title: Substitution of chloride by bromide modifies the low-temperature tyrosine Z oxidation in active photosystem II.
abstract: Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and functional roles in active photosystem II are still a matter of debate. We have investigated this issue by studying the effects of Cl- replacement by Br- in active PSII. In Br- substituted samples, Cl- is effectively replaced by Br- in the presence of 1.2 M NaBr under room light with protection of anaerobic atmosphere followed by dialysis. The following results have been obtained. i) The oxygen-evolving activities of the Br--PSII samples are significantly lower than that of the Cl--PSII samples; ii) The same S2 multiline EPR signals are observed in both Br- and Cl--PSII samples; iii) The amplitudes of the visible light induced S1TyrZ* and S2TyrZ* EPR signals are significantly decreased after Br- substitution; the S1TyrZ* EPR signal is up-shifted about 8G, whereas the S2TyrZ* signal is down-shifted about 12 G after Br- substitution. These results imply that the redox properties of TyrZ and spin interactions between TyrZ* and Mn-cluster could be significantly modified due to Br- substitution. It is suggested that Cl-/Br- probably coordinates to the Ca2+ ion of the Mn-cluster in active photosystem II.
authors.affiliation: Laboratory of Photochemistry, Beijing National Laboratory of Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Ren
authors.forename: Chunxi
authors.initials: C
authors.lastname: Zhang
authors.forename: Jingquan
authors.initials: J
authors.lastname: Zhao
mesh_terms: D001965:Bromides / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D001965:Bromides; D002712:Chlorides; D045332:Photosystem II Protein Complex; D014443:Tyrosine