title: Spectroscopic characterization of a semi-stable, charge-separated state in Cu(2+)-substituted reaction centers from Rhodobacter sphaeroides.
abstract: In reaction centers from Rhodobacter sphaeroides exposed to continuous illumination in the presence of an inhibitor of the Q(A)(-) to Q(B) electron transfer, a semi-stable, charge-separated state was formed with halftimes of formation and decay of several minutes. When the non-heme iron was replaced by Cu(2+), the decay of the semi-stable, charge-separated state became much slower than in centers with bound Fe(2+) with about the same rate constant for formation. In Cu(2+)-substituted reaction centers, the semi-stable state was associated with an EPR signal, significantly different from that observed after chemical reduction of the acceptor-side quinone or after illumination at low temperature, but similar to that of an isolated Cu(2+) in the absence of magnetic interaction. The EPR results, obtained with Cu(2+)-substituted reaction centers, suggest that the slow kinetics of formation and decay of the charge-separated, semi-stable state is associated with a structural rearrangement of the acceptor side and the immediate environment of the metal-binding site.
authors.affiliation: Department of Biochemistry and Biophysics, University of Göteborg, Medicinaregatan 9E, S-413 90 Göteborg, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Andréasson
authors.forename: Theres
authors.initials: T
authors.lastname: Carlsson
authors.forename: Lars Erik
authors.initials: LE
authors.lastname: Andréasson
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology / Q000528:radiation effects; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000528:radiation effects*; D011487:Protein Conformation / Q000528:radiation effects; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000528:radiation effects*; D055672:Static Electricity
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D003300:Copper