Abstract：
:Detailed information on room-temperature structure and oxidation state of the Photosystem II (PS II) manganese complex is needed to put mechanistic considerations on solid grounds. Because previously this information had not been available, the tetranuclear manganese complex was investigated by X-ray absorption spectroscopy (XAS) on PS II membrane particles at 290 K. Due to methodical progress (collection of XAS spectra within 10 s or less), significant X-ray radiation damage can be avoided; room-temperature XAS investigations on the PS II in its native membrane environment become feasible. Thus, the ambiguity with respect to the mechanistic relevance of low-temperature XAS results is avoidable. At 290 K as well as at 18 K, the manganese complex in its dark-stable state (S(1)-state) seemingly is a Mn(III)(2)Mn(IV)(2) complex comprising two di-mu(2)-oxo bridged binuclear manganese units characterized by the same Mn-Mn distance of 2.71-2.72 A at both temperatures. Most likely, manganese oxidation states and the protonation state of the bridging oxides are fully temperature independent. Remarkably, at room-temperature manganese-ligand distances of 3.10 and 3.65 A are clearly discernible in the EXAFS spectra. The type of bridging assumed to result in Mn-Mn or Mn-Ca distances around 3.1 A is, possibly, temperature-dependent as suggested by distance lengthening upon cooling by 0.13 A. However, mechanistic proposals on photosynthetic water oxidation, which involve the dimer-of-dimers model [Yachandra, V. K., et al. (1993) Science 260, 675-679] are not invalidated by the presented results.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Meinke C,Solé VA,Pospisil P,Dau Hdoi
10.1021/bi9924258subject
Has Abstractpub_date
2000-06-20 00:00:00pages
7033-40issue
24eissn
0006-2960issn
1520-4995pii
bi9924258journal_volume
39pub_type
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