title: Location and function of the high-affinity chloride in the oxygen-evolving complex--implications from comparing studies on Cl(-)/Br(-)/I(-)-substituted photosystem II prepared using two different methods.
abstract: The high-affinity chloride ion (Cl(-)) is known to play a key role in water oxidation in photosystem II (PSII). Recent crystallographic studies revealed two Cl(-) binding sites in PSII. To examine whether these two Cl(-) ions are correlated to the high-affinity Cl(-), we prepared Cl(-)/Br(-)/I(-)-substituted PSII samples from both higher plants and cyanobacteria by using two different protocols: one was the method used in the crystallographic study (Type 1) and the other was a method developed recently to ensure the efficient replacement of Cl(-) (Type 2). While only minor effects were observed in the Type 1 preparation, efficient Br(-)/I(-)substitution by the Type 2 protocol led to significant changes in the EPR properties of the oxygen-evolving complex (OEC) and the TyrZ, as well as in oxygen-evolving activities. These results are discussed in terms of the binding site of the high-affinity Cl(-) relative to the two Cl(-) ions revealed by the recent X-ray structural data.
authors.affiliation: Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Luan
authors.initials: L
authors.lastname: Wang
authors.affiliation: Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. Electronic address: chunxizhang@iccas.ac.cn.
authors.forename: Chunxi
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jingquan
authors.initials: J
authors.lastname: Zhao
mesh_terms: D001965:Bromides / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D000458:Cyanobacteria / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D007454:Iodides / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008027:Light; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010944:Plants / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D001965:Bromides; D002712:Chlorides; D007454:Iodides; D007477:Ions; D045332:Photosystem II Protein Complex; D010100:Oxygen
keywords: Br(−)/I(−) substitution; Electron paramagnetic resonance; High-affinity chloride; Oxygen-evolving complex; Photosystem II