Open AccessThe Mn Cluster in the S0 State of the Oxygen-Evolving Complex of Photosystem II Studied by EXAFS Spectroscopy: Are There Three Di-μ-oxo-bridged Mn2 Moieties in the Tetranuclear Mn Complex?
Author(s) -
John H. Robblee,
Johannes Messinger,
Roehl M. Cinco,
Karen L. McFarlane,
Carmen Fernandez,
Shelly A. Pizarro,
Kenneth Sauer,
Vittal K. Yachandra
Publication year - 2002
Publication title -
journal of the american chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.115
H-Index - 612
eISSN - 1520-5126
pISSN - 0002-7863
DOI - 10.1021/ja011621a
Subject(s) - extended x ray absorption fine structure , chemistry , oxygen evolving complex , photosystem ii , cluster (spacecraft) , crystallography , oxidation state , spectroscopy , oxygen evolution , absorption spectroscopy , absorption (acoustics) , x ray absorption spectroscopy , photosynthesis , metal , electrochemistry , biochemistry , physics , organic chemistry , electrode , quantum mechanics , computer science , acoustics , programming language
A key component required for an understanding of the mechanism of the evolution of molecular oxygen by the photosynthetic oxygen-evolving complex (OEC) in photosystem II (PS II) is the knowledge of the structures of the Mn cluster in the OEC in each of its intermediate redox states, or S-states. In this paper, we report the first detailed structural characterization using Mn extended X-ray absorption fine structure (EXAFS) spectroscopy of the Mn cluster of the OEC in the S(0) state, which exists immediately after the release of molecular oxygen. On the basis of the EXAFS spectroscopic results, the most likely interpretation is that one of the di-mu-oxo-bridged Mn-Mn moieties in the OEC has increased in distance from 2.7 A in the dark-stable S(1) state to 2.85 A in the S(0) state. Furthermore, curve fitting of the distance heterogeneity present in the EXAFS data from the S(0) state leads to the intriguing possibility that three di-mu-oxo-bridged Mn-Mn moieties may exist in the OEC instead of the two di-mu-oxo-bridged Mn-Mn moieties that are widely used in proposed structural models for the OEC. This possibility is developed using novel structural models for the Mn cluster in the OEC which are consistent with the structural information available from EXAFS and the recent X-ray crystallographic structure of PS II at 3.8 A resolution.