Bromide Does Not Bind to the Mn4Ca Complex in Its S1 State in Cl--Depleted and Br--Reconstituted Oxygen-Evolving Photosystem II: Evidence from X-ray Absorpt

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• 作者：Michael Haumann ; Marcos Barra ; Paola Loja ; Simone Lö ; scher ; Roland Krivanek ; Alexander Grundmeier ; Lars-Erik Andreasson ; Holger Dau
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：October 31, 2006
• 年：2006
• 卷：45
• 期：43
• 页码：13101 - 13107
• 全文大小：254K
• 年卷期：v.45,no.43(October 31, 2006)
• ISSN：1520-4995

文摘

Chloride is an important cofactor in photosynthetic water oxidation. It can be replaced bybromide with retention of the oxygen-evolving activity of photosystem II (PSII). Binding of bromide tothe Mn₄Ca complex of PSII in its dark-stable S₁ state was studied by X-ray absorption spectroscopy(XAS) at the Br K-edge in Cl^--depleted and Br^--substituted PSII membrane particles from spinach. TheXAS spectra exclude the presence of metal ions in the first and second coordination spheres of Br^-.EXAFS analysis provided tentative evidence of at least one metal ion, which may be manganese or calcium,at a distance of ~5 Å to Br^-. The native Cl^- ion may bind at a similar distance. Accordingly, wateroxidation may not require binding of a halide directly to the metal ions of the Mn complex in its S₁ state.