Ion Carriers and Channels in Metal-Supported Lipid Bilayers as Probes of Transmembrane and Dipole Potentials

Mercury-supported hydrophilic spacers with a lipid bilayer on top are used as biomembrane models by incorporating the ion carrier valinomycin and the ion channel melittin in the bilayer. The same films supported by gold are used to incorporate valinomycin. The extrathermodynamic absolute potential difference across the mercury/water interphase is estimated from the difference in charge density between a bare mercury electrode and a mercury electrode coated with a self-assembled dioleoylphosphatidylcholine (DOPC) monolayer. This estimate is confirmed by the potential dependence of the stationary light-on current of purple membrane fragments adsorbed at the DOPC-coated mercury electrode. The surface dipole potential of a mercury-supported self-assembled monolayer of a hydrophilic spacer is estimated from diffuse-layer effects and from the previously determined value of the absolute potential difference across the mercury/water interphase. The zero potential difference across a DOPC bilayer freely suspended ...