| 1. |
- Bergmann, U, et al.
(författare)
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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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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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| 2. |
- Britt, R D, et al.
(författare)
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Recent pulsed EPR studies of the Photosystem II oxygen-evolving complex : implications as to water oxidation mechanisms
- 2004
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - Univ Calif Davis, Dept Chem, Davis, CA 95616 USA. Univ Calif Berkeley, Lawrence Berkeley Lab, Melvin Calvin Lab, Phys Biosci Div, Berkeley, CA 94720 USA. Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA. : ELSEVIER. - 0005-2728 .- 1879-2650. ; 1655:1-3, s. 158-171
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Tidskriftsartikel (refereegranskat)abstract
- The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulation (ESEEM) and electron spill echo-electron nuclear double resonance (ESE-ENDOR) are used to investigate the structure of the Photosystem II oxygen-evolving complex (OEC), including the paramagnetic manganese cluster and its immediate surroundings. Recent unpublished results from the pulsed EPR laboratory at UC-Davis are discussed, along with aspects of recent publications, with a focus on substrate and cofactor interactions. New data on the proximity of exchangeable deuterons around the Mn cluster poised in the So-state are presented and interpreted. These pulsed EPR results are used in an evaluation of several recently proposed mechanisms for PSII water oxidation. We strongly favor mechanistic models where the substrate waters bind within the OEC early in the S-state cycle. Models in which the O-O bond is formed by a nucleophilic attack by a Ca2+-bound water on a strong S-4-state electrophile provide a good match to the pulsed EPR data. (C) 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Cinco, R M, et al.
(författare)
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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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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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| 4. |
- Isgandarova, S, et al.
(författare)
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Functional differences of photosystem II from Synechococcus elongatus and spinach characterized by flash induced oxygen evolution patterns
- 2003
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Ingår i: Biochemistry. - : AMER CHEMICAL SOC. - 0006-2960 .- 1520-4995. ; 42:30, s. 8929-8938
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Tidskriftsartikel (refereegranskat)abstract
- Detailed comparative studies of flash induced oxygen evolution patterns in thylakoids from the thermophilic cyanobacterium Synechococcus elongatus (S. elongatus; also referred to as Thermosynechococcus elongatus) and from spinach led to the following results: (i) the miss parameter cc of S. elongatus thylakoids exhibits a pronounced temperature dependence with a minimum of 7% at 25 degreesC and values of 17 and 10% at 3 and 35 degreesC, respectively, while for spinach thylakoids alpha decreases continuously from 18% at 35 degreesC down to 8% at 3 degreesC; (ii) at all temperatures, the double hit probability exceeds in S. elongatus the corresponding values of spinach by an increment Deltabeta of about 3%; (iii) at 20 degreesC the slow relaxation of the oxidation states S-2 and S-3 is about 15 and 30 times, respectively, slower in S. elongatus than in spinach, while the reduction of these S states by tyrosine Y-D is 2-3 times faster; (iv) the reaction SOYDox --> S1YD is slower by a factor of 4 in S. elongatus as compared to spinach; and (v) the activation energies of S state dark relaxations in S. elongatus are all within a factor of 1.5 as compared to the previously reported values from spinach thylakoids [Vass, I., Deak, Z., and Hideg, E. (1990) Biochim. Biophys. Acta 1017, 63-69; Messinger, J., Schroder, W. P., and Renger, G. (1993) Biochemistry 32, 7658-7668], but the difference between the activation energies of the Slow S-2 and S-3 decays is significantly larger in S. elongatus than in spinach. These results are discussed in terms of differences between cyanobacteria and higher plants on the acceptor side of PSII and a shift of the redox potential of the couple Y-D/Y-D(ox). The obtained data are also suitable to address questions about effects of the redox state of Y-D on the miss probability and the possibility of an S state dependent miss parameter.
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| 5. |
- Messinger, Johannes, 1963-, et al.
(författare)
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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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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 123:32, s. 7804-7820
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Tidskriftsartikel (refereegranskat)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. |
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| 7. |
- Messinger, Johannes, 1963-
(författare)
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Evaluation of different mechanistic proposals for water oxidation in photosynthesis on the basis of Mn4OxCa structures for the catalytic site and spectroscopic data
- 2004
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - Max Planck Inst Bioinorgan Chem, D-45470 Mulheim, Germany. : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 6:20, s. 4764-4771
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress in EPR and EXAFS spectroscopy, quantum mechanical calculations and X-ray crystallography led to a tremendous improvement in our picture of the catalytic site of water oxidation in photosystem II. It is now likely that the four Mn ions are grouped in a 3 + 1 fashion with three short Mn-Mn distances of about 2.7 Angstrom and one long Mn-Mn distance of 3.3 Angstrom. In addition, Ca has been firmly localized close to the Mn centers, with an average distance of 3.4 Angstrom and an average angle of the Mn-Ca vectors close to the membrane normal (less than or equal to23degrees). The recent crystal structure of Ferreira et al. (Science, 2004, 303, 1831-1838) suggests that the Mn-3 unit and Ca form a distorted cubane like structure. The fourth Mn is 'dangling' from this unit either via a mu(4)-oxo bridge or a mono mu-oxo bridge. However, the precise Mn-Mn distances and the bridging situation still need to be worked out. On this structural basis and the available spectroscopic data two possible mechanisms for photosynthetic water oxidation are discussed in order to highlight questions that still need to be solved for a full understanding of this fascinating reaction.
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| 8. |
- Messinger, Johannes, 1963-
(författare)
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Towards understanding the chemistry of photosynthetic oxygen evolution : dynamic structural changes, redox states and substrate water binding of the Mn cluster in photosystem II
- 2000
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - Tech Univ Berlin, Max Volmer Inst, D-10623 Berlin, Germany. : ELSEVIER. - 0005-2728 .- 1879-2650. ; 1459:2-3, s. 481-488
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Tidskriftsartikel (refereegranskat)abstract
- This mini-review summarizes my postdoctoral research in the labs of T. Wydrzynski/C.B. Osmond, J.H.A. Nugent/M.C.W. Evans and V.K. Yachandra/K. Sauer/M.P. Klein. The results are reported in the context of selected data from the literature. Special emphasis is given to the mode of substrate water binding, Mn oxidation states and the structures of the Mn cluster in the four (meta)stable redox states of the oxygen evolving complex. The paper concludes with a working model for the mechanism of photosynthetic water oxidation that combines CL-oxo bridge oxidation in the S-3 State (V.K. Yachandra, K. Sauer, M.P. Klein, Chem. Rev. 96 (1996) 2927-2950) with O-O bond formation between two terminal Mn-hydroxo ligands during the S-3 --> (S-4) --> S-0 transition. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 9. |
- Robblee, J H, et al.
(författare)
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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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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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| 10. |
- Sarrou, J, et al.
(författare)
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Nitric oxide-induced formation of the S-2 state in the oxygen-evolving complex of photosystem II from Synechococcus elongatus
- 2003
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Ingår i: Biochemistry. - : AMER CHEMICAL SOC. - 0006-2960 .- 1520-4995. ; 42:4, s. 1016-1023
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Tidskriftsartikel (refereegranskat)abstract
- In spinach photosystem II (PSII) membranes, the tetranuclear manganese cluster of the oxygen-evolving complex (OEC) can be reduced by incubation with nitric oxide at -30 degreesC to a state which is characterized by an Mn-2(II, III) EPR multiline signal [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581-3587]. This state was recently assigned to the S-2 state of the OEC [Schansker, G., Goussias, C., Petrouleas, V., and Rutherford, A. W. (2002) Biochemistry 41, 3057-3064]. On the basis of EPR spectroscopy and flash-induced oxygen evolution patterns, we show that a similar reduction process takes place in PSII samples of the thermophilic cyanobacterium Synechococcus elongatus at both -30 and 0 degreesC. An EPR multiline signal, very similar but not identical to that of the S-2 state in spinach, was obtained with monomeric and dimeric PSII core complexes from S. elongatus only after incubation at -30 degreesC. The assignment of this EPR multiline signal to the S-2 state is corroborated by measurements of flash-induced oxygen evolution patterns and detailed fits using extended Kok models. The small reproducible shifts of several low-field peak positions of the S-2 EPR multiline signal in S. elongatus compared to spinach suggest that slight differences in the coordination geometry and/or the ligands of the manganese cluster exist between thermophilic cyanobacteria and higher plants.
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