| 1. |
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| 2. |
- Clausen, J, et al.
(författare)
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Evidence that bicarbonate is not the substrate in photosynthetic oxygen evolution
- 2005
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Ingår i: Plant Physiology. - : AMER SOC PLANT BIOLOGISTS. - 0032-0889 .- 1532-2548. ; 139:3, s. 1444-1450
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Tidskriftsartikel (refereegranskat)abstract
- It is widely accepted that the oxygen produced by photosystem II of cyanobacteria, algae, and plants is derived from water. Earlier proposals that bicarbonate may serve as substrate or catalytic intermediate are almost forgotten, though not rigorously disproved. These latter proposals imply that CO2 is an intermediate product of oxygen production in addition to O-2. In this work, we investigated this possible role of exchangeable HCO3- in oxygen evolution in two independent ways. (1) We studied a possible product inhibition of the electron transfer into the catalytic Mn4Ca complex during the oxygen-evolving reaction by greatly increasing the pressure of CO2. This was monitored by absorption transients in the near UV. We found that a 3,000-fold increase of the CO2 pressure over ambient conditions did not affect the UV transient, whereas the S-3 -> S-4 -> S-0 transition was half-inhibited by raising the O-2 pressure only 10-fold over ambient, as previously established. (2) The flash-induced O-2 and CO2 production by photosystem II was followed simultaneously with membrane inlet mass spectrometry under approximately 15% H-2 O-18 enrichment. Light flashes that revealed the known oscillatory O-2 release failed to produce any oscillatory CO2 signal. Both types of results exclude that exchangeable bicarbonate is the substrate for (and CO2 an intermediate product of) oxygen evolution by photosynthesis. The possibility that a tightly bound carbonate or bicarbonate is a cofactor of photosynthetic water oxidation has remained.
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| 3. |
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| 4. |
- Kulik, L, et al.
(författare)
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Pulse EPR, 55Mn-ENDOR and ELDOR-detected NMR of the S2-state of the oxygen evolving complex in Photosystem II
- 2005
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Ingår i: Photosynthesis Research. - : SPRINGER. - 0166-8595 .- 1573-5079. ; 84:1-3, s. 347-353
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Tidskriftsartikel (refereegranskat)abstract
- Pulse EPR, Mn-55-ENDOR and ELDOR-detected NMR experiments were performed on the S-2-state of the oxygen-evolving complex from spinach Photosystem II. The novel technique of random acquisition in ENDOR was used to suppress heating artefacts. Our data unambiguously shows that four Mn ions have significant hyperfine coupling constants. Numerical simulation of the Mn-55-ENDOR spectrum allowed the determination of the principal values of the hyperfine interaction tensors for all four Mn ions of the oxygen-evolving complex. The results of our Mn-55-ENDOR experiments are in good agreement with previously published data [Peloquin JM et al. (2000) J Am Chem Soc 122: 10926-10942]. For the first time ELDOR-detected NMR was applied to the S-2-state and revealed a broad peak that can be simulated numerically with the same parameters that were used for the simulation of the Mn-55-ENDOR spectrum. This provides strong independent support for the assigned hyperfine parameters.
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| 5. |
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| 6. |
- Kulik, L V, et al.
(författare)
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Electron spin-lattice relaxation of the so state of the oxygen-evolving complex in photosystem II and of dinuclear manganese model complexes
- 2005
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Ingår i: Biochemistry. - : AMER CHEMICAL SOC. - 0006-2960 .- 1520-4995. ; 44:26, s. 9368-9374
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the electron spin-lattice relaxation time T, was measured for the So state of the oxygen-evolving complex (OEC) in photosystem II and for two dinuclear manganese model complexes by pulse EPR using the inversion-recovery method. For [Mn(III)Mn(IV)(mu-O)(2)bipy(4)]ClO4, the Raman relaxation process dominates at temperatures below 50 K. In contrast, Orbach type relaxation was found for [Mn(II)Mn(III)(mu-OH)(mu-piv)(2)(Me(3)tacn)(2)](ClO4)(2) between 4.3 and 9 K. For the latter complex, an energy separation of 24.7-28.0 cm(-1) between the ground and the first excited electronic state was determined. In the So state of photosystem II, the T-1 relaxation times were measured in the range of 4.3-6.5 K. A comparison with the relaxation data (rate and pre-exponential factor) of the two model complexes and of the S-2 state of photosystem II indicates that the Orbach relaxation process is dominant for the So state and that its first excited state lies 21.7 +/- 0.4 cm(-1) above its ground state. The results are discussed with respect to the structure of the OEC in photosystem II.
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| 7. |
- Kulik, Leonid V., et al.
(författare)
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Electronic structure of the Mn4OxCa cluster in the S0 and S2 states of the oxygen-evolving complex of photosystem II based on pulse 55Mn-ENDOR and EPR Spectroscopy
- 2007
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 129:44, s. 13421-13435
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Tidskriftsartikel (refereegranskat)abstract
- The heart of the oxygen-evolving complex (OEC) of photosystem II is a Mn4OxCa cluster that cycles through five different oxidation states (S-0 to S-4) during the light-driven water-splitting reaction cycle. In this study we interpret the recently obtained Mn-55 hyperfine coupling constants of the S-0 and S-2 states of the OEC [Kulik et al. J. Am. Chem. Soc. 2005, 127, 2392-2393] on the basis of Y-shaped spin-coupling schemes with up to four nonzero exchange coupling constants, J. This analysis rules out the presence of one or more Mn(II) ions in S-0 in methanol (3%) containing samples and thereby establishes that the oxidation states of the manganese ions in S-0 and S-2 are, at 4 K, Mn-4(III, III, III, IV) and Mn-4(III, IV, IV, IV), respectively. By applying a "structure filter" that is based on the recently reported single-crystal EXAFS data on the Mn4OxCa cluster [Yano et al. Science 2006, 314, 821-825] we (i) show that this new structural model is fully consistent with EPR and Mn-55-ENDOR data, (ii) assign the Mn oxidation states to the individual Mn ions, and (iii) propose that the known shortening of one 2.85 angstrom Mn-Mn distance in S-0 to 2.75 angstrom in S-1 [Robblee et al. J. Am. Chem. Soc. 2002, 124, 7459-7471] corresponds to a deprotonation of a mu-hydroxo bridge between Mn-A and Mn-B, i.e., between the outer Mn and its neighboring Mn of the mu(3)-oxo bridged moiety of the cluster. We summarize our results in a molecular model for the S-0 -> S-1 and S-1 -> S-2 transitions.
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| 8. |
- Noering, Birgit, et al.
(författare)
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Effects of methanol on the Si-state transitions in photosynthetic water-splitting
- 2008
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Ingår i: Photosynthesis Research. - : SPRINGER. - 0166-8595 .- 1573-5079. ; 98:1-3, s. 251-260
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Tidskriftsartikel (refereegranskat)abstract
- From a chemical point of view methanol is one of the closest analogues of water. Consistent with this idea EPR spectroscopy studies have shown that methanol binds at-or at least very close to-the Mn4OxCa cluster of photosystem II (PSII). In contrast, Clark-type oxygen rate measurements demonstrate that the O-2 evolving activity of PSII is surprisingly unaffected by methanol concentrations of up to 10%. Here we study for the first time in detail the effect of methanol on photosynthetic water-splitting by employing a Joliot-type bare platinum electrode. We demonstrate a linear dependence of the miss parameter for Si state advancement on the methanol concentrations in the range of 0-10% (v/v). This finding is consistent with the idea that methanol binds in PSII with similar affinity as water to one or both substrate binding sites at the Mn(4)OxCa cluster. The possibility is discussed that the two substrate water molecules bind at different stages of the cycle, one during the S-4 -> S-0 and the other during the S-2 -> S-3 transition.
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| 9. |
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| 10. |
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| 11. |
- Pecoraro, V., et al.
(författare)
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Water oxidation chemistry of photosystem II - Discussion
- 2008
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : ROYAL SOC. - 0962-8436 .- 1471-2970. ; 363:1494, s. 1218-1219
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 12. |
- Pushkar, Yulia, et al.
(författare)
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Structure and orientation of the Mn4Ca cluster in plant photosystem II membranes studied by polarized range-extended X-ray absorption spectroscopy
- 2007
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Ingår i: Journal of Biological Chemistry. - : AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC. - 0021-9258 .- 1083-351X. ; 282:10, s. 7198-7208
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy has provided important insights into the structure and function of the Mn4Ca cluster in the oxygen-evolving complex of Photosystem II (PS II). The range of manganese extended x-ray absorption fine structure data collected from PS II until now has been, however, limited by the presence of iron in PS II. Using a crystal spectrometer with high energy resolution to detect solely the manganese K alpha fluorescence, we are able to extend the extended x-ray absorption fine structure range beyond the onset of the iron absorption edge. This results in improvement in resolution of the manganese-backscatterer distances in PS II from 0.14 to 0.09 angstrom. The high resolution data obtained from oriented spinach PS II membranes in the S-1 state show that there are three di-mu-oxo-bridged manganese-manganese distances of similar to 2.7 and similar to 2.8 angstrom in a 2:1 ratio and that these three manganese-manganese vectors are aligned at an average orientation of similar to 60 degrees relative to the membrane normal. Furthermore, we are able to observe the separation of the Fourier peaks corresponding to the similar to 3.2 angstrom manganese-manganese and the similar to 3.4 angstrom manganese-calcium interactions in oriented PS II samples and determine their orientation relative to the membrane normal. The average of the manganese-calcium vectors at similar to 3.4 angstrom is aligned along the membrane normal, while the similar to 3.2 angstrom manganese-manganese vector is oriented near the membrane plane. A comparison of this structural information with the proposed Mn4Ca cluster models based on spectroscopic and diffraction data provides input for refining and selecting among these models.
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| 13. |
- Shevela, Dmitriy, et al.
(författare)
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Characterization of the water oxidizing complex of photosystem II of the Chl d-containing cyanobacterium Acaryochloris marina via its reactivity towards endogenous electron donors and acceptors
- 2006
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 8:29, s. 3460-3466
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Tidskriftsartikel (refereegranskat)abstract
- Acaroychloris (A.) marina is a unique oxygen evolving organism that contains a large amount of chlorophyll d (Chl d) and only very few Chl a molecules. This feature raises questions on the nature of the photoactive pigment, which supports light-induced oxidative water splitting in Photosystem II (PS II). In this study, flash-induced oxygen evolution patterns (FIOPs) were measured to address the question whether the Si state transition probabilities and/or the redox-potentials of the water oxidizing complex (WOC) in its different Si states are altered in A. marina cells compared to that of spinach thylakoids. The analysis of the obtained data within the framework of different versions of the Kok model reveals that in light activated A. marina cells the miss probability is similar compared to spinach thylakoids. This finding indicates that the redox-potentials and kinetics within the WOC, of the reaction center (P680) and of Y-Z are virtually the same for both organisms. This conclusion is strongly supported by lifetime measurements of the S-2 and S-3 states. Virtually identical time constants were obtained for the slow phase of deactivation. Kinetic differences in the fast phase of S-2 and S-3 decay between A. marina cells and spinach thylakoids reflect a shift of the E-m of Y-D/Y-D(OX) to lower values in the former compared to the latter organisms, as revealed by the observation of an opposite change in the kinetics of S-0 oxidation to S-1 by Y-D(OX). A slightly increased double hit probability in A. marina cells is indicative of a faster Q(A)(-) to Q(B) electron transfer in these cells compared to spinach thylakoids.
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| 14. |
- Shevela, Dmitriy, et al.
(författare)
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Hydrogencarbonate is not a tightly bound constituent of the water-oxidizing complex in photosystem II
- 2008
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : ELSEVIER. - 0005-2728 .- 1879-2650. ; 1777:6, s. 532-539
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Tidskriftsartikel (refereegranskat)abstract
- Since the end of the 1950s hydrogencarbonate ('bicarbonate') is discussed as a possible cofactor of photosynthetic water-splitting, and in a recent X-ray crystallography model of photosystem II (PSII) it was displayed as a ligand of the Mn4OxCa cluster. Employing membrane-inlet mass spectrometry (MIMS) and isotope labelling we confirm the release of less than one (approximate to 0.3) HCO3- per PSII upon addition of formate. The same amount of HCO3- release is observed upon formate addition to Mn-depleted PSII samples. This suggests that formate does not replace HCO3- from the donor side, but only from the non-heme iron at the acceptor side of PSII. The absence of a firmly bound HCO3- is corroborated by showing that a reductive destruction of the Mn4OxCa cluster inside the MIMS cell by NH2OH addition does not lead to any CO2/HCO3- release. We note that even after an essentially complete HCO3-/CO2 removal from the sample medium by extensive degassing in the MIMS cell the PSII samples retain 75% of their initial flash-induced O-2-evolving capacity. We therefore conclude that HCO3- has only 'indirect' effects on water-splitting in PSII, possibly by being part of a proton relay network and/or by participating in assembly and stabilization of the water-oxidizing complex. (C) 2008 Elsevier B.V. All rights reserved.
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| 15. |
- Shevela, Dmitriy, et al.
(författare)
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Interactions of photosystem II with bicarbonate, formate and acetate
- 2007
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Ingår i: Photosynthesis Research. - : SPRINGER. - 0166-8595 .- 1573-5079. ; 94:2-3, s. 247-264
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Forskningsöversikt (refereegranskat)abstract
- In this study, we probe the effects of bicarbonate (hydrogencarbonate), BC, removal from photosystem II in spinach thylakoids by measuring flash-induced oxygen evolution patterns (FIOPs) with a Joliot-type electrode. For this we compared three commonly employed methods: (1) washing in BC-free medium, (2) formate addition, and (3) acetate addition. Washing of the samples with buffers depleted of BC and CO2 by bubbling with argon (Method 1) under our conditions leads to an increase in the double hit parameter of the first flash (beta(1)), while the miss parameter and the overall activity remain unchanged. In contrast, addition of 40-50 mM formate or acetate results in a significant increase in the miss parameter and to an similar to 50% (formate) and similar to 10% (acetate) inhibition of the overall oxygen evolution activity, but not to an increased beta(1) parameter. All described effects could be reversed by washing with formate/acetate free buffer and/or addition of 2-10 mM bicarbonate. The redox potential of the water-oxidizing complex (WOC) in samples treated by Method 1 is compared to samples containing 2 mM bicarbonate in two ways: (1) The lifetimes of the S-0, S-2, and S-3 states were measured, and no differences were found between the two sample types. (2) The S-1, S-0, S-1, and S-2 states were probed by incubation with small concentrations of NH2OH. These experiments displayed a subtle, yet highly reproducible difference in the apparent S-i/S-i state distribution which is shown to arise from the interaction of BC with PSII in the already reduced states of the WOC. These data are discussed in detail by also taking into account the CO2 concentrations present in the buffers after argon bubbling and during the measurements. These values were measured by membrane-inlet mass spectrometry (MIMS).
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| 16. |
- Su, Ji-Hu, et al.
(författare)
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Probing mode and site of substrate water binding to the oxygen-evolving complex in the S2 state of photosystem II by 17O-HYSCORE Spectroscopy
- 2008
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 130:3, s. 786-
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Tidskriftsartikel (refereegranskat)abstract
- In the oxygen-evolving complex (OEC) of photosystem II(PSII) molecular oxygen is formed from two substrate water molecules that are ligated to mu-oxo bridged cluster containing four Mn ions and one Ca ion (Mn4OxCa cluster; O-x symbolizes the unknown number of mu-oxo bridges; x >= 5). There is a long-standing enigma as to when, where, and how the two substrate water molecules bind to the Mn4OxCa cluster during the cyclic water-splitting reaction, which involves five distinct redox intermediates (S-i-states; i = 0,...,4). To address this question we employed hyperfine sublevel correlation (HYSCORE) spectroscopy on (H2O)-O-17-enriched PSII samples poised in the paramagnetic S-2 state. This approach allowed us to resolve the magnetic interaction between one solvent exchangeable O-17 that is directly ligated to one or more Mn ions of the Mn4OxCa cluster in the S-2 state of PSII. Direct coordination of O-17 to Mn is supported by the strong (A approximate to 10 MHz) hyperfine coupling. Because these are properties expected from a substrate water molecule, this spectroscopic signature holds the potential for gaining long-sought information about the binding mode and site of one of the two substrate water molecules in the S-2 state of PSII.
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| 17. |
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| 18. |
- Yano, Junko, et al.
(författare)
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High-resolution structure of the photosynthetic Mn4Ca catalyst from X-ray spectroscopy
- 2008
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : ROYAL SOC. - 0962-8436 .- 1471-2970. ; 363:1494, s. 1139-1147
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Tidskriftsartikel (refereegranskat)abstract
- The application of high-resolution X-ray spectroscopy methods to study the photosynthetic water oxidizing complex, which contains a unique hetero-nuclear catalytic Mn4Ca cluster, is described. Issues of X-ray damage, especially at the metal sites in the Mn4Ca cluster, are discussed. The structure of the Mn4Ca catalyst at high resolution, which has so far eluded attempts of determination by X-ray diffraction, X-ray absorption fine structure (EXAFS) and other spectroscopic techniques, has been addressed using polarized EXAFS techniques applied to oriented photosystem II (PSII) membrane preparations and PSII single crystals. A review of how the resolution of traditional EXAFS techniques can be improved, using methods such as range-extended EXAFS, is presented, and the changes that occur in the structure of the cluster as it advances through the catalytic cycle are described. X-ray absorption and emission techniques (XANES and K beta emission) have been used earlier to determine the oxidation states of the Mn4Ca cluster, and in this report we review the use of X-ray resonant Raman spectroscopy to understand the electronic structure of the Mn4Ca cluster as it cycles through the intermediate S-states.
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| 19. |
- Yano, Junko, et al.
(författare)
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Where water is oxidized to dioxygen: : Structure of the photosynthetic Mn4Ca cluster
- 2006
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Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 314:5800, s. 821-825
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of water to dioxygen is catalyzed within photosystem II ( PSII) by a Mn4Ca cluster, the structure of which remains elusive. Polarized extended x-ray absorption fine structure (EXAFS) measurements on PSII single crystals constrain the Mn4Ca cluster geometry to a set of three similar high-resolution structures. Combining polarized EXAFS and x-ray diffraction data, the cluster was placed within PSII, taking into account the overall trend of the electron density of the metal site and the putative ligands. The structure of the cluster from the present study is unlike either the 3.0 or 3.5 angstrom - resolution x-ray structures or other previously proposed models.
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| 20. |
- Yano, J, et al.
(författare)
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X-ray damage to the Mn4Ca complex in single crystals of photosystem II: : A case study for metalloprotein crystallography
- 2005
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - , Phys Biosci Div, Melvin Calvin Lab, Berkeley, CA 94720 USA. Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA. Tech Univ Berlin, Max Volmer Lab Biophys Chem, D-10623 Berlin, Germany. Stanford Synchrotron Radiat Lab, Stanford, CA 94305 USA. European Synchrotron Radiat Facil, F-38043 Grenoble, France. Free Univ Berlin, Inst Kristallog, D-14195 Berlin, Germany. Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany. : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 102:34, s. 12047-12052
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy was used to measure the damage caused by exposure to x-rays to the Mn4Ca active site in single crystals of photosystem II as a function of dose and energy of x-rays, temperature, and time. These studies reveal that the conditions used for structure determination by x-ray crystallography cause serious damage specifically to the metal-site structure. The x-ray absorption spectra show that the structure changes from one that is characteristic of a high-valent Mn-4(III2,IV2), oxo-bridged Mn4Ca cluster to that of Mn(II) in aqueous solution. This damage to the metal site occurs at a dose that is more than one order of magnitude lower than the dose that results in loss of diffractivity and is commonly considered safe for protein crystallography. These results establish quantitative x-ray dose parameters that are applicable to redox-active metalloproteins. This case study shows that a careful evaluation of the structural intactness of the active site(s) by spectroscopic techniques can validate structures derived from crystallography and that it can be a valuable complementary method before structure-function correlations of metalloproteins can be made on the basis of high-resolution x-ray crystal structures.
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| 21. |
- Zein, Samir, et al.
(författare)
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Focusing the view on nature's water-splitting catalyst
- 2008
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : ROYAL SOC. - 0962-8436 .- 1471-2970. ; 363:1494, s. 1167-1177
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Tidskriftsartikel (refereegranskat)abstract
- Nature invented a catalyst about 3 Gyr ago, which splits water with high efficiency into molecular oxygen and hydrogen equivalents (protons and electrons). This reaction is energetically driven by sunlight and the active centre contains relatively cheap and abundant metals: manganese and calcium. This biological system therefore forms the paradigm for all man-made attempts for direct solar fuel production, and several studies are underway to determine the electronic and geometric structures of this catalyst. In this report we briefly summarize the problems and the current status of these efforts and propose a density functional theory-based strategy for obtaining a reliable high-resolution structure of this unique catalyst that includes both the inorganic core and the first ligand sphere.
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