The tetra-manganese complex of photosystem II during its redox cycle - X-ray absorption results and mechanistic implications.
Using X-ray absorption spectroscopy (XAS), relevant information on structure and oxidation state of the water-oxidizing Mn complex of photosystem II has been obtained for all four semi-stable intermediate states of its catalytic cycle. We summarize our recent XAS results and discuss their mechanistic implications. The following aspects are covered: (a) information content of X-ray spectra (pre-edge feature, edge position, extended X-ray absorption fine-structure (EXAFS), dichroism in the EXAFS of partially oriented samples); (b) S(1)-state structure; (c) X-ray edge results on oxidation state changes; (d) EXAFS results on structural changes during the S-state cycle; (e) a structural model for the Mn complex in its S(3)-state; (f) XAS-based working model for the S(2)-S(3) transition; (g) XAS-based working model for the S(0)-S(1) transition; (h) potential role of hydrogen atom abstraction by the Mn complex. Finally, we present a specific hypothesis on the mechanism of dioxygen formation during the S(3)-(S(4))-S(0) transition. According to this hypothesis, water oxidation is facilitated by manganese reduction that is coupled to proton transfer from a substrate water to bridging oxides.
Dau
H
H
Phillips-Universität Marburg, FB Biologie, Lahnberge, D-35032, Marburg, Germany. holger.dau@physik.fu-berlin.de
Iuzzolino
L
L
Dittmer
J
J
D004577:Electron Probe Microanalysis; D004578:Electron Spin Resonance Spectroscopy; D005583:Fourier Analysis; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D014867:Water / Q000737:chemistry
D009942:Organometallic Compounds; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; D010100:Oxygen