Holger Dau

..According to this hypothesis, water oxidation is facilitated by manganese reduction that is coupled to proton transfer from a substrate water to bridging oxides...

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..This specific working model may permit discussion, verification and invalidation of its various features in comparison with experimental and theoretical findings...

..Furthermore, the potential of modern XANES theory is demonstrated by presenting first simulations of the dichroism in the XANES spectra of the PSII manganese complex...

..This leads us to an extension of the classical S-state cycle towards a basic model which describes sequence and interplay of electron and proton abstraction events at the donor side of PSII [Dau and Haumann, Science 312:1471-1472, 2006]...

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..Furthermore we discuss how the I-cycle model addresses the redox-potential problem of PSII water oxidation and we propose that the accumulated bases facilitate dioxygen formation by acting as proton acceptors...

..The room temperature data is compatible with the formation of a third di-mu-oxo bridge between two Mn atoms upon the S(2)-->S(3) transition...

..In this work, first time-resolved XAS results under quasi-physiological conditions (at room temperature, non-crystalline samples) on PSII are presented. Perspectives of time-resolved BioXAS are discussed...

..Both one Fe-S cluster in HoxB and an oxygen-rich Ni coordination seem to be stabilized by RH dimerization involving the C-terminus of HoxB and by complex formation with HoxJ...

..3) Finally, the tightly-bound Mn(2)( micro -O)(2) unit is slowly reduced and released (k(3) = 0.014 min(-1))...

..It is proposed to employ controlled x-ray photoreduction in metalloprotein research for: (i) population of distinct reduced states, (ii) estimating the redox potential of buried metal centers, and (iii) research on protein dynamics...

..Oxidation-state changes are monitored with a time resolution as good as 200 micros. The current prospects and limitations as well as future perspectives of time-resolved BioXAS are discussed...

..A prominent nonthermal photothermal beam deflection signal (apparent DeltaV of about +42 A(3)) may reflect O(2) and proton release from the manganese complex, but also reorganization of the protein matrix...

..We propose that the extra quinones are located in the Q(B) cavity and serve as a PSII intrinsic pool of electron acceptors...

..It is proposed that a MnIII2(di-mu-oxo) complex is a key intermediate both in the disassembly and in the assembly reaction paths...

..The native Cl(-) ion may bind at a similar distance. Accordingly, water oxidation may not require binding of a halide directly to the metal ions of the Mn complex in its S(1) state...

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..Electrons derived from H2 cleavage, on the other hand, are transferred to NAD+ via a different pathway involving a [4Fe-4S] cluster in HoxY, which is reducible only in wild-type SH but not in the H16L variant...

..Detailed PBD studies on all S-transitions will contribute to the progress in PSII research by providing insights not accessible by other spectroscopic methods...

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..A physiological function of the recombination losses could be limitation of the lifetime of the reactive donor-side tyrosine radical (Y(.) (Z)) in the case of low-pH blockage of water oxidation...

..Implications of the structural features of the Ni site of the RH in relation to its function, hydrogen sensing, are discussed...

..eutropha...

..On these grounds, structure-activity relations are discussed...

..They also imply that, in intact organisms, the pH in the lumen compartment can hardly drop below 5, thereby limiting the ΔpH contribution to the driving force of ATP synthesis...

..The S2-state multiline EPR signal of the Mn complex was still generated in heat-treated PS II presumably lacking Ca, but retaining four Mn ions...

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..In conclusion, photosynthetic water oxidation works at high efficiency and thus can serve as both an inspiring model and a benchmark in the development of future technologies for production of solar fuels...

..Formation of a specific priming intermediate by nuclear rearrangements, setting the stage for subsequent ET, may be a common motif in reactions of biological redox cofactors...

..Our results suggest that photosynthesis at ambient conditions is not limited by product inhibition of the O(2) formation step...

..This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial...

..This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: From Natural to Artificial...

..The structure is surprisingly similar to that of an analogous Co-based film and colloidal Mn-based catalysts. Structural requirements for water oxidation are discussed...

..Kern, J., Gabdulkhakov, A., Broser, M., Zouni, A., and Saenger, W. (2009) Nat. Struct. Mol. Biol. 16, 334-342). This discovery is discussed in the context of proton transfer to the lumen...

..Assuming a QA-/QA redox potential of -0.08 V, the following redox-potential estimates are obtained: +1.25 V for P680/P680+; +1.21 V for Z/Z+ (at 10 mus); -0.42 V for Phe-/Phe; -0.58 V for P680*/P680+...

..A basic reaction-cycle model predicts an alternating proton and electron removal from the catalytic site, which facilitates energetically efficient water oxidation...

..On these grounds, mechanistic implications for the O−O bond formation chemistry are discussed. This article is part of a Special Issue entitled: Photosystem II...

..In the His237-->Ala and Cys239-->Ala mutants, coenzyme M also seemed to bind efficiently by ligation to zinc indicating that some aspects of the zinc ligand environment are surprisingly uncritical for coenzyme M binding...

..However, currently this assignment remains uncertain. In future studies, the LD-XANES analysis should play an important role in construction of unequivocal atomic-resolution model of the photosynthetic Mn complex...

..A putative role of thylakoid voltages in protection of PSII against photoinhibitory damage is discussed...

..Our results underlie the general importance of proton release at the donor side of PSII during water oxidation...

..It is proposed that the predominant coordination by (CN),O ligands stabilizes the Ni(II) oxidation state throughout the catalytic cycle and is a prerequisite for the rapid activation of the SH in the presence of oxygen...

..The data are tentatively interpreted as the stabilization of a 2-fold oxidized state of the catalytic center (S2*) with bound peroxide and its slow conversion into the normal S2 state by the release of peroxide...