Role of Water in Proton-Hydroxide Conductance Across Model and Biological Membranes

The goal of this research is to understand the mechanism of proton translocation in model and biological membranes. The significance is that electrochemical proton gradients and proton transport are central to many bioenergetic functions of cells. It is essential to address both the barrier function of membranes, and the process by which protons are directed to specific reaction sites within the membrane. The primary theme concerns the role of water in proton translocation, and particularly the possibility that hydrogen-bonded water structures contribute to the transport process. In previous studies, we have shown that proton permeability of lipid bilayers is orders of magnitude greater than that of other cations. To explain this observation, we suggested that transient hydrated defects are continuously being produced by thermal fluctuations in the lipid. If the water in the defects were associated by hydrogen bonding, protons could cross the defect by hydrogen bond exchange along the associated water molecules, accounting for the high relative permeability of protons. This concept can be extended to other membrane systems. Gramicidin A contains a 0.4 nm channel which conducts protons through hydrogen bonded water, thereby providing an important model for investigating such processes. The Fo subunit of coupling membranes has the function of directing protons to the site of ATP synthesis in the F1 ATPase. In the work planned for next year, biophysical aspects of proton transport will be studied in lipid bilayers, gramicidin channels and the Fo subunit of coupling membranes. Keywords Membranes biology Proton transport Membrane permeability.