期刊
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
卷 363, 期 1494, 页码 1237-1243出版社
ROYAL SOC
DOI: 10.1098/rstb.2007.2220
关键词
photosynthetic oxygen evolution; photosynthesis; water oxidation; X-ray absorption spectroscopy
类别
The water-oxidizing manganese complex bound to the proteins of photosystem II (PSII) was studied by X-ray absorption spectroscopy on PSII membrane particles. An extended range for collection of extended X-ray absorption fine-structure (EXAFS) data was used (up to 16.6 angstrom(-1)). The EXAFS suggests the presence of two Mn-Mn distances close to 2.7 angstrom (per Mn4Ca complex); the existence of a third Mn-Mn distance below 2.9 angstrom is at least uncertain. Interestingly, a distance of 3.7 angstrom is clearly resolved in the extended-range data and tentatively assigned to a Mn-Mn distance. Taking into account the above EXAFS results (inter alia), we present a model for the structure of the PSII manganese complex, which differs from previous atomic-resolution models. Emphasizing the hypothetical character, we propose for all semi-stable S-states: (i) a structure of the Mn4Ca(mu-O)(n) core, (ii) a model of the amino acid environment, and (iii) assignments of distinct Mn oxidation states to all the individual Mn ions. This specific working model may permit discussion, verification and invalidation of its various features in comparison with experimental and theoretical findings.
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