title: Studies on photosynthetic oxygen-evolving complex by means of Fourier transform infrared spectroscopy: calcium and chloride cofactors.
abstract: Structural roles of functional Ca2+ and Cl- ions in photosynthetic oxygen-evolving complexes (OEC) were studied using low- (640-350 cm-1) and mid- (1800-1200 cm-1) frequency S2/S1 Fourier transform infrared (FTIR) difference spectroscopy. Studies using highly active Photosystem (PS) II core particles from spinach enabled the detection of subtle spectral changes. Ca2+-depleted and Ca2+-reconstituted particles produced very similar mid- and low-frequency spectra. The mid-frequency spectrum was not affected by reconstitution with 44Ca isotope. In contrast, Sr2+-substituted particles showed unique spectral changes in the low-frequency Mn-O-Mn mode at 606 cm-1 as well as in the mid-frequency carboxylate stretching modes. The mid-frequency spectrum of Cl- -depleted OEC exhibited marked changes in the carboxylate stretching modes and the suppression of protein modes compared with that of Cl- -reconstituted OEC. However, Cl- -depletion did not exert significant effects on the low-frequency spectrum.
authors.affiliation: Laboratory for Photo-Biology (1), RIKEN Photodynamics Research Center, 519-1399 Aoba, Aramaki, Aoba, Sendai 980-0845, Japan. ykimura@postman.riken.go.jp
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Kimura
authors.forename: Koji
authors.initials: K
authors.lastname: Hasegawa
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Yamanari
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Ono
mesh_terms: D002118:Calcium / Q000172:deficiency / Q000378:metabolism* / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism* / Q000494:pharmacology; D004735:Energy Transfer; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism
chemical_list: D002712:Chlorides; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D010100:Oxygen; D002118:Calcium