DC photoelectric signals from bacteriorhodopsin adsorbed on lipid monolayers and thiol/lipid bilayers supported by mercury

Purple membrane (PM) fragments were adsorbed on a dioleoylphosphatidylcholine (DOPC) monolayer and on a mixed alkanethiol/DOPC bilayer supported by mercury to investigate the kinetics of light-driven proton transport by bacteriorhodopsin (bR). The light-on and light-off capacitive currents on an alkanethiol/DOPC bilayer at pH 6.4 were interpreted on the basis of a simple equivalent circuit. The pH dependence of the biphasic decay kinetics of the light-on currents was analyzed to estimate the pKa values for the transitions releasing protons to, and taking up protons from, the solution. The linear dependence of the stationary light-on current of bR on a DOPC monolayer self-assembled on mercury upon the applied potential was interpreted on the basis of an equivalent circuit.