Premium
A Structure‐Consistent Mechanism for Dioxygen Formation in Photosystem II
Author(s) -
Siegbahn Per E. M.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800445
Subject(s) - oxygen evolving complex , chemistry , photosystem ii , crystallography , ligand (biochemistry) , oxygen evolution , photochemistry , oxygen , electron transfer , catalytic cycle , catalysis , photosynthesis , biochemistry , receptor , organic chemistry , electrode , electrochemistry
In recent DFT studies a new mechanism for OO bond formation at the oxygen evolving center (OEC) in photosystem II has been suggested. With the structure of the S 4 state required for that mechanism, the structures of the lower S states are investigated herein by adding protons and electrons. A model was used including the full amino acids for the ones ligating the OEC, and in which the backbone positions were held fixed from the X‐ray structure. The only charged second‐shell ligand Arg357 was also included. An optimized structure for the S 1 state was reached with a large similarity to one of those suggested by EXAFS. A full catalytic cycle was derived which can rationalize the structural relaxation in the S 2 to S 3 transition, and the fact that only an electron leaves in the transition before. Water is suggested to bind to the OEC in the S 2 to S 3 , and S 4 to S 0 transitions. A new possibility for water exchange is suggested from the final energy diagram. The optimal OO bond formation occurs between an oxygen radical and an oxo ligand. The alternative mechanism, where the oxygen radical reacts with an external water, has a barrier about 20 kcal mol −1 higher.