title: Photosystem I complexes associated with fucoxanthin-chlorophyll-binding proteins from a marine centric diatom, Chaetoceros gracilis.
abstract: Diatoms occupy a key position as a primary producer in the global aquatic ecosystem. We developed methods to isolate highly intact thylakoid membranes and the photosystem I (PS I) complex from a marine centric diatom, Chaetoceros gracilis. The PS I reaction center (RC) was purified as a super complex with light-harvesting fucoxanthin-chlorophyll (Chl)-binding proteins (FCP). The super complex contained 224 Chl a, 22 Chl c, and 55 fucoxanthin molecules per RC. The apparent molecular mass of the purified FCP-PS I super complex (approximately 1000 kDa) indicated that the super complex was composed of a monomer of the PS I RC complex and about 25 copies of FCP. The complex contained menaquinone-4 as the secondary electron acceptor A1 instead of phylloquinone. Time-resolved fluorescence emission spectra at 77 K indicated that fast (16 ps) energy transfer from a Chl a band at 685 nm on FCP to Chls on the PS I RC complex occurs. The ratio of fucoxanthin to Chl a on the PS I-bound FCP was lower than that of weakly bound FCP, suggesting that PS I-bound FCP specifically functions as the mediator of energy transfer between weakly bound FCPs and the PS I RC.
authors.affiliation: Graduate School of Life Science, University of Hyogo, Harima Science Garden City, Hyogo 678-1297, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Masayuki
authors.initials: M
authors.lastname: Komura
authors.forename: Mai
authors.initials: M
authors.lastname: Watanabe
authors.forename: Chie
authors.initials: C
authors.lastname: Minami
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Koike
authors.forename: Shigeru
authors.initials: S
authors.lastname: Itoh
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kashino
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Satoh
mesh_terms: D002458:Cell Fractionation; D017377:Diatoms / Q000737:chemistry; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D020524:Thylakoids / Q000737:chemistry
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; C088752:fucoxanthin-, chlorophyll a-c-containing protein