title: Photoelectric response of purple membrane fragments adsorbed on a lipid monolayer supported by mercury and characterization of the resulting interphase.
abstract: Purple membrane (PM) fragments were adsorbed on a dioleoylphosphatidylcholine (DOPC) monolayer supported by mercury to investigate the kinetics of light-driven proton transport by bacteriorhodopsin (bR). PM fragments were also adsorbed on a mercury-supported triethyleneoxythiol (TET) monolayer. On both monolayers, the light-on current exhibits a finite, potential dependent stationary component that decreases linearly with a positive shift in the applied potential. The light-on and light-off capacitive photocurrents were interpreted on the basis of a simple equivalent circuit, which accounts for the potential dependence of the stationary light-on current. The potential of zero stationary current is about equal to +0.010 V vs. saturated calomel electrode (SCE) on DOPC-coated mercury. The absolute potential difference across the PM fragments adsorbed at this applied potential was estimated on the basis of extrathermodynamic considerations and amounts to about +260 mV; it compares favorably with the value, +250 mV, of the transmembrane potential of zero stationary current across an oocyte plasma membrane incorporating bR [Biophys. J. 74 (1998) 403.]. The effect of the proton pumping activity of photoexcited PM fragments on the electroreduction kinetics of ubiquinone-10 incorporated in the DOPC monolayer underlying the PM fragments was investigated.
authors.affiliation: Department of Chemistry, Polo Scientifico, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Dolfi
authors.forename: Giovanni
authors.initials: G
authors.lastname: Aloisi
authors.forename: Rolando
authors.initials: R
authors.lastname: Guidelli
mesh_terms: D000327:Adsorption; D001436:Bacteriorhodopsins / Q000378:metabolism* / Q000528:radiation effects*; D025802:Electric Capacitance; D008027:Light; D008564:Membrane Potentials / Q000528:radiation effects; D008567:Membranes, Artificial; D008628:Mercury; D010713:Phosphatidylcholines / Q000737:chemistry; D010777:Photochemistry / Q000295:instrumentation / Q000379:methods; D018717:Purple Membrane / Q000378:metabolism* / Q000528:radiation effects; D012680:Sensitivity and Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D013438:Sulfhydryl Compounds; D001436:Bacteriorhodopsins; C017251:1,2-oleoylphosphatidylcholine; D008628:Mercury