Structure and Interaction of Lipid Bilayers in the Presence of ATP

Even in the absence of membrane receptors, adenosine triphosphate (ATP) has been shown to interact with lipid membranes and to affect their interactions. Measurements of zeta potentials by dynamic light scattering (DLS) show that ATP creates a positive zeta potential of phosphatidylcholine (PC) lipid vesicles. A similar effect is seen on phosphatidylserine (PS) bilayers in that the negative zeta potential of PS diminishes in magnitude in the presence of ATP. We further investigate the effect of ATP on lipid bilayers by 2H NMR spectroscopy which gives us an order parameter profile for the carbon-deuterium bonds along lipid acyl chains. ATP has a measurable effect on the order parameters of both PC and PS lipids and this effect depends on temperature. We analyze the 2H NMR data using a mean-torque model that allows us to quantify the effect of ATP in terms of changes in entropy. We discuss these results in connection with the electrostatic effects observed by DLS.