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G Renger - One of the best experts on this subject based on the ideXlab platform.

  • reaction coordinate of P680 o reduction by yz in ps ii core complexes from spinach
    Science Access, 2001
    Co-Authors: Philipp Kühn, H.-j. Eckert, Ronald Steffen, Nicola Iwanowski, Klaus-dieter Irrgang, H J Eichler, G Renger
    Abstract:

    Photosynthetic water oxidation to molecular oxygen and four protons is energetically driven by the cation radical P680+ that is formed as a result of light induced primary charge separation. Electron transfer from the redox active tyrosine residue YZ of polypeptide D1 leads to rapid reduction of P680+ via surprisingly complex multiphasic kinetics which comprise two components ("fast" and "slow") in the ns time domain. The present study reveals that in untreated isolated PSII core complexes from spinach the normalized extent of ns kinetics is significantly enhanced by addition of Ca2+. This effect is specific for Ca2+ and most pronounced at moderately acidic pH. Although Ca2+ also leads to an increase of the average oxygen yield per flash, a strict correlation does not exist between this parameter and the kinetic pattern of P680 reduction. The activation energy of electron transfer from YZ to P680+ in the ns time domain is of the order of 10 kJ/mol and virtually independent of Ca2+. It is concluded that the electron transfer via the "fast" ns kinetics is not limited by trigger reactions and thus follows the Marcus-relation for a nonadiabatic redox step. The slower reactions leading to further P680+ reduction are assumed to be triggered by "short" and "long" range relaxation processes that take place in the protein matrix with different underlying mechanisms and time constants.

  • P680 reduction kinetics and redox transition probability of the water oxidizing complex as a function of ph and h d isotope exchange in spinach thylakoids
    Biochemistry, 1999
    Co-Authors: G Christen, And A Seeliger, G Renger
    Abstract:

    : The rise of fluorescence as an indicator for P680(+)* reduction by YZ and the period-four oscillation of oxygen yield induced by a train of saturating flashes were measured in dark-adapted thylakoids as a function of pH in the absence of exogenous electron acceptors. The results reveal that: (i) the average amplitude of the nanosecond kinetics and the average of the maximum fluorescence attained at 100 micros after the flash in the acidic range decrease with decreasing pH; (ii) the oxygen yield exhibits a pronounced period-four oscillation at pH 6.5 and higher damping at both pH 5.0 and pH 8.0; (iii) the probability of misses in the Si-state transitions of the water oxidizing complex is affected characteristically when exchangeable protons are replaced by deuterons [at pH 7.0 values of <1 are observed]. The results are discussed within the framework of a combined mechanism for P680(+)* reduction where the nanosecond kinetics reflect an electron transfer coupled with a "rocket-type" proton shift within a hydrogen bridge from YZ to a nearby basic group, X [Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431], and subsequent relaxations within a network of hydrogen bonds. It is concluded that in the acidic region the hydrogen bond between YZ and X (most likely His 190 of polypeptide D1) is interrupted either by direct protonation of X or by conformational changes due to acid-induced Ca2+ release. This gives rise to a decreased P680(+)* reduction by nanosecond kinetics and an increase of dissipative P680(+)* recombination at low pH. A different mechanism is responsible for the almost invariant amplitude of nanosecond kinetics and increase of alpha in the alkaline region.

  • the role of hydrogen bonds for the multiphasic P680 reduction by yz in photosystem ii with intact oxyen evolution capacity analysis of kinetic h d isotope exchange effects
    Biochemistry, 1999
    Co-Authors: G Christen, G Renger
    Abstract:

    The mechanism of multiphasic P680(+)* reduction by YZ has been analyzed by studying H/D isotope exchange effects on flash-induced changes of 830 nm absorption, DeltaA830(t), and normalized fluorescence yield, F(t)/F0, in dark-adapted thylakoids and PS II membrane fragments from spinach. It was found that (a) the characteristic period four oscillations of the normalized components of DeltaA830(t) relaxation and of F(t)/F0 rise in the nanosecond and microsecond time domain are significantly modified when exchangeable protons are replaced by deuterons; (b) in marked contrast to the normalized steady-state extent of the microsecond kinetics of 830 nm absorption changes which increases only slightly due to H/D exchange (about 10%) the Si state-dependent pattern exhibits marked effects that are most pronounced after the first, fourth, fifth, and eighth flashes; (c) regardless of data evaluation by different fit procedures the results lead to a consistent conclusion, that is, the relative extent of the back reaction between P680(+)*QA-* becomes enhanced in samples suspended in D2O; and (d) this enhancement is dependent on the Si state of the WOC and attains maximum values in S2 and S3, most likely due to a retardation of the "35 micros kinetics" of P680(+)* reduction. In an extension of our previous suggestion on the functional role of hydrogen bonding of YZ by a basic group X (Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431), a model is proposed for the origin of the multiphasic P680(+)* reduction by YZ. Two types of different processes are involved: (a) electron transfer in the nanosecond time domain is determined by strength and geometry of the hydrogen bond between the O-H group of YZ and acceptor X, and (b) the microsecond kinetics reflect relaxation processes of a hydrogen bond network giving rise to a shift of the equilibrium P680(+)*YZ P680YZ(OX) toward the right side. The implications of this model are discussed.

  • on the origin of the 35 μs kinetics of P680 reduction in photosystem ii with an intact water oxidising complex
    FEBS Letters, 1998
    Co-Authors: G Christen, F. Reifarth, G Renger
    Abstract:

    The origin of the `35-μs kinetics' of P680+⋅ reduction in photosystem II (PS II) with an intact water oxidising complex has been analysed by comparative measurements of laser flash induced changes of the 830-nm absorption and the relative quantum yield of chlorophyll (Chl) fluorescence. The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F., Christen, G. and Renger, G. (1997) Photosynth. Res. 51, 231–242]. It was found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted samples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35-μs kinetics under identical excitation conditions are strikingly different with maxima after the 3rd and 5th flash for the 830-nm absorption changes vs. pronounced maxima after the 4th and 8th flash for the rise of the fluorescence yield. The period four oscillations unambiguously show that the `35-μs kinetics' of P680+⋅ reduction are characteristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) indicates that in contrast to the ns components of P680+⋅ reduction the 35-μs kinetics do not reflect exclusively an electron transfer from YZ to P680+⋅. It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680+⋅ reduction by YZ and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield.

  • pulsed epr measurement of the distance between P680 and qa in photosystem ii
    FEBS Letters, 1997
    Co-Authors: Stephan G. Zech, H.-j. Eckert, G Renger, Wolfgang Lubitz, Jens Kurreck, Robert Bittl
    Abstract:

    Out-of-phase electron spin echo envelope modulation (ESEEM) spectroscopy was used to determine the distance between the primary donor radical cation P680+. and the quinone acceptor radical anion Q(A)-. in iron-depleted photosystem II in membrane fragments from spinach that are deprived of the water oxidizing complex. Furthermore, a lower limit for the distance between the oxidized tyrosine residue Y(Z) of polypeptide D1 and Q(A)-. could be estimated by a comparison of data gathered from samples where the electron transfer from Y(Z) to P680+. is either intact or blocked by preillumination in the presence of NH2OH.

Gernot Renger - One of the best experts on this subject based on the ideXlab platform.

  • Chapter 16:Functional Pattern of Photosystem II
    Comprehensive Series in Photochemical & Photobiological Sciences, 2007
    Co-Authors: Gernot Renger
    Abstract:

    This chapter reviews our current knowledge on the energetics, kinetics, and mechanism of electron transfer in Photosystem II (PS II), excluding oxidative water splitting, which is outlined in Chapter 17. Similarities of PS II with the reaction centers of anoxygenic (non-oxygen evolving) purple bacteria in the general functional and structural organization of charge separation and quinol formation are outlined. The striking differences are discussed that emerge from the thermodynamic requirements for water oxidation to molecular oxygen and four protons, i.e., the generation of electron holes of sufficiently strong oxidizing power. An understanding of the nature and the properties of the photoactive component P680 as the site of photochemical hole formation is of central relevance. The unique properties of P680 are best described by assigning P680 to a special multichromophoric unit (Chl a)4 Pheox with x = 0, 1 or 2 (the value of x is a matter of controversy), rather than a single chromophore or special pair. The possible electronic structures of 1P680*, 3P680 and P680+˙ are discussed. It is emphasized that the surrounding protein matrix forms an integral and decisive part of the functional properties of P680, in particular for its extraordinarily high reduction potential. Evidence is presented that in the first electron transfer event of charge separation a “monomeric” type Chl a within P680 transfers an electron from its excited singlet state to an associated pheophytin (Pheo)a molecule, which acts as the primary electron acceptor. This event is followed by rapid spin redistribution, leading to predominant localization of the electron hole on a Chl a in P680+˙ designated as PD1, which is part of a “dimeric” structural motif termed PD1PD2 and is in close proximity to the redox-active tyrosine YZ. The subsequent reactions of P680+˙reduction by YZ and of PQH2 formation via a two-step, one-electron reaction sequence with Q−˙A as reductant are described with special emphasis on the role of the protein dynamics for energetics and kinetics.

  • Analysis of the P680+. reduction pattern and its temperature dependence in oxygen-evolving PS II core complexes from thermophilic cyanobacteria and higher plants
    Physical Chemistry Chemical Physics, 2004
    Co-Authors: P. Kühn, Hans Joachim Eichler, H.-j. Eckert, Gernot Renger
    Abstract:

    The multiphasic P680+. reduction kinetics by YZ and their temperature dependence were investigated in PS II core complexes with high oxygen evolution capacity, isolated from a thermophilic cyanobacterium (Thermosynechococcus elongatus) and a higher plant (Spinacea oleracea). Measurements and kinetic analyses of laser flash induced 820 nm absorption changes (reflecting the turnover of P680) led to the following results: (a) the pattern of multiphasic P680+. reduction is basically the same in both species, (b) the activation energy of the "fast" nanosecond kinetics is 20 ? 5 kJ mol-1 and 14 ? 5 kJ mol-1 for the samples from T. elongatus and S. oleracea, respectively, (c) the activation energies of this reaction are nearly the same in complexes with water oxidizing complex (WOC) in redox states S1 and S2, (d) the activation energy of the "slow" nanosecond kinetics ascribed to "local" relaxation processes is larger by almost a factor of two compared to that of the "fast" nanosecond kinetics, and (e) the normalized amplitudes of the "fast" and "slow" nanosecond kinetics are virtually independent of temperature in the physiological range for PS II core complexes from both organisms. Based on these findings the energetics and kinetics of P680+. reduction in fully competent PS II is briefly discussed within the framework of a dynamic model of sequential relaxation processes. The protein dynamics are inferred to provide the major contribution to the driving force of the redox reaction.

  • Time-resolved monitoring of flash induced changes of fluorescence quantum yield in spinach thylakoids
    Science Access, 2001
    Co-Authors: Ronald Steffen, Gernot Renger
    Abstract:

    The anionic and cationic chlorin radicals P680+ and Pheo- of photosystem II (PSII) act as powerful nonphotochemical quenchers of chlorophyll fluorescence. After excitation with short laser flashes the primary radical pair P680+Pheo- is formed and stabilized by rapid electron transfer from Pheo- to QA via a 300 ps kinetics. Accordingly, PSII reaction centers populate the state P680+QA- about 1 ns after a saturating short laser pulse. The subsequent reduction of P680+ by the redox active tyrosine Y within the ns-timescale removes the quencher P680+ and the fluorescence quantum yield rises until the photochemical quencher QA becomes restored by Q A- reoxidation via markedly slower m s-kinetics with QB (Q B-). This offers the possibility to measure the kinetics of P680+ reduction with Yz monitoring flash induced changes of fluorescence quantum yield with sufficiently high time resolution. The present study describes new equipment that satisfies this condition by using a rapidly gated multichannel plate detector in order to eliminate distortions due to fluorescence induced by the strong actinic flash. This method is especially suited for noninvasive analyses of the reaction pattern of P680+ reduction of PSII with intact water oxidation in thylakoids and whole algal cells. Data analyses require a suitable separation of signals that originate from the transient formation of carotenoid triplets. The applicability of the new assay is illustrated.

  • Reaction coordinate of P680+o reduction by YZ in PS II core complexes from spinach
    Science Access, 2001
    Co-Authors: Philipp Kühn, H.-j. Eckert, Ronald Steffen, Nicola Iwanowski, Klaus-dieter Irrgang, Hans Joachim Eichler, Gernot Renger
    Abstract:

    Photosynthetic water oxidation to molecular oxygen and four protons is energetically driven by the cation radical P680+ that is formed as a result of light induced primary charge separation. Electron transfer from the redox active tyrosine residue YZ of polypeptide D1 leads to rapid reduction of P680+ via surprisingly complex multiphasic kinetics which comprise two components ("fast" and "slow") in the ns time domain. The present study reveals that in untreated isolated PSII core complexes from spinach the normalized extent of ns kinetics is significantly enhanced by addition of Ca2+. This effect is specific for Ca2+ and most pronounced at moderately acidic pH. Although Ca2+ also leads to an increase of the average oxygen yield per flash, a strict correlation does not exist between this parameter and the kinetic pattern of P680 reduction. The activation energy of electron transfer from YZ to P680+ in the ns time domain is of the order of 10 kJ/mol and virtually independent of Ca2+. It is concluded that the electron transfer via the "fast" ns kinetics is not limited by trigger reactions and thus follows the Marcus-relation for a nonadiabatic redox step. The slower reactions leading to further P680+ reduction are assumed to be triggered by "short" and "long" range relaxation processes that take place in the protein matrix with different underlying mechanisms and time constants.

  • On the origin of the `35-μs kinetics' of P680+⋅ reduction in photosystem II with an intact water oxidising complex
    FEBS letters, 1998
    Co-Authors: G Christen, F. Reifarth, Gernot Renger
    Abstract:

    The origin of the `35-μs kinetics' of P680+⋅ reduction in photosystem II (PS II) with an intact water oxidising complex has been analysed by comparative measurements of laser flash induced changes of the 830-nm absorption and the relative quantum yield of chlorophyll (Chl) fluorescence. The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F., Christen, G. and Renger, G. (1997) Photosynth. Res. 51, 231–242]. It was found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted samples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35-μs kinetics under identical excitation conditions are strikingly different with maxima after the 3rd and 5th flash for the 830-nm absorption changes vs. pronounced maxima after the 4th and 8th flash for the rise of the fluorescence yield. The period four oscillations unambiguously show that the `35-μs kinetics' of P680+⋅ reduction are characteristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) indicates that in contrast to the ns components of P680+⋅ reduction the 35-μs kinetics do not reflect exclusively an electron transfer from YZ to P680+⋅. It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680+⋅ reduction by YZ and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield.

Eberhard Schlodder - One of the best experts on this subject based on the ideXlab platform.

  • Temperature dependence of the oxidation kinetics of TyrZ and TyrD in oxygen-evolving photosystem II complexes throughout the range from 320K to 5K.
    Biochimica et biophysica acta, 2015
    Co-Authors: Eberhard Schlodder, Marianne Çetin, Friedhelm Lendzian
    Abstract:

    Abstract The photo-induced oxidation of Tyr Z and Tyr D by P680 •+ , that involves both electron and proton transfer (PCET), has been studied in oxygen-evolving photosystem II from Thermosynechococcus elongatus . We used time-resolved absorption spectroscopy to measure the kinetics of P680 •+ reduction by tyrosine after the first flash given to dark-adapted PS II as a function of temperature and pH. The half-life of Tyr Z oxidation by P680 •+ increases from 20 ns at 300 K to about 4 μs at 150 K. Analyzing the temperature dependence of the rate, one obtains a reorganization energy of about 770 meV. Between 260 K and 150 K, the reduction of P680 •+ by Tyr Z is increasingly replaced by charge recombination between P680 •+ and Q A •− . We propose that the driving force for Tyr Z oxidation by P680 •+ decreases upon lowering the temperature. Tyr Z oxidation cannot be excluded in a minority of PS II complexes at cryogenic temperatures. Tyr D oxidation by P680 •+ with a half-life of about 30 ns was observed at high pH. The pH dependence of the yield of Tyr D oxidation can be described by a single protonable group with a pK of approximately 8.4. The rate of Tyr D oxidation by P680 •+ is virtually identical upon substitution of solvent exchangeable protons with deuterons indicating that the rate is limited by electron transfer. The rate is independent of temperature between 5 K and 250 K. It is concluded that Tyr D donates the electron to P680 •+ via P D2 .

  • Temperature Dependence of the Reduction Kinetics of P680002B; in Oxygen-Evolving PS II Complexes Throughout the Range from 320 to 80 K
    Photosynthesis. Energy from the Sun, 2008
    Co-Authors: Eberhard Schlodder
    Abstract:

    Transient absorbance difference spectroscopy has been used to study the reduction kinetics of P680+ after the first flash given to darkadapted oxygen-evolving PS II complexes from Thermosynechococcus elongatus as a function of temperature between 80 and 320 K. The half-life of P680+ reduction by TyrZ increases from 20 ns at 300 K to about 4 μs at 150 K corresponding to an activation energy of (122 ± 3) meV. Analyzing the temperature dependence of the rate in terms of nonadiabatic electron transfer theory, one obtains a reorganization energy of about 700 meV and an edge-to-edge distance of about 8.5 A which is in good agreement with the distance between PD1 and TyrZ in the recent structural model of PS II at 3.0 A resolution (Loll et al. 2005). In the range from 260 to 150 K, the re-reduction of P680+ by TyrZ is increasingly replaced by the charge recombination between P680+ and QA −. It is proposed that reorganization processes which are required for the stabilization of the state P680TyrZ ox become arrested around 200 K. Freezing out of the electron donation from TyrZ to P680+ is the result. The yield of TyrZ oxidation at low temperature is

  • 3 P680 in Photosystem II with Singly Reduced Q A
    Photosynthesis: Mechanisms and Effects, 1998
    Co-Authors: Eberhard Schlodder, Klaus Brettel, B Hillmann, F. Mallwitz
    Abstract:

    Photosystem II (PS II) is a membrane-bound pigment-protein complex that uses light energy to drive the transfer of electrons from water to plastoquinone. When the electron transfer to the quinone acceptors is blocked, the primary radical pair, P680+Pheo-, can decay by three pathways: (i) by charge recombination to the singlet ground state, (ii) by an activated back reaction to the excited singlet state of P680 and (iii) after singlet-triplet mixing in the radical pair by recombination to the lowest excited triplet state of P680, 3P680. In PS II centers, in which the first quinone acceptor, QA, is removed or doubly reduced (QAH2), the formation of 3P680 can be monitored by the characteristic spin-polarized triplet EPR spectrum. The lifetime of 3P680 is similar to that of the chlorophyll a triplet state in solvents (τ ≈ 1.4 ms (70%)/7 ms (30%) at 5 K and τ ≈ 1.4 ms at T > 20 K under anaerobic conditions). In the presence of singly reduced QA, however, the P680 triplet state with ms lifetime could not be detected, neither by transient absorption spectroscopy nor by cw-EPR [1]. In more recent work, transient absorption spectroscopy at low temperature (T = 25 K) revealed that the primary radical pair decays to an intermediate with μs lifetime (τ ≈ 2 μs (50%)/20 μs (50%) at 25 K). From its spectral features in the QY-region, this intermediate has been identified with the triplet state of P680 [2,3].

  • Endor and Transient Absorption Studies of P680 +· and Other Cation Radicals in PSII Reaction Centres Before and After Inactivation of Secondary Electron Donors
    Photosynthesis: Mechanisms and Effects, 1998
    Co-Authors: Alison Telfer, Eberhard Schlodder, Friedhelm Lendzian, James Barber, Wolfgang Lubitz
    Abstract:

    The aim of this study was to explore the electronic structure of the radical cation of the primary electron donor in the PSII reaction centre, P680, using ENDOR spectroscopy. This technique has been used to elucidate the electronic structure of the oxidised primary donors in purple bacteria (1) and P700 (2,3). However, there has only been one report of similar ENDOR studies on P680+· (2). Study of P680+· is hampered by the fact that its very high redox potential results in oxidation of secondary electron donors (4–6). Here we have compared untreated PSII RC with samples in which secondary donors were inactivated.

  • endor and transient absorption studies of P680 and other cation radicals in psii reaction centres before and after inactivation of secondary electron donors
    1998
    Co-Authors: Eberhard Schlodder, Friedhelm Lendzian, James Barber, Alison Telfer, Wolfgang Lubitz
    Abstract:

    The aim of this study was to explore the electronic structure of the radical cation of the primary electron donor in the PSII reaction centre, P680, using ENDOR spectroscopy. This technique has been used to elucidate the electronic structure of the oxidised primary donors in purple bacteria (1) and P700 (2,3). However, there has only been one report of similar ENDOR studies on P680+· (2). Study of P680+· is hampered by the fact that its very high redox potential results in oxidation of secondary electron donors (4–6). Here we have compared untreated PSII RC with samples in which secondary donors were inactivated.

T. Noguchi - One of the best experts on this subject based on the ideXlab platform.

  • genetically introduced hydrogen bond interactions reveal an asymmetric charge distribution on the radical cation of the special pair chlorophyll P680
    Journal of Biological Chemistry, 2017
    Co-Authors: Ryo Nagao, Motoki Yamaguchi, Shin Nakamura, Hanayo Ueokanakanishi, T. Noguchi
    Abstract:

    The special-pair chlorophyll (Chl) P680 in photosystem II has an extremely high redox potential (Em ) to enable water oxidation in photosynthesis. Significant positive-charge localization on one of the Chl constituents, PD1 or PD2, in P680+ has been proposed to contribute to this high Em To identify the Chl molecule on which the charge is mainly localized, we genetically introduced a hydrogen bond to the 131-keto C=O group of PD1 and PD2 by changing the nearby D1-Val-157 and D2-Val-156 residues to His, respectively. Successful hydrogen bond formation at PD1 and PD2 in the obtained D1-V157H and D2-V156H mutants, respectively, was monitored by detecting 131-keto C=O vibrations in Fourier transfer infrared (FTIR) difference spectra upon oxidation of P680 and the symmetrically located redox-active tyrosines YZ and YD, and they were simulated by quantum-chemical calculations. Analysis of the P680+/P680 FTIR difference spectra of D1-V157H and D2-V156H showed that upon P680+ formation, the 131-keto C=O frequency upshifts by a much larger extent in PD1 (23 cm-1) than in PD2 ( .

  • Genetically introduced hydrogen bond interactions reveal an asymmetric charge distribution on the radical cation of the special-pair chlorophyll P680.
    The Journal of biological chemistry, 2017
    Co-Authors: Ryo Nagao, Motoki Yamaguchi, Shin Nakamura, Hanayo Ueoka-nakanishi, T. Noguchi
    Abstract:

    The special-pair chlorophyll (Chl) P680 in photosystem II has an extremely high redox potential (Em) to enable water oxidation in photosynthesis. Significant positive-charge localization on one of the Chl constituents, PD1 or PD2, in P680+ has been proposed to contribute to this high Em. To identify the Chl molecule on which the charge is mainly localized, we genetically introduced a hydrogen bond to the 131-keto C=O group of PD1 and PD2 by changing the nearby D1-Val-157 and D2-Val-156 residues to His, respectively. Successful hydrogen bond formation at PD1 and PD2 in the obtained D1-V157H and D2-V156H mutants, respectively, was monitored by detecting 131-keto C=O vibrations in Fourier transfer infrared (FTIR) difference spectra upon oxidation of P680 and the symmetrically located redox-active tyrosines YZ and YD, and they were simulated by quantum-chemical calculations. Analysis of the P680+/P680 FTIR difference spectra of D1-V157H and D2-V156H showed that upon P680+ formation, the 131-keto C=O frequency upshifts by a much larger extent in PD1 (23 cm−1) than in PD2 (≪9 cm−1). In addition, thermoluminescence measurements revealed that the D1-V157H mutation increased the Em of P680 to a larger extent than did the D2-V156H mutation. These results, together with the previous results for the mutants of the His ligands of PD1 and PD2, lead to a definite conclusion that a charge is mainly localized to PD1 in P680+.

  • Effect of charge distribution over a chlorophyll dimer on the redox potential of P680 in photosystem II as studied by density functional theory calculations.
    Biochemistry, 2008
    Co-Authors: Ryouta Takahashi, Koji Hasegawa, T. Noguchi
    Abstract:

    The effect of charge distribution over a chlorophyll dimer on the redox potential of P680 in photosystem II was studied by density functional theory calculations using the P680 coordinates in the X-ray structure. From the calculated ionization potentials of the dimer and the monomeric constituents, the decrease in the redox potential by charge delocalization over the dimer was estimated to be approximately 140 mV. Such charge delocalization was previously observed in the isolated D1-D2-Cyt b 559 complexes, whereas the charge was primarily localized on P D1 in the core complexes. The calculated potential decrease of approximately 140 mV can explain the inhibition of Y Z oxidation in the former complexes and in turn implies that the charge localization on P D1 upon formation of the core complex increases the P680 potential to the level necessary for water oxidation.

  • Perturbation of the structure of P680 and the charge distribution on its radical cation in isolated reaction center complexes of photosystem II as revealed by fourier transform infrared spectroscopy.
    Biochemistry, 2007
    Co-Authors: Tatsunori Okubo, Tatsuya Tomo, Miwa Sugiura, T. Noguchi
    Abstract:

    The structure and the electronic properties of P680 and its radical cation in photosystem II (PSII) were studied by means of Fourier transform infrared spectroscopy (FTIR). Light-induced P680+/P680 FTIR difference spectra in the mid- and near-IR regions were measured using PSII membranes from spinach, core complexes from Thermosynechococcus elongatus, and reaction center (RC) complexes (D1-D2-Cytb559) from spinach. The spectral features of the former two preparations were very similar, indicating that the structures of P680 and its radical cation are virtually identical between membranes and cores and between plants and cyanobacteria. In sharp contrast, the spectrum of the RC complexes exhibited significantly different features. A positive doublet at ∼1724 and ∼1710 cm-1 due to the 131-keto CO stretches of P680+ in the membrane and core preparations were changed to a prominent single peak at 1712 cm-1 in the RC complexes. This observation was interpreted to indicate that a positive charge on P680+ was ext...

  • Fourier transform infrared study of the cation radical of P680 in the photosystem II reaction center: evidence for charge delocalization on the chlorophyll dimer.
    Biochemistry, 1998
    Co-Authors: T. Noguchi, Tatsuya Tomo, Yoriano Inoue
    Abstract:

    A Fourier transform infrared (FTIR) difference spectrum of the primary electron donor (P680) of photosystem II upon its photooxidation (P680+/P680) was obtained in the frequency region of 1000−3000...

G Christen - One of the best experts on this subject based on the ideXlab platform.

  • P680 reduction kinetics and redox transition probability of the water oxidizing complex as a function of ph and h d isotope exchange in spinach thylakoids
    Biochemistry, 1999
    Co-Authors: G Christen, And A Seeliger, G Renger
    Abstract:

    : The rise of fluorescence as an indicator for P680(+)* reduction by YZ and the period-four oscillation of oxygen yield induced by a train of saturating flashes were measured in dark-adapted thylakoids as a function of pH in the absence of exogenous electron acceptors. The results reveal that: (i) the average amplitude of the nanosecond kinetics and the average of the maximum fluorescence attained at 100 micros after the flash in the acidic range decrease with decreasing pH; (ii) the oxygen yield exhibits a pronounced period-four oscillation at pH 6.5 and higher damping at both pH 5.0 and pH 8.0; (iii) the probability of misses in the Si-state transitions of the water oxidizing complex is affected characteristically when exchangeable protons are replaced by deuterons [at pH 7.0 values of <1 are observed]. The results are discussed within the framework of a combined mechanism for P680(+)* reduction where the nanosecond kinetics reflect an electron transfer coupled with a "rocket-type" proton shift within a hydrogen bridge from YZ to a nearby basic group, X [Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431], and subsequent relaxations within a network of hydrogen bonds. It is concluded that in the acidic region the hydrogen bond between YZ and X (most likely His 190 of polypeptide D1) is interrupted either by direct protonation of X or by conformational changes due to acid-induced Ca2+ release. This gives rise to a decreased P680(+)* reduction by nanosecond kinetics and an increase of dissipative P680(+)* recombination at low pH. A different mechanism is responsible for the almost invariant amplitude of nanosecond kinetics and increase of alpha in the alkaline region.

  • The role of hydrogen bonds for the multiphasic P680(+)* reduction by YZ in photosystem II with intact oxyen evolution capacity. Analysis of kinetic H/D isotope exchange effects.
    Biochemistry, 1999
    Co-Authors: G Christen, Renger G
    Abstract:

    The mechanism of multiphasic P680(+)* reduction by YZ has been analyzed by studying H/D isotope exchange effects on flash-induced changes of 830 nm absorption, DeltaA830(t), and normalized fluorescence yield, F(t)/F0, in dark-adapted thylakoids and PS II membrane fragments from spinach. It was found that (a) the characteristic period four oscillations of the normalized components of DeltaA830(t) relaxation and of F(t)/F0 rise in the nanosecond and microsecond time domain are significantly modified when exchangeable protons are replaced by deuterons; (b) in marked contrast to the normalized steady-state extent of the microsecond kinetics of 830 nm absorption changes which increases only slightly due to H/D exchange (about 10%) the Si state-dependent pattern exhibits marked effects that are most pronounced after the first, fourth, fifth, and eighth flashes; (c) regardless of data evaluation by different fit procedures the results lead to a consistent conclusion, that is, the relative extent of the back reaction between P680(+)*QA-* becomes enhanced in samples suspended in D2O; and (d) this enhancement is dependent on the Si state of the WOC and attains maximum values in S2 and S3, most likely due to a retardation of the "35 micros kinetics" of P680(+)* reduction. In an extension of our previous suggestion on the functional role of hydrogen bonding of YZ by a basic group X (Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431), a model is proposed for the origin of the multiphasic P680(+)* reduction by YZ. Two types of different processes are involved: (a) electron transfer in the nanosecond time domain is determined by strength and geometry of the hydrogen bond between the O-H group of YZ and acceptor X, and (b) the microsecond kinetics reflect relaxation processes of a hydrogen bond network giving rise to a shift of the equilibrium P680(+)*YZ P680YZ(OX) toward the right side. The implications of this model are discussed.

  • the role of hydrogen bonds for the multiphasic P680 reduction by yz in photosystem ii with intact oxyen evolution capacity analysis of kinetic h d isotope exchange effects
    Biochemistry, 1999
    Co-Authors: G Christen, G Renger
    Abstract:

    The mechanism of multiphasic P680(+)* reduction by YZ has been analyzed by studying H/D isotope exchange effects on flash-induced changes of 830 nm absorption, DeltaA830(t), and normalized fluorescence yield, F(t)/F0, in dark-adapted thylakoids and PS II membrane fragments from spinach. It was found that (a) the characteristic period four oscillations of the normalized components of DeltaA830(t) relaxation and of F(t)/F0 rise in the nanosecond and microsecond time domain are significantly modified when exchangeable protons are replaced by deuterons; (b) in marked contrast to the normalized steady-state extent of the microsecond kinetics of 830 nm absorption changes which increases only slightly due to H/D exchange (about 10%) the Si state-dependent pattern exhibits marked effects that are most pronounced after the first, fourth, fifth, and eighth flashes; (c) regardless of data evaluation by different fit procedures the results lead to a consistent conclusion, that is, the relative extent of the back reaction between P680(+)*QA-* becomes enhanced in samples suspended in D2O; and (d) this enhancement is dependent on the Si state of the WOC and attains maximum values in S2 and S3, most likely due to a retardation of the "35 micros kinetics" of P680(+)* reduction. In an extension of our previous suggestion on the functional role of hydrogen bonding of YZ by a basic group X (Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431), a model is proposed for the origin of the multiphasic P680(+)* reduction by YZ. Two types of different processes are involved: (a) electron transfer in the nanosecond time domain is determined by strength and geometry of the hydrogen bond between the O-H group of YZ and acceptor X, and (b) the microsecond kinetics reflect relaxation processes of a hydrogen bond network giving rise to a shift of the equilibrium P680(+)*YZ P680YZ(OX) toward the right side. The implications of this model are discussed.

  • On the origin of the `35-μs kinetics' of P680+⋅ reduction in photosystem II with an intact water oxidising complex
    FEBS letters, 1998
    Co-Authors: G Christen, F. Reifarth, Gernot Renger
    Abstract:

    The origin of the `35-μs kinetics' of P680+⋅ reduction in photosystem II (PS II) with an intact water oxidising complex has been analysed by comparative measurements of laser flash induced changes of the 830-nm absorption and the relative quantum yield of chlorophyll (Chl) fluorescence. The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F., Christen, G. and Renger, G. (1997) Photosynth. Res. 51, 231–242]. It was found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted samples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35-μs kinetics under identical excitation conditions are strikingly different with maxima after the 3rd and 5th flash for the 830-nm absorption changes vs. pronounced maxima after the 4th and 8th flash for the rise of the fluorescence yield. The period four oscillations unambiguously show that the `35-μs kinetics' of P680+⋅ reduction are characteristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) indicates that in contrast to the ns components of P680+⋅ reduction the 35-μs kinetics do not reflect exclusively an electron transfer from YZ to P680+⋅. It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680+⋅ reduction by YZ and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield.

  • on the origin of the 35 μs kinetics of P680 reduction in photosystem ii with an intact water oxidising complex
    FEBS Letters, 1998
    Co-Authors: G Christen, F. Reifarth, G Renger
    Abstract:

    The origin of the `35-μs kinetics' of P680+⋅ reduction in photosystem II (PS II) with an intact water oxidising complex has been analysed by comparative measurements of laser flash induced changes of the 830-nm absorption and the relative quantum yield of chlorophyll (Chl) fluorescence. The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F., Christen, G. and Renger, G. (1997) Photosynth. Res. 51, 231–242]. It was found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted samples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35-μs kinetics under identical excitation conditions are strikingly different with maxima after the 3rd and 5th flash for the 830-nm absorption changes vs. pronounced maxima after the 4th and 8th flash for the rise of the fluorescence yield. The period four oscillations unambiguously show that the `35-μs kinetics' of P680+⋅ reduction are characteristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) indicates that in contrast to the ns components of P680+⋅ reduction the 35-μs kinetics do not reflect exclusively an electron transfer from YZ to P680+⋅. It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680+⋅ reduction by YZ and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield.