title: Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature.
abstract: Electron transfer from the proximal heme c-559 to the primary donor P has been studied in reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis in which the tyrosine residue L162 was replaced by threonine. In the wild type, when the two high-potential hemes of the tetraheme cytochrome are reduced before flash excitation, a rapid electron transfer (t1/2 = 190 ns) observed at ambient temperature disappears below 190 K. In the mutant, the reaction is partly maintained down to 8 K, leading to irreversible charge separation. The reaction rate is nearly temperature-independent between 294 K and 8 K (t1/2 approximately 450 ns). The different behavior of wild type and mutant reaction centers is attributed to differences in a network of water molecules, the freezing of which may block structural reorganizations associated with cytochrome oxidation, in the wild type but not in the mutant.
authors.affiliation: Section de Bioénergétique (CNRS, URA 1290), Gif-sur-Yvette, France.
authors.forename: J M
authors.initials: JM
authors.lastname: Ortega
authors.forename: B
authors.initials: B
authors.lastname: Dohse
authors.forename: D
authors.initials: D
authors.lastname: Oesterhelt
authors.forename: P
authors.initials: P
authors.lastname: Mathis
mesh_terms: D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D007700:Kinetics; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D012241:Rhodopseudomonas / Q000378:metabolism*; D013057:Spectrum Analysis; D013696:Temperature; D013912:Threonine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D045322:Photosynthetic Reaction Center Complex Proteins; D013912:Threonine; D014443:Tyrosine