X-ray spectroscopy-based structure of the Mn cluster and mechanism of photosynthetic oxygen evolution.
The mechanism by which the Mn-containing oxygen evolving complex (OEC) produces oxygen from water has been of great interest for over 40 years. This review focuses on how X-ray spectroscopy has provided important information about the structure of this Mn complex and its intermediates, or S-states, in the water oxidation cycle. X-ray absorption near-edge structure spectroscopy and high-resolution Mn Kbeta X-ray emission spectroscopy experiments have identified the oxidation states of the Mn in the OEC in each of the intermediate S-states, while extended X-ray absorption fine structure experiments have shown that 2.7 A Mn-Mn di-mu-oxo and 3.3 A Mn-Mn mono-mu-oxo motifs are present in the OEC. X-ray spectroscopy has also been used to probe the two essential cofactors in the OEC, Ca2+ and Cl-, and has shown that Ca2+ is an integral component of the OEC and is proximal to Mn. In addition, dichroism studies on oriented PS II membranes have provided angular information about the Mn-Mn and Mn-Ca vectors. Based on these X-ray spectroscopy data, refined models for the structure of the OEC and a mechanism for oxygen evolution by the OEC are presented.
Robblee
J H
JH
Melvin Calvin Laboratory, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Cinco
R M
RM
Yachandra
V K
VK
D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D014867:Water / Q000737:chemistry
D045322:Photosynthetic Reaction Center Complex Proteins; D014867:Water; D008345:Manganese; D010100:Oxygen