journal menu
![[Figure 4]](hi2039fig4mag.jpg)
|
|
Figure 4
Proposed structural cycle for the core of the Photosystem II manganese complex. Only the four manganese ions and the bridging oxides are depicted. In the S1 state (the dark state) and in the S2 state, two di-μ-oxo bridged binuclear manganese units (Mn—Mn distance ∼2.7 Å) are connected by a mono-μ-oxo bridge (Mn—Mn distance 3.1 Å). The S0 structure differs from the S1 structure, presumably because of the presence of a singly protonateddi-μ-oxo bridge (Mn—Mn distance ∼2.8 Å). In the S3 state the four manganese ions seem to be connected by three di-μ-oxo bridges (three Mn—Mn vectors of ∼2.7 Å); a single μ-oxo bridge might be protonated. Thus, upon the S0–S1 transition a bridging oxide is deprotonated, whereas the S2–S3 transition involves the deprotonation of a terminal oxo ligand and the formation of a new μ-oxo bridge, presumably assisted by the transformation of five-coordinated Mn(III) to six-coordinated Mn(IV) (as discussed by Dau et al., 2001  ). The changes occurring upon the manganese-oxidizing transitions of the cycle are, necessarily, reversed during the oxygen-evolving and manganese-reducing S3–(S4)–S0 transition. Putative consequences for mechanistic models of photosynthetic water oxidation are discussed elsewhere (Dau et al., 2001). |
![[Figure 4]](hi2039fig4.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
