups react via water with NH3+ groups on the outer surface. Addition of cholesterol reduces the rate constant for intrasurface exchange. The experiments are evidence that such reactions could be dominant in proton transport in and to membrane surfaces.