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| 2. |
- Cinco, R M, et al.
(author)
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Orientation of calcium in the Mn4Ca cluster of the oxygen-evolving complex determined using polarized strontium EXAFS of photosystem II membranes
- 2004
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In: Biochemistry. - Univ Calif Berkeley, Lawrence Berkeley Lab, Phys Biosci Div, Melvin Calvin Lab, Berkeley, CA 94720 USA. Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA. : AMER CHEMICAL SOC. - 0006-2960 .- 1520-4995. ; 43:42, s. 13271-13282
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Journal article (peer-reviewed)abstract
- The oxygen-evolving complex of photosystem II (PS II) in green plants and algae contains a cluster of four Mn atoms in the active site, which catalyzes the photoinduced oxidation of water to dioxygen. Along with Mn, calcium and chloride ions are necessary cofactors for proper functioning of the complex. The current Study using polarized Sr EXAFS on oriented Sr-reactivated samples shows that Fourier peak II, which fits best to Mn at 3.5 Angstrom rather than lighter atoms (C, N, O, or Cl), is dichroic, with a larger magnitude at 10degrees (angle between the PS II membrane normal and the X-ray electric field vector) and a smaller magnitude at 80degrees. Analysis of the dichroism of the Sr EXAFS yields a lower and upper limit of 0degrees and 23degrees for the average angle between the Sr-Mn vectors and the membrane normal and an isotropic coordination number (number of Mn neighbors to Sr) of 1 or 2 for these layered PS II samples. The results confirm the contention that Ca (Sr) is proximal to the Mn cluster and lead to refined working models of the heteronuclear Mn4Ca cluster of the oxygen-evolving complex in PS II.
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| 5. |
- Messinger, Johannes, 1963-, et al.
(author)
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Absence of Mn-centered oxidation in the S2 → S3 Transition: : Implications for the mechanism of photosynthetic water oxidation
- 2001
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In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 123:32, s. 7804-7820
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Journal article (peer-reviewed)abstract
- A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen-evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S-3 --> [S-4] --> So transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn K beta X-ray emission spectroscopy (K beta XES) to this problem for the first time. The K beta XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S-2 --> S3 transition, in contrast to the S-0 --> S-1 and S-1 --> S-2 transitions. does not involve a Mn-centered oxidation. On the basis of new structural data from the S-3-state, manganese mu -oxo bridge radical formation is proposed for the S-2 --> S-3 transition, and three possible mechanisms for the O-O bond formation are presented.
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| 6. |
- Bergmann, U, et al.
(author)
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High-resolution X-ray spectroscopy of rare events : a different look at local structure and chemistry
- 2001
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In: Journal of Synchrotron Radiation. - Univ Calif Berkeley, Lawrence Berkeley Lab, Phys Biosci Div, Berkeley, CA 94720 USA. Univ Calif Davis, Dept Appl Sci, Davis, CA 95616 USA. CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA. : MUNKSGAARD INT PUBL LTD. - 0909-0495 .- 1600-5775. ; 8, s. 199-203
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Journal article (peer-reviewed)abstract
- The combination of large-acceptance high-resolution X-ray optics with bright synchrotron sources permits quantitative analysis of rare events such as X-ray fluorescence from very dilute systems, weak fluorescence transitions or X-ray Raman scattering. Transition-metal K beta fluorescence contains information about spin and oxidation state; examples of the characterization of the Mn oxidation states in the oxygen-evolving complex of photosystem II and Mn-consuming spores from the marine bacillus SG-1 are presented. Weaker features of the K beta spectrum resulting from valence-level and 'interatomic' ligand to metal transitions contain detailed information on the ligand-atom type, distance and orientation. Applications of this spectral region to characterize the local structure of model compounds are presented. X-ray Raman scattering (XRS) is an extremely rare event, but also represents a unique technique to obtain bulk-sensitive low-energy (<600 eV) X-ray absorption fine structure (XAFS) spectra using hard ( 10 keV) X-rays. A photon is inelastically scattered, losing part of its energy to promote an electron into an unoccupied level. In many cases, the cross section is proportional to that of the corresponding absorption process yielding the same X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) features. XRS finds application for systems that defy XAFS analysis at low energies, e.g. liquids or highly concentrated complex systems, reactive compounds and samples under extreme conditions (pressure, temperature). Recent results are discussed.
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| 7. |
- Robblee, J H, et al.
(author)
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The Mn cluster in the S0 state of the oxygen-evolving complex of photosystem II studied by EXAFS spectroscopy: : Are there three di-μ-oxo-bridged Mn2 moieties in the tetranuclear Mn complex?
- 2002
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In: Journal of the American Chemical Society. - Lawrence Berkeley Natl Lab, Phys Biosci Div, Melvin Calvin Lab, Berkeley, CA 94720 USA. Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA. : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 124:25, s. 7459-7471
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Journal article (peer-reviewed)abstract
- 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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