title: Light harvesting, energy transfer and electron cycling of a native photosynthetic membrane adsorbed onto a gold surface.
abstract: Photosynthetic membranes comprise a network of light harvesting and reaction center pigment-protein complexes responsible for the primary photoconversion reactions: light absorption, energy transfer and electron cycling. The structural organization of membranes of the purple bacterial species Rb. sphaeroides has been elucidated in most detail by means of polarized light spectroscopy and atomic force microscopy. Here we report a functional characterization of native and untreated membranes of the same species adsorbed onto a gold surface. Employing fluorescence confocal spectroscopy and light-induced electrochemistry we show that adsorbed membranes maintain their energy and electron transferring functionality. Gold-adsorbed membranes are shown to generate a steady high photocurrent of 10 microA/cm(2) for several minutes and to maintain activity for up to three days while continuously illuminated. The surface-adsorbed membranes exhibit a remarkable functionality under aerobic conditions, even when exposed to light intensities well above that of direct solar irradiation. The component at the interface of light harvesting and electron cycling, the LH1 complex, displays exceptional stability, likely contributing to the robustness of the membranes. Peripheral light harvesting LH2 complexes show a light intensity dependent decoupling from photoconversion. LH2 can act as a reversible switch at low-light, an increased emitter at medium light and photobleaches at high light.
authors.affiliation: Biophysics, Leiden University, P.O. Box 9502, 2300RA Leiden, The Netherlands.
authors.forename: Gerhard J
authors.initials: GJ
authors.lastname: Magis
authors.forename: Mart-Jan
authors.initials: MJ
authors.lastname: den Hollander
authors.forename: Willem G
authors.initials: WG
authors.lastname: Onderwaater
authors.forename: John D
authors.initials: JD
authors.lastname: Olsen
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
authors.forename: Thijs J
authors.initials: TJ
authors.lastname: Aartsma
authors.forename: Raoul N
authors.initials: RN
authors.lastname: Frese
mesh_terms: D000327:Adsorption / Q000528:radiation effects; D002462:Cell Membrane / Q000528:radiation effects* / Q000648:ultrastructure; D004566:Electrodes; D004579:Electron Transport / Q000528:radiation effects; D004735:Energy Transfer / Q000528:radiation effects*; D006046:Gold / Q000737:chemistry*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D018625:Microscopy, Atomic Force; D010788:Photosynthesis / Q000502:physiology*; D012242:Rhodobacter sphaeroides / Q000166:cytology* / Q000528:radiation effects; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013499:Surface Properties / Q000528:radiation effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D012996:Solutions; D006046:Gold