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 absorption spectroscopy at the Br K-edge.
Chloride is an important cofactor in photosynthetic water oxidation. It can be replaced by bromide with retention of the oxygen-evolving activity of photosystem II (PSII). Binding of bromide to the Mn(4)Ca complex of PSII in its dark-stable S(1) 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. The XAS 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 approximately 5 A to Br(-). The native Cl(-) ion may bind at a similar distance. Accordingly, water oxidation may not require binding of a halide directly to the metal ions of the Mn complex in its S(1) state.
Haumann
Michael
M
Freie Universität Berlin, FB Physik, Arnimallee 14, D-14195 Berlin, Germany.
Barra
Marcos
M
Loja
Paola
P
Löscher
Simone
S
Krivanek
Roland
R
Grundmeier
Alexander
A
Andreasson
Lars-Erik
LE
Dau
Holger
H
D001965:Bromides / Q000378:metabolism*; D005583:Fourier Analysis; D008345:Manganese / Q000378:metabolism*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D018724:Spinacia oleracea / Q000378:metabolism; D014867:Water / Q000378:metabolism
D001965:Bromides; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D014867:Water; D008345:Manganese