DISCUSSION OF THE STRUCTURAL AND OXIDATION STATE CHANGES OF THE Mn_4Ca COMPLEX OF PHOTOSYSTEM II ON BASIS OF RECENT X-RAY ABSORPTION RESULTS

摘要

To unravel the intricate mechanism of photosynthetic water oxidation at the Mn_4Ca complex of PSII, it is of obvious importance to characterize and understand the structural and oxidation state changes associated with the various S-state transitions of the water-oxidation cycle. Results we obtained by analysis of XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine-structure) spectra collected at the Mn K-edge are briefly summarized in Table 1; details and related results are reported elsewhere (Dau et al 2001, 2003, 2004b, Haumann et al 2002, 2004, luzzolino et al 1998, Pospisil et al 2003, Schiller et al 1998). In the present article, the XAFS results are discussed with special focus on the changes in the Mn-Mn bridging mode and the coupling of the individual S-state transitions to the protonation state of Mn ligands.