title: Blue light drives B-side electron transfer in bacterial photosynthetic reaction centers.
abstract: The core of the photosynthetic reaction center from the purple non-sulfur bacterium Rhodobacter sphaeroides is a quasi-symmetric heterodimer, providing two potential pathways for transmembrane electron transfer. Past measurements have demonstrated that only one of the two pathways (the A-side) is used to any significant extent upon excitation with red or near-infrared light. Here, it is shown that excitation with blue light into the Soret band of the reaction center gives rise to electron transfer along the alternate or B-side pathway, resulting in a charge-separated state involving the anion of the B-side bacteriopheophytin. This electron transfer is much faster than normal A-side transfer, apparently occurring within a few hundred femtoseconds. At low temperatures, the B-side charge-separated state is stable for at least 1 ns, but at room temperature, the B-side bacteriopheophytin anion is short-lived, decaying within approximately 15 ps. One possible physiological role for B-side electron transfer is photoprotection, rapidly quenching higher excited states of the reaction center.
authors.affiliation: Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, USA.
authors.forename: S
authors.initials: S
authors.lastname: Lin
authors.forename: E
authors.initials: E
authors.lastname: Katilius
authors.forename: A L
authors.initials: AL
authors.lastname: Haffa
authors.forename: A K
authors.initials: AK
authors.lastname: Taguchi
authors.forename: N W
authors.initials: NW
authors.lastname: Woodbury
mesh_terms: D001429:Bacteriochlorophylls / Q000737:chemistry / Q000378:metabolism; D002412:Cations; D004735:Energy Transfer / Q000502:physiology*; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins / Q000737:chemistry / Q000378:metabolism; D010782:Photolysis; D017785:Photons; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D001429:Bacteriochlorophylls; D002412:Cations; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; C006678:bacteriopheophytin