Fundamental Investigation of Vesicle Bilayer Membrane Dynamics

Abstract

We studied the bilayer of vesicles from dimyristolyphosphatidylcholine (DMPC), using nitrobenzoxadiazole (NBD) probes, attached to the head (NBD-PE) and the tail (NBD-PC) of phospholipid derivatives. We characterized the bilayer as it underwent reversible transition from the gel to the fluid through a phase transition range. The main phase transition was characterized by steady state and timeresolved fluorescence anisotropy, fluorescence intensity decrement and kinetics of dithionite reduction. We also studied DMPC with dihydrocholesterol. Differences between the surface and interior regions of the bilayer region were obtained. The activation barrier was enthalpic in the gel, entropic in the fluid phase and anomalous at the transition region. In addition, the rate coefficient of NBD PC was higher than the NBD PE. The studies have developed rapid preparation method for generating giant vesicles from phosphatidylcholines. The studies show for the first time that the dithionite reduction of the NBD involves a pre-equilibrium association step based on Eyring kinetic model.