title: Energy and electron transfer in the photosynthetic reaction center complex of Acidiphilium rubrum containing Zn-bacteriochlorophyll a studied by femtosecond up-conversion spectroscopy.
abstract: A photosynthetic reaction center (RC) complex was isolated from a purple bacterium, Acidiphilium rubrum. The RC contains bacteriochlorophyll a containing Zn as a central metal (Zn-BChl a) and bacteriopheophytin a (BPhe a) but no Mg-BChl a. The absorption peaks of the Zn-BChl a dimer (P(Zn)), the accessory Zn-BChl a (B(Zn)), and BPhe a (H) at 4 K in the RC showed peaks at 875, 792, and 753 nm, respectively. These peaks were shorter than the corresponding peaks in Rhodobacter sphaeroides RC that has Mg-BChl a. The kinetics of fluorescence from P(Zn)(*), measured by fluorescence up-conversion, showed the rise and the major decay with time constants of 0.16 and 3.3 ps, respectively. The former represents the energy transfer from B(Zn)(*) to P(Zn), and the latter, the electron transfer from P(Zn) to H. The angle between the transition dipoles of B(Zn) and P(Zn) was estimated to be 36 degrees based on the fluorescence anisotropy. The time constants and the angle are almost equal to those in the Rb. sphaeroides RC. The high efficiency of A. rubrum RC seems to be enabled by the chemical property of Zn-BChl a and by the L168HE modification of the RC protein that modifies P(Zn).
authors.affiliation: Department of Material Science (Physics), Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Tomi
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shibata
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Seiji
authors.initials: S
authors.lastname: Taniguchi
authors.forename: Chosrowjan
authors.initials: C
authors.lastname: Haik
authors.forename: Noboru
authors.initials: N
authors.lastname: Mataga
authors.forename: Keizo
authors.initials: K
authors.lastname: Shimada
authors.forename: Shigeru
authors.initials: S
authors.lastname: Itoh
mesh_terms: D041801:Acidiphilium / Q000737:chemistry*; D025541:Bacteriochlorophyll A / Q000737:chemistry*; D004579:Electron Transport / Q000502:physiology; D005453:Fluorescence; D007700:Kinetics; D010084:Oxidation-Reduction; D010674:Pheophytins / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification*; D013057:Spectrum Analysis / Q000379:methods; D013696:Temperature; D015032:Zinc / Q000737:chemistry*
chemical_list: D025541:Bacteriochlorophyll A; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; C006678:bacteriopheophytin; D015032:Zinc