title: Excitation energy trapping and dissipation by Ni-substituted bacteriochlorophyll a in reconstituted LH1 complexes from Rhodospirillum rubrum.
abstract: Bacteriochlorophyll a with Ni(2+) replacing the central Mg(2+) ion was used as an ultrafast excitation energy dissipation center in reconstituted bacterial LH1 complexes. B870, a carotenoid-less LH1 complex, and B880, an LH1 complex containing spheroidene, were obtained via reconstitution from the subunits isolated from chromatophores of Rhodospirillum rubrum . Ni-substituted bacteriochlorophyll a added to the reconstitution mixture partially substituted the native pigment in both forms of LH1. The excited-state dynamics of the reconstituted LH1 complexes were probed by femtosecond pump-probe transient absorption spectroscopy in the visible and near-infrared spectral region. Spheroidene-binding B880 containing no excitation dissipation centers displayed complex dynamics in the time range of 0.1-10 ps, reflecting internal conversion and intersystem crossing in the carotenoid, exciton relaxation in BChl complement, and energy transfer from carotenoid to the latter. In B870, some aggregation-induced excitation energy quenching was present. The binding of Ni-BChl a to both B870 and B880 resulted in strong quenching of the excited states with main deexcitation lifetime of ca. 2 ps. The LH1 excited-state lifetime could be modeled with an intrinsic decay time constant in Ni-substituted bacteriochlorophyll a of 160 fs. The presence of carotenoid in LH1 did not influence the kinetics of energy trapping by Ni-BChl unless the carotenoid was directly excited, in which case the kinetics was limited by a slower carotenoid S1 to bacteriochlorophyll energy transfer.
authors.affiliation: Biological Research Centre, Hungarian Academy of Sciences , Temesvári krt. 62, 6726 Szeged, Hungary.
authors.forename: Petar H
authors.initials: PH
authors.lastname: Lambrev
authors.forename: Yuliya
authors.initials: Y
authors.lastname: Miloslavina
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: van Stokkum
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Stahl
authors.forename: Maciej
authors.initials: M
authors.lastname: Michalik
authors.forename: Anna
authors.initials: A
authors.lastname: Susz
authors.forename: Jędrzej
authors.initials: J
authors.lastname: Tworzydło
authors.forename: Joanna
authors.initials: J
authors.lastname: Fiedor
authors.forename: Gabriella
authors.initials: G
authors.lastname: Huhn
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Groot
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
authors.forename: Győző
authors.initials: G
authors.lastname: Garab
authors.forename: Leszek
authors.initials: L
authors.lastname: Fiedor
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D025541:Bacteriochlorophyll A / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry; D004735:Energy Transfer; D007477:Ions / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D018625:Microscopy, Atomic Force; D009532:Nickel / Q000737:chemistry*; D011521:Protochlorophyllide / Q000737:chemistry / Q000378:metabolism; D012247:Rhodospirillum rubrum / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; D007477:Ions; D045342:Light-Harvesting Protein Complexes; C001348:holochrome protein, Rhodospirillum rubrum; C005637:spheroidene; D011521:Protochlorophyllide; D002338:Carotenoids; D009532:Nickel