COMPONENT ANALYSIS OF THE FAST PHOTOELECTRIC SIGNAL FROM MODEL BACTERIORHODOPSIN MEMBRANES - V - EFFECTS OF CHLORIDE-ION TRANSPORT BLOCKERSAND DIVALENT-CATION CHELATORS

Bacteriorhodopsin (BR), the light-driven proton pump found in Halobact eria salinarium, exhibits a fast photoelectric signal which is the man ifestation of light-induced vectorial charge separation and recombinat ion in the purple membrane. The photosignal can be decomposed into thr ee components (B1, B2, and B2'). We have associated these components w ith chemical processes taking place at various domains of bacteriorhod opsin (B1 from hydrophobic regions, and B2 and B2' from the intracellu lar and extracellular hydrophilic domains, respectively). In this repo rt, we investigate the effect of halide ions and divalent cations on t he B1 and the B2 components. We found that halide ions are required fo r the generation of the B2 component at low pH whereas divalent cation s enhance the B2 component at medium to high pH. In addition, these si gnals can be either abolished or inhibited by blockers of chloride ion transport and by divalent cation chelators, respectively. We tentativ ely decompose the B2 component into two subcomponents: B2-a for the Cl --dependent subcomponent that appears at low pH, and B2-c for the diva lent cation-sensitive subcomponent that appears at medium to high pH. It is possible that the B2-a component may be generated by interfacial Cl- transfer whereas the B2-c component may be generated by interfaci al proton transfer. (C) 1998 Elsevier Science S.A. All rights reserved .