Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 124, Issue 25, Pages 7459-7471Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja011621a
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Funding
- NIGMS NIH HHS [R01 GM055302, GM-55302, R56 GM055302] Funding Source: Medline
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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 Angstrom in the dark-stable S-1 state to 2.85 Angstrom 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 cli-y-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 Angstrom resolution.
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