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Tadashi Watanabe - One of the best experts on this subject based on the ideXlab platform.
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species dependence of the redox potential of the Primary Electron donor p700 in photosystem i of oxygenic photosynthetic organisms revealed by spectroelectrochemistry
Plant and Cell Physiology, 2011Co-Authors: Akimasa Nakamura, Tomoyuki Suzawa, Yuki Kato, Tadashi WatanabeAbstract:: The redox potential of the Primary Electron donor P700, E(m)(P700/P700(+)), of Photosystem I (PSI) has been determined for 10 oxygenic photosynthesis organisms, ranging from cyanobacteria, red algae, green algae to higher plants, by spectroelectrochemistry with an optically transparent thin-layer electrode (OTTLE) cell to elucidate the scattering by as much as 150 mV in reported values of E(m)(P700/P700(+)). The E(m)(P700/P700(+)) values determined within error ranges of ± 1-4 mV exhibited a significant species dependence, with a span >70 mV, from +398 to +470 mV vs. the standard hydrogen electrode (SHE). The E(m)(P700/P700(+)) value appears to change systematically in going from cyanobacteria and primitive eukaryotic red algae, then to green algae and higher plants. From an evolutionary point of view, this result suggests that the species believed to appear later in evolution of photosynthetic organisms exhibit higher values of E(m)(P700/P700(+)). Further, the species dependence of E(m)(P700/P700(+)) seems to originate in the species-dependent redox potentials of soluble metalloproteins, Cyt c(6) and plastocyanin, which re-reduce the oxidized P700 in the Electron transfer chain.
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spectroelectrochemical determination of the redox potential of pheophytin a the Primary Electron acceptor in photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Yuki Kato, Miwa Sugiura, Tadashi WatanabeAbstract:Thin-layer cell spectroelectrochemistry, featuring rigorous potential control and rapid redox equilibration within the cell, was used to measure the redox potential Em(Phe a/Phe a−) of pheophytin (Phe) a, the Primary Electron acceptor in an oxygen-evolving photosystem (PS) II core complex from a thermophilic cyanobacterium Thermosynechococcus elongatus. Interferences from dissolved O2 and water reductions were minimized by airtight sealing of the sample cell added with dithionite and mercury plating on the gold minigrid working electrode surface, respectively. The result obtained at a physiological pH of 6.5 was Em(Phe a/Phe a−) = −505 ± 6 mV vs. SHE, which is by ≈100 mV more positive than the values measured ≈30 years ago at nonphysiological pH and widely accepted thereafter in the field of photosynthesis research. Using the P680* − Phe a free energy difference, as estimated from kinetic analyses by previous authors, the present result would locate the Em(P680/P680+) value, which is one of the key parameters but still resists direct measurements, at approximately +1,210 mV. In view of these pieces of information, a renewed diagram is proposed for the energetics in PS II.
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spectroelectrochemical determination of the redox potential of pheophytin a the Primary Electron acceptor in photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Yuki Kato, Miwa Sugiura, Akinori Oda, Tadashi WatanabeAbstract:Thin-layer cell spectroelectrochemistry, featuring rigorous potential control and rapid redox equilibration within the cell, was used to measure the redox potential Em(Phe a/Phe a−) of pheophytin (Phe) a, the Primary Electron acceptor in an oxygen-evolving photosystem (PS) II core complex from a thermophilic cyanobacterium Thermosynechococcus elongatus. Interferences from dissolved O2 and water reductions were minimized by airtight sealing of the sample cell added with dithionite and mercury plating on the gold minigrid working electrode surface, respectively. The result obtained at a physiological pH of 6.5 was Em(Phe a/Phe a−) = −505 ± 6 mV vs. SHE, which is by ≈100 mV more positive than the values measured ≈30 years ago at nonphysiological pH and widely accepted thereafter in the field of photosynthesis research. Using the P680* − Phe a free energy difference, as estimated from kinetic analyses by previous authors, the present result would locate the Em(P680/P680+) value, which is one of the key parameters but still resists direct measurements, at approximately +1,210 mV. In view of these pieces of information, a renewed diagram is proposed for the energetics in PS II.
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spectroelectrochemical determination of the redox potential of p700 in spinach with an optically transparent thin layer electrode
Chemistry Letters, 2004Co-Authors: Akimasa Nakamura, Tomoyuki Suzawa, Tadashi WatanabeAbstract:Optimization of experimental conditions for spectroclectro-chemistry with an optically transparent thin-layer electrode allowed us to determine the redox potential of spinach P700, the Primary Electron donor of photosystem I, to be +469 mV vs. SHE with significantly high reproducibility (′2 mV for 12 independent samples).
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normal phase hplc separation of possible biosynthetic intermediates of pheophytin a and chlorophyll a
Analytical Sciences, 2001Co-Authors: Akimasa Nakamura, Shuhei Tanaka, Tadashi WatanabeAbstract:Normal-phase HPLC conditions have been developed for separating the C173 isoprenoid isomers, which are expected to be formed as biosynthetic intermediates of chlorophyll (Chl) a, Chl a′ (C132-epimer of Chl a), pheophytin (Pheo) a and protochlorophyll (PChl). The application of these conditions to pigment composition analysis of greening etiolated barley leaves allowed us to detect, for the first time, the C173 isomers of Chl a′, a possible constituent of the Primary Electron donor of photosystem (PS) I, P700, and those of Pheo a, the Primary Electron acceptor of PS II, in the very early stage of greening. The C173 isomer distribution patterns were approximately the same between Chl a and Chl a′, but significantly different between Pheo a and Chl a′, probably reflecting the similarity and difference, respectively, in the biosynthetic pathways of these pigment pairs.
Jörg Matysik - One of the best experts on this subject based on the ideXlab platform.
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bacteriopheophytin a in the active branch of the reaction center of rhodobacter sphaeroides is not disturbed by the protein matrix as shown by 13c photo cidnp mas nmr
Journal of Physical Chemistry B, 2013Co-Authors: Karthick Babu Sai Sankar Gupta, Asif Alia, Francesco Buda, Huub J. M. Groot, Jörg MatysikAbstract:The Electronic structure of bacteriopheophytin a (BPhe a), the Primary Electron acceptor (ΦA) in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides, is investigated by photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR spectroscopy at atomic resolution. By using various isotope labeling systems, introduced by adding different 13C selectively labeled δ-aminolevulinic acid precursors in the growing medium of R. sphaeroides wild type (WT), we were able to extract light-induced 13C NMR signals originating from the Primary Electron acceptor. The assignments are backed by theoretical calculations. By comparison of these chemical shifts to those obtained from monomeric BPhe a in solution, it is demonstrated that ΦA in the active branch appears to be Electronically close to free bacteriopheophytin. Hence, there is little effect of the protein surrounding on the cofactor functionally which contributes with its standard redox potentia...
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the Electronic structure of the Primary Electron donor of reaction centers of purple bacteria at atomic resolution as observed by photo cidnp 13c nmr
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Eugenio Daviso, Peter Gast, Shipra Prakash, A Alia, Johannes Neugebauer, Gunnar Jeschke, Jörg MatysikAbstract:Composed of the two bacteriochlorophyll cofactors, PL and PM, the special pair functions as the Primary Electron donor in bacterial reaction centers of purple bacteria of Rhodobacter sphaeroides. Under light absorption, an Electron is transferred to a bacteriopheophytin and a radical pair is produced. The occurrence of the radical pair is linked to the production of enhanced nuclear polarization called photochemically induced dynamic nuclear polarization (photo-CIDNP). This effect can be used to study the Electronic structure of the special pair at atomic resolution by detection of the strongly enhanced nuclear polarization with laser-flash photo-CIDNP magic-angle spinning NMR on the carotenoid-less mutant R26. In the Electronic ground state, PL is strongly disturbed, carrying a slightly negative charge. In the radical cation state, the ratio of total Electron spin densities between PL and PM is 2:1, although it is 2.5:1 for the pyrrole carbons, 2.2:1 for all porphyrinic carbons, and 4:1 for the pyrrole nitrogen. It is shown that the symmetry break between the Electronic structures in the Electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of PL. The significant difference in Electron density distribution between the ground and radical cation states is explained by an electric polarization effect of the nearby histidine.
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Photo-CIDNP solid-state NMR on photosystems I and II:what makes P680 special?
Photosynthesis Research, 2005Co-Authors: Anna Diller, Alia, Peter Gast, Jan Zaanen, Hans J Van Gorkom, Huub J. M. Groot, Clemens Glaubitz, Jörg MatysikAbstract:The origin of the extraordinary high redox potential of P680, the Primary Electron donor of Photosystem II, is still unknown. Photochemically induced dynamic nuclear polarisation (photo-CIDNP) 13C magic-angle spinning (MAS) NMR is a powerful method to study Primary Electron donors. In order to reveal the Electronic structure of P680, we compare new photo-CIDNP MAS NMR data of Photosystem II to those of Photosystem I. The comparison reveals that the Electronic structure of the P680 radical cation is a Chl a cofactor with strong matrix interaction, while the radical cation of P700, the Primary electon donor of Photosystem I, appears to be a Chl a cofactor which is essentially undisturbed. Possible forms of cofactor–matrix interactions are discussed.
Masami Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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identification of the Primary Electron donor in ps ii of the chl d dominated cyanobacterium acaryochloris marina
FEBS Letters, 2004Co-Authors: Mamoru Mimuro, Masami Kobayashi, Machiko Akiyama, Seiji Akimoto, Takanori Gotoh, Makio Yokono, Tohru Tsuchiya, Hideaki Miyashita, Iwao YamazakiAbstract:The Primary Electron donor of photosystem (PS) II in the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina was confirmed by delayed fluorescence (DF) and further proved by pigment contents of cells grown under several light intensities. The DF was found only in the Chl a region, identical to Synechocystis sp. PCC 6803, and disappeared following heat treatment. Pigment analyses indicated that at least two Chl a molecules were present per each two pheophytin a molecules, and these Chl a molecules are assigned to PD1 and PD2. These findings clearly indicate that Chl a is required for water oxidation in PS II.
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the Primary Electron acceptor of green sulfur bacteria bacteriochlorophyll 663 is chlorophyll a esterified with δ 2 6 phytadienol
Photosynthesis Research, 2000Co-Authors: Masami Kobayashi, Tadashi Watanabe, J. Amesz, Hirozo Ohoka, Satoshi Akutsu, Machiko Akiyama, Keisuke Tominaga, Hideo Kise, Fumiko Nishida, Mika KoizumiAbstract:The Primary Electron acceptor of green sulfur bacteria, bacteriochlorophyll (BChl) 663, was isolated at high purity by an improved purification procedure from a crude reaction center complex, and the molecular structure was determined by fast atom bombardment mass spectroscopy (FAB-mass), 1H- and 13C-NMR spectrometry, double quantum filtered correlation spectroscopy (DQF-COSY), heteronuclear multiple-quantum coherence (HMQC) and heteronuclear multiple-bond correlation (HMBC) spectral measurements. BChl 663 was 2.0 mass units smaller than plant Chl a. The NMR spectra showed that the macrocycle was identical to that of Chl a. In the esterifying alcohol, a singlet P71 signal was observed at the high-field side of the singlet P31 signal in BChl 663, while a doublet peak of P71 overlapped that of P111 in Chl a. A signal of P7-proton, seen in Chl a, was lacking, and the P6-proton appeared as a triplet signal near the triplet P2-proton signal in BChl 663. These results indicate the presence in BChl 663 of a C=C double bond between P6 and P7 in addition to that between P2 and P3. The structure of BChl 663 was hence concluded to be Chl a esterified with 2,6-phytadienol instead of phytol. In addition to BChl 663, two molecules of the 132-epimer of BChl a, BChl a′, were found to be present per reaction center, which may constitute the Primary Electron donor.
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study of precise pigment composition of photosystem 1 type reaction centers by means of normal phase hplc
Journal of Plant Research, 1996Co-Authors: Masami KobayashiAbstract:Based on precise pigment analyses of a series of photosystem (PS) 1-type plants, a novel hypothesis is proposed that chiorophyll (Chl)a′ and bacteriochlorophyll (BChl)g′, the 132-epimers of Chla and BChlg, constitute the Primary Electron donors of PS1 and heliobacteria, respectively. Interestingly PS 1-type reaction centers do not have (B) Pheo but have Chl a-like pigments as Primary Electron acceptors.
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The nature of the Primary Electron acceptor in green sulfur bacteria
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1992Co-Authors: Masami Kobayashi, Kazuhito Inoue, Stephan C.m. Otte, C. Erkelens, Peter A. Van Veelen, Tadashi WatanabeAbstract:It was shown previously (Van de Meent, E.J., Kobayashi, M., Erkelens, C., Van Veelen, P.A., Amesz, J. and Watanabe, T. (1991) Biochim. Biophys. Acta 1058, 356–362) by means of HPLC, NMR and optical and mass spectroscopy that the Primary Electron acceptor of heliobacteria is 81-hydroxychlorophyll (Chl) a. In view of the spectral and functional similarities between this pigment and the Primary Electron acceptor of green sulfur bacteria, we have applied the same methods to various species of green sulfur bacteria (Prosthecochloris aestuarii, Chlorobium limicola, C. limicola f. thiosulfatophilum, C. vibrioforme and C. phaeovibrioides) in order to study the identity and the occurrence of the latter pigment. It was already shown from flash spectroscopic and reversed phase HPLC experiments on isolated membranes and solubilized membrane fractions of P. aestuarii that the most likely candidate for the Primary acceptor is a pigment named bacteriochlorophyll (BChl) 663, which had been tentatively identified as a lipophilic from of BChl c. In this communication we will show by means of optical spectroscopy, 252Cf-plasma desorption mass spectroscopy and 1H-NMR that BChl 663 is an isomer of Chl a. This result again emphasizes the similarities between the reaction centers of green sulfur bacteria, heliobacteria and Photosystem I. By means of normal-phase HPLC analysis of the five species of green sulfur bacteria it is shown that BChl 663 is universally present and in comparable quantities in this group of photosynthetic bacteria. No other pigments with similar spectroscopic properties were detected.
Wolfgang Lubitz - One of the best experts on this subject based on the ideXlab platform.
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ultrafast transient absorption studies on photosystem i reaction centers from chlamydomonas reinhardtii 2 mutations near the p700 reaction center chlorophylls provide new insight into the nature of the Primary Electron donor
Biophysical Journal, 2006Co-Authors: Alfred R Holzwarth, Jens Niklas, Marc Muller, Wolfgang LubitzAbstract:The energy transfer and charge separation kinetics in several core Photosystem I particles of Chlamydomonas reinhardtii with point mutations around the PA and PB reaction center chlorophylls (Chls) have been studied using ultrafast transient absorption spectroscopy in the femtosecond to nanosecond time range to characterize the influence on the early Electron transfer processes. The data have been analyzed in terms of kinetic compartment models. The adequate description of the transient absorption kinetics requires three different radical pairs in the time range up to ∼100 ps. Also a charge recombination process from the first radical pair back to the excited state is present in all the mutants, as already shown previously for the wild-type (Muller, M. G., J. Niklas, W. Lubitz, and A. R. Holzwarth. 2003. Biophys. J. 85:3899–3922; and Holzwarth, A. R., M. G. Muller, J. Niklas, and W. Lubitz. 2005. J. Phys. Chem. B. 109:5903–59115). In all mutants, the Primary charge separation occurs with the same effective rate constant within the error limits as in the wild-type (»350 ns−1), which implies an intrinsic rate constant of charge separation of <1 ps−1. The rate constant of the secondary Electron transfer process is slowed down by a factor of ∼2 in the mutant B-H656C, which lacks the ligand to the central metal of Chl PB. For the mutant A-T739V, which breaks the hydrogen bond to the keto carbonyl of Chl PA, only a slight slowing down of the secondary Electron transfer is observed. Finally for mutant A-W679A, which has the Trp near the PA Chl replaced, either no pronounced effect or, at best, a slight increase on the secondary Electron transfer rate constants is observed. The effective charge recombination rate constant is modified in all mutants to some extent, with the strongest effect observed in mutant B-H656C. Our data strongly suggest that the Chls of the PA and PB pair, constituting what is traditionally called the “Primary Electron donor P700”, are not oxidized in the first Electron transfer process, but rather only in the secondary Electron transfer step. We thus propose a new Electron transfer mechanism for Photosystem I where the accessory Chl(s) function as the Primary Electron donor(s) and the A0 Chl(s) are the Primary Electron acceptor(s). This new mechanism also resolves in a straightforward manner the difficulty with the previous mechanism, where an Electron would have to overcome a distance of ∼14 A in <1 ps in a single step. If interpreted within a scheme of single-sided Electron transfer, our data suggest that the B-branch is the active branch, although parallel A-branch activity cannot be excluded. All the mutations do affect to a varying extent the energy difference between the reaction center excited state RC* and the first radical pair and thus affect the rate constant of charge recombination. It is interesting to note that the new mechanism proposed is in fact analogous to the Electron transfer mechanism in Photosystem II, where the accessory Chl also plays the role of the Primary Electron donor, rather than the special Chl pair P680 (Prokhorenko, V. and A. R. Holzwarth. 2000. J. Phys. Chem. B. 104:11563–11578).
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molecular orbital study of the Primary Electron donor p700 of photosystem i based on a recent x ray single crystal structure analysis
Principles and Practice of Constraint Programming, 2003Co-Authors: M Plato, Norbert Kraus, Petra Fromme, Wolfgang LubitzAbstract:Abstract The X-ray structure analysis of photosystem (PS) I single crystals showed that the Primary Electron donor P700 is a heterodimer formed by one chlorophyll (Chl) a and one Chl a ′ [Nature 411 (2001) 909]. The Electronic structure of the cation radical P700 + of the Primary donor, which is created in the charge separation process, has been probed by semiempirical molecular orbital calculations including spin polarization effects (RHF-INDO/SP). The calculations, which were based on the X-ray structure, clearly show that P700 is a supermolecule formed by two chlorophyll species. They furthermore predict an asymmetrical charge and spin density distribution in favor of the monomeric Chl a half of this dimer in accordance with results from earlier EPR and ENDOR studies [J. Phys. Chem. B 105 (2000) 1225]. The stepwise inclusion of various electrostatic interactions of the dimer with its nearest surrounding (one threonine forming a hydrogen bond to the keto group of Chl a ′ and two histidines liganding the Mg atoms of the two chlorophylls) leads to a systematic enhancement of this Electronic asymmetry yielding a spin density ratio of almost 5:1 as also found experimentally. A large part of this value is caused by spin polarization effects. This result is only weakly affected by the electrostatic field of more remote amino acid residues and other pigment molecules (‘accessory’ Chl a molecules) present in PS I. A separate group of calculations involving local geometry optimizations by energy minimization techniques yields a further enhancement of the spin density asymmetry. A particularly strong effect is obtained by allowing for variations of the geometry of the vinyl groups on both chlorophylls of the P700 dimer. Theoretical results for individual isotropic proton and nitrogen hyperfine coupling constants, showing a satisfactory agreement with experimental findings, are also presented.
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p700 the Primary Electron donor of photosystem i
Biochimica et Biophysica Acta, 2001Co-Authors: Andrew N Webber, Wolfgang LubitzAbstract:Abstract The Primary Electron donor of photosystem I, P700, is a chlorophyll species that in its excited state has a potential of approximately −1.2 V. The precise chemical composition and Electronic structure of P700 is still unknown. Recent evidence indicates that P700 is a dimer of one chlorophyll (Chl) a and one Chl a ′. The Chl a ′ and Chl a are axially coordinated by His residues provided by protein subunits PsaA and PsaB, respectively. The Chl a ′, but not the Chl a , is also H-bonded to the protein. The H-bonding is likely responsible for selective insertion of Chl a ′ into the reaction center. EPR studies of P700 +⋅ in frozen solution and single crystals indicate a large asymmetry in the Electron spin and charge distribution towards one Chl of the dimer. Molecular orbital calculations indicate that H-bonding will specifically stabilize the Chl a ′-side of the dimer, suggesting that the unpaired Electron would predominantly reside on the Chl a . This is supported by results of specific mutagenesis of the PsaA and PsaB axial His residues, which show that only mutations of the PsaB subunit significantly alter the hyperfine coupling constants associated with a single Chl molecule. The PsaB mutants also alter the microwave induced triplet-minus-singlet spectrum indicating that the triplet state is localized on the same Chl. Excitonic coupling between the two Chl a of P700 is weak due to the distance and overlap of the porphyrin planes. Evidence of excitonic coupling is found in PsaB mutants which show a new bleaching band at 665 nm that likely represents an increased intensity of the upper exciton band of P700. Additional properties of P700 that may give rise to its unusually low potential are discussed.
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site directed mutagenesis of thr a739 of photosystem i in chlamydomonas reinhardtii alters significantly the excitonic and Electronic coupling of the Primary Electron donor p700
Science Access, 2001Co-Authors: Witt Heike, Enrica Bordignon, Eberhard Schlodder, Christian Teutloff, Donatella Carbonera, Jens Niklas, Wolfgang LubitzAbstract:The Primary Electron donor P700 of photosystem I is a dimer comprised of one chlorophyll (Chl) a (PB) and one Chl a´ (PA). To investigate the influence of protein-cofactor interactions on the properties of P700, we constructed a series of site-directed mutants in the surrounding of P700. The most interesting effects were obtained for the replacement of Thr A739, a possible hydrogen bond donor to the 9-keto group of PA, against Val. The low-energy exciton absorption band of P700 observed as a shoulder at about 700 nm in the absorption spectrum of PS I complexes from wild type is not visible in the mutant TV A739. The main bleaching band in the (P700+-P700) and (3P700-P700) absorption difference spectra is blue shifted by 9 nm. Both results imply that the excitonic coupling of P700 is severely disturbed. A similar blue shift is observed for the main bleaching in the Soret region. Redox titrations yielded a decrease of the midpoint potential for the oxidation of P700 by 32 mV. ENDOR spectroscopy revealed a change of the Electron spin densitiy distribution of P700+. The data provide evidence that P700 is a Chl-dimer with an asymmetric spin/charge density distribution.
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relationship between the oxidation potential and Electron spin density of the Primary Electron donor in reaction centers from rhodobacter sphaeroides
Proceedings of the National Academy of Sciences of the United States of America, 1997Co-Authors: Katie Artz, Joann Williams, Jim Allen, Friedhelm Lendzian, J Rautter, Wolfgang LubitzAbstract:The Primary Electron donor in bacterial reaction centers is a dimer of bacteriochlorophyll a molecules, labeled L or M based on their proximity to the symmetry-related protein subunits. The Electronic structure of the bacteriochlorophyll dimer was probed by introducing small systematic variations in the bacteriochlorophyll–protein interactions by a series of site-directed mutations that replaced residue Leu M160 with histidine, tyrosine, glutamic acid, glutamine, aspartic acid, asparagine, lysine, and serine. The midpoint potentials for oxidation of the dimer in the mutants showed an almost continuous increase up to ≈60 mV compared with wild type. The spin density distribution of the unpaired Electron in the cation radical state of the dimer was determined by Electron–nuclear–nuclear triple resonance spectroscopy in solution. The ratio of the spin density on the L side of the dimer to the M side varied from ≈2:1 to ≈5:1 in the mutants compared with ≈2:1 for wild type. The correlation between the midpoint potential and spin density distribution was described using a simple molecular orbital model, in which the major effect of the mutations is assumed to be a change in the energy of the M half of the dimer, providing estimates for the coupling and energy levels of the orbitals in the dimer. These results demonstrate that the midpoint potential can be fine-tuned by electrostatic interactions with amino acids near the dimer and show that the properties of the Electronic structure of a donor or acceptor in a protein complex can be directly related to functional properties such as the oxidation–reduction midpoint potential.
Qiang Yuan - One of the best experts on this subject based on the ideXlab platform.
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explanation of nearby snrs for Primary Electron excess and proton spectral bump
arXiv: High Energy Astrophysical Phenomena, 2021Co-Authors: Tianpeng Tang, Ziqing Xia, Zhaoqiang Shen, Lei Feng, Qiang Yuan, Yizhong FanAbstract:Several groups have reported a possible excess of Primary Electrons at high energies with the joint fit of the positron fraction and total Electron/positron spectra. With the latest release of high-precision Electron/positron spectra measured by AMS-02, we further confirm this excess by fitting $\Delta\Phi$$\rm(i.e., \Phi_{e^-}-\Phi_{e^+})$ data in this work. Then we investigate the contribution of a single nearby supernova remnant to the Primary Electron excess and find that Monogem can reasonably account for this excess. Moreover, we predict that the Electron spectrum may harden again at a few TeVs due to Vela's contribution. DAMPE, which can accurately measure Electrons at TeV scale, is expected to provide the robust test of this new spectral feature in the near future. Finally, we fit the proton spectrum data of DAMPE with Monogem or Loop I. We find that both the Primary Electron excess and the proton spectral bump could be mainly generated by Monogem.
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quantitative study of the ams 02 Electron positron spectra implications for pulsars and dark matter properties
Physical Review D, 2015Co-Authors: Sujie Lin, Qiang YuanAbstract:The Alpha Magnetic Spectrometer (AMS-02) has just published the unprecedentedly precise measurement of the cosmic Electron and positron spectra. In this paper, we try to give a quantitative study on the AMS-02 results by a global fitting to the Electron and positron spectra, together with the updated positron fraction data. The Markov chain Monte Carlo algorithm is adopted to do the fitting. The Primary Electron spectrum and the parameters for pulsars or dark matter that contribute extra positrons are determined simultaneously. We find that there is a hardening of the Primary Electron spectrum at similar to 60 GeV. With such a new feature at the background spectrum, both the pulsars and dark matter can explain the AMS-02 results very well. The dark matter scenario shows a drop at the positron fraction at similar to 300 GeV but suffers very strong constraints from Fermi gamma-ray observations. The fitting results also suggest that the propagation model with convection may be more favored by the lepton data than the reacceleration model.
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reconcile the ams 02 positron fraction and fermi lat hess total e spectra by the Primary Electron spectrum hardening
Physics Letters B, 2013Co-Authors: Qiang YuanAbstract:The recently reported positron fraction up to similar to 350 GeV by AMS-02 seems to have tension with the total Electron/positron spectra detected by Fermi and HESS, for either pulsar or dark matter annihilation/decay scenario as the Primary positron sources. In this work we will show that the tension will be removed by an adjustment of the Primary Electron spectrum. If the Primary Electron spectrum becomes harder above similar to 50 GeV, similar as the cosmic ray nuclei spectrum, the AMS-02 positron fraction and Fermi/HESS data can be well fitted by both the pulsar and dark matter models. This result may be suggestive of a common origin of the cosmic ray nuclei and the Primary Electrons. Furthermore, this study also implies that the properties of the extra sources derived from the fitting to the AMS-02 data should depend on the form of background. (C) 2013 Elsevier B.V. All rights reserved.
