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G. Renger - One of the best experts on this subject based on the ideXlab platform.
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two reaction pathways for transformation of high potential cytochrome b559 of ps ii into the intermediate potential form
Biochimica et Biophysica Acta, 2007Co-Authors: O P Kaminskaya, V A Shuvalov, G. RengerAbstract:Abstract This study describes an analysis of different treatments that influence the relative content and the midpoint potential of HP Cyt b559 in PS II membrane fragments from higher plants. Two basically different types of irreversible modification effects are distinguished: the HP form of Cyt b559 is either predominantly affected when the heme group is oxidized (“O-type” effects) or when it is reduced (“R-type” effects). Transformation of HP Cyt b559 to lower potential redox forms (IP and LP forms) by the “O-type” mechanism is induced by high pH and detergent treatments. In this case the effects consist of a gradual decrease in the relative content of HP Cyt b559 while its midpoint potential remains unaffected. Transformation of HP Cyt b559 via an “R-type” mechanism is caused by a number of exogenous compounds denoted L: herbicides, ADRY reagents and tetraphenylboron. These compounds are postulated to bind to the PS II complex at a quinone binding site designated as Q C which interacts with Cyt b559 and is clearly not the Q B site. Binding of compounds L to the Q C site when HP Cyt b559 is oxidized gives rise to a gradual decrease in the E m of HP Cyt b559 with increasing concentration of L (up to 10 K ox ( L ) values) while the relative content of HP Cyt b559 is unaffected. Higher concentrations of compounds L required for their binding to Q C site when HP Cyt b559 is reduced (described by K red ( L )) induce a conversion of HP Cyt b559 to lower potential redox forms (“R-type” transformation). Two reaction pathways for transitions of Cyt b559 between the different protein conformations that are responsible for the HP and IP/LP redox forms are proposed and new insights into the functional regulation of Cyt b559 via the Q C site are discussed.
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evidence for a novel quinone binding site in the photosystem ii ps ii complex that regulates the redox potential of cytochrome b559
Biochemistry, 2007Co-Authors: O P Kaminskaya, V A Shuvalov, G. RengerAbstract:The present study provides a thorough analysis of effects on the redox properties of cytochrome (Cyt) b559 induced by two photosystem II (PS II) herbicides [3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,4-dinitro-6-sec-butylphenol (dinoseb)], an acceleration of the deactivation reactions of system Y (ADRY) agent carbonylcyanide-m-chlorophenylhydrazone (CCCP), and the lipophilic PS II electron-donor tetraphenylboron (TPB) in PS II membrane fragments from higher plants. The obtained results revealed that (1) all four compounds selectively affected the midpoint potential (Em) of the high potential (HP) form of Cyt b559 without any measurable changes of the Em values of the intermediate potential (IP) and low potential (LP) forms; (2) the control values from +390 to +400 mV for HP Cyt b559 gradually decreased with increasing concentrations of DCMU, dinoseb, CCCP, and TPB; (3) in the presence of high TPB concentrations, a saturation of the Em decrease was obtained at a level of about +240 mV, whereas no...
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redox and spectral properties of cytochrome b559 in different preparations of photosystem ii
Biochemistry, 1999Co-Authors: O P Kaminskaya, Jens Kurreck, Klausd Irrgang, G. Renger, Vladimir A. ShuvalovAbstract:A detailed analysis of the properties of cytochrome b559 (Cyt b559) in photosystem II (PS II) preparations with different degrees of structural complexity is presented. It reveals that (i) D1−D2−Cyt b559 complexes either in solubilized form or incorporated into liposomes contain only one type of Cyt b559 with Em values of 60 ± 5 and 100 ± 10 mV, respectively, at pH 6.8; (ii) in oxygen-evolving solubilized PS II core complexes Cyt b559 exists predominantly (>85%) as an LP form with an Em,7 of 125 ± 10 mV and a minor fraction with an Em,7 of −150 ± 15 mV; (iii) in oxygen-evolving PS II membrane fragments three different redox forms are discernible with Em values of 390 ± 15 mV (HP form), 230 ± 20 mV (IP form), and 105 ± 25 mV (LP form) and relative amplitudes of 58, 24, and 18%, respectively, at pH 7.3; (iv) the Em values are almost pH-independent between pH 6 and 9.5 in all sample types except D1−D2−Cyt b559 complexes incorporated into liposomes with a slope of −29 mV/pH unit, when the pH increases from 6 ...
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interconversion of low and high potential forms of cytochrome b559 in tris washed photosystem ii membranes under aerobic and anaerobic conditions
Biochemistry, 1999Co-Authors: Rena Gadjieva, G. Renger, Fikret Mamedov, Stenbjorn StyringAbstract:In this study, the reversible conversion between the high- (HP) and low-potential (LP) forms of Cytb559 has been analyzed in Tris-washed photosystem II (PSII) enriched membranes. These samples are deprived of the Mn cluster of the water-oxidizing complex (WOC) and the extrinsic regulatory proteins. The results obtained by application of optical and EPR spectroscopy reveal that (i) under aerobic conditions, the vast majority of Cytb559 exhibits a low midpoint potential, (ii) after removal of O2 in the dark, a fraction of Cytb559 is converted to the high-potential form which reaches level of about 25% of the total Cytb559, (iii) a similar dark transformation of LP HP Cytb559 occurs under reducing conditions (8 mM hydroquinone), (iv) under anaerobic conditions and in the presence of 8 mM hydroquinone, about 60% of the Cytb559 attains the HP form, (v) the interconversion is reversible with the re-establishment of aerobic conditions, and (vi) aerobic and oxidizing conditions (2 mM ferricyanide or 0.5 mM potassium iridate) induce a decrease of the amount of the HP form, also showing that the conversion is reversible. This reversible interconversion between LP and HP Cytb559 is not observed in PSII membrane fragments with an intact WOC. On the basis of these findings, the possibility is discussed that the O2-dependent conversion of Cytb559 in PSII complexes lacking a functionally competent WOC is related to a protective role of Cytb559 in photoinhibition and/or that it is involved in the regulation of the assembly of a competent water-oxidizing complex in PSII. (Less)
O P Kaminskaya - One of the best experts on this subject based on the ideXlab platform.
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two reaction pathways for transformation of high potential cytochrome b559 of ps ii into the intermediate potential form
Biochimica et Biophysica Acta, 2007Co-Authors: O P Kaminskaya, V A Shuvalov, G. RengerAbstract:Abstract This study describes an analysis of different treatments that influence the relative content and the midpoint potential of HP Cyt b559 in PS II membrane fragments from higher plants. Two basically different types of irreversible modification effects are distinguished: the HP form of Cyt b559 is either predominantly affected when the heme group is oxidized (“O-type” effects) or when it is reduced (“R-type” effects). Transformation of HP Cyt b559 to lower potential redox forms (IP and LP forms) by the “O-type” mechanism is induced by high pH and detergent treatments. In this case the effects consist of a gradual decrease in the relative content of HP Cyt b559 while its midpoint potential remains unaffected. Transformation of HP Cyt b559 via an “R-type” mechanism is caused by a number of exogenous compounds denoted L: herbicides, ADRY reagents and tetraphenylboron. These compounds are postulated to bind to the PS II complex at a quinone binding site designated as Q C which interacts with Cyt b559 and is clearly not the Q B site. Binding of compounds L to the Q C site when HP Cyt b559 is oxidized gives rise to a gradual decrease in the E m of HP Cyt b559 with increasing concentration of L (up to 10 K ox ( L ) values) while the relative content of HP Cyt b559 is unaffected. Higher concentrations of compounds L required for their binding to Q C site when HP Cyt b559 is reduced (described by K red ( L )) induce a conversion of HP Cyt b559 to lower potential redox forms (“R-type” transformation). Two reaction pathways for transitions of Cyt b559 between the different protein conformations that are responsible for the HP and IP/LP redox forms are proposed and new insights into the functional regulation of Cyt b559 via the Q C site are discussed.
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evidence for a novel quinone binding site in the photosystem ii ps ii complex that regulates the redox potential of cytochrome b559
Biochemistry, 2007Co-Authors: O P Kaminskaya, V A Shuvalov, G. RengerAbstract:The present study provides a thorough analysis of effects on the redox properties of cytochrome (Cyt) b559 induced by two photosystem II (PS II) herbicides [3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,4-dinitro-6-sec-butylphenol (dinoseb)], an acceleration of the deactivation reactions of system Y (ADRY) agent carbonylcyanide-m-chlorophenylhydrazone (CCCP), and the lipophilic PS II electron-donor tetraphenylboron (TPB) in PS II membrane fragments from higher plants. The obtained results revealed that (1) all four compounds selectively affected the midpoint potential (Em) of the high potential (HP) form of Cyt b559 without any measurable changes of the Em values of the intermediate potential (IP) and low potential (LP) forms; (2) the control values from +390 to +400 mV for HP Cyt b559 gradually decreased with increasing concentrations of DCMU, dinoseb, CCCP, and TPB; (3) in the presence of high TPB concentrations, a saturation of the Em decrease was obtained at a level of about +240 mV, whereas no...
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redox and spectral properties of cytochrome b559 in different preparations of photosystem ii
Biochemistry, 1999Co-Authors: O P Kaminskaya, Jens Kurreck, Klausd Irrgang, G. Renger, Vladimir A. ShuvalovAbstract:A detailed analysis of the properties of cytochrome b559 (Cyt b559) in photosystem II (PS II) preparations with different degrees of structural complexity is presented. It reveals that (i) D1−D2−Cyt b559 complexes either in solubilized form or incorporated into liposomes contain only one type of Cyt b559 with Em values of 60 ± 5 and 100 ± 10 mV, respectively, at pH 6.8; (ii) in oxygen-evolving solubilized PS II core complexes Cyt b559 exists predominantly (>85%) as an LP form with an Em,7 of 125 ± 10 mV and a minor fraction with an Em,7 of −150 ± 15 mV; (iii) in oxygen-evolving PS II membrane fragments three different redox forms are discernible with Em values of 390 ± 15 mV (HP form), 230 ± 20 mV (IP form), and 105 ± 25 mV (LP form) and relative amplitudes of 58, 24, and 18%, respectively, at pH 7.3; (iv) the Em values are almost pH-independent between pH 6 and 9.5 in all sample types except D1−D2−Cyt b559 complexes incorporated into liposomes with a slope of −29 mV/pH unit, when the pH increases from 6 ...
Manuel Losada - One of the best experts on this subject based on the ideXlab platform.
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factors determining the special redox properties of photosynthetic cytochrome b559
FEBS Journal, 2001Co-Authors: Mercedes Roncel, Jose M. Ortega, Manuel LosadaAbstract:Factors controlling the redox properties of the two conventional forms of cytochrome b559, i.e. the unstable high-potential form and the stable low-potential form, have been further investigated using PSII-enriched membranes from pea and spinach chloroplasts. The redox potential of the stable form of cytochrome b559 is pH independent both above pH 7.5 (E′m ≈ +110 mV) and below pH 6.0 (E′m ≈+203 mV), but it changes with a slope of 58 mV per pH unit between these two pH values. Thus, cytochrome b559 seems to have a single ionizing group influencing its redox potential, with a higher affinity for protons in the reduced form (pKred = 7.5) and a lower affinity in the oxidized form (pKox = 6.0); consequently, one unprotonated low-potential form (LP) and one protonated intermediate-potential form (IP). The redox potential of the high-potential form (HP) is pH-independent between pH 5.0 and 8.0, but its relative content (compared to the total amount of protein) decreases progressively above pH 7.0. This conversion to the stable LP form is interpreted as corresponding to the loss of a proton by one ionizing group, the protonation of which is essential for maintaining the unstable HP state. According to chemical modification experiments with diethylpyrocarbonate, one of the two histidine ligands of the heme seems to be the ionizing group responsible for the existence of both the protonated IP and HP forms. It is proposed that the difference between the IP and HP forms is due to the formation of an additional hydrogen bond between the protonated histidine and the protein in the HP state that stabilizes a special hydrophobic heme environment responsible for its high redox potential.
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ph dependent photoreactions of the high and low potential forms of cytochrome b559 in spinach ps ii enriched membranes
Photosynthesis Research, 1995Co-Authors: Jose M. Ortega, Manuel Hervas, Miguel A. Rosa, Manuel LosadaAbstract:Cytochrome b559 (Cyt b559) is a well-known intrinsic component of Photosystem II (PS II) reaction center in all photosynthetic oxygen-evolving organisms, but its physiological role remains unclear. This work reports the response of the two redox forms of Cyt b559 (i.e. the high- (HP) and low-potential (LP) forms) to inhibition of the donor or acceptor side of PS II. The photooxidation of HP Cyt b559 induced by red light at room temperature was pH-dependent under conditions in which electron flow from water was diminished. This photooxidation was observed only at pH values higher than 7.5. However, in the presence of 1 μM CCCP, a limited oxidation of HP Cyt b559 was observed at acidic pH, At pH 8.5 and in the presence of the protonophore, this photooxidation of the HP form was accompanied by its partial transformation into the LP form. On the other hand, a partial photoreduction of LP Cyt b559 was induced by red light under aerobic conditions when electron transfer through the primary quinone acceptor QA was impaired by strong irradiation in the presence of DCMU. This photoreduction was enhanced at acidic pH values. To the best of our knowledge, this is the first time that both photoreduction and photooxidation of Cyt b559 is described under inhibitory conditions using the same kind of membrane preparations. A model accommodating these findings is proposed.
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redox properties of cytochrome b559 in photosynthetic membranes from the cyanobacterium synechocystis sp pcc 6803
Journal of Plant Physiology, 1994Co-Authors: Jose M. Ortega, Manuel Hervas, Miguel A. Rosa, Manuel LosadaAbstract:Summary Cytochrome b 559 (Cyt b 559) is an intrinsic and essential component of the photosystem II (PSII) reaction center, but its physiological function remains yet undefined. In this study, a partial redox characterization of Cyt b 559 in photosynthetic membranes from the transformable unicellular cyanobacterium Synecborystis sp. PCC 6803 (hereafter called Synecborystis 6803) has been performed. In thylakoid membranes extracted by a very mild cell-breaking procedure, as developed in this work, only one redox form of Cyt b 559 was found, with a redox potential proper to a low-potential (LP) form. The midpoint redox potential value of this LP form has been shown to be + 170 mV at pH 7.5 in PSII-enriched membranes. In spite of a great variety of cell-breaking treatments used to prepare thylakoid membranes, it has not been possible to detect any high-potential (HP) form of Cyt b 559. The absence of this HP form is discussed in terms of its higher lability in Synecborystis 6803 as compared with other cyanobacteria and higher plants. Alternatively, the possibility is considered that a HP form of Cyt b 559 does not occur in Synecborystis 6803 because it can not be properly stabilized in the membrane environment.
Dejan S Filipovic - One of the best experts on this subject based on the ideXlab platform.
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reduced size planar dual polarized log periodic antenna for bidirectional high power transmit and receive applications
IEEE Transactions on Antennas and Propagation, 2014Co-Authors: Rohit Sammeta, Dejan S FilipovicAbstract:An improved method of more than halving the turn on frequency of a 4-arm log-periodic (LP) antenna for dual-circularly polarized (CP) bidirectional use is demonstrated. The ground plane currents of a slot-LP are manipulated by varying “ground plane” shape to form a ring-turnstile-slot LP aperture and thus extend the overall antenna bandwidth. The proposed concept is used to design and fabricate an antenna that is 2.3 times smaller than the conventional 4-arm LP and works from 500 MHz to 3 GHz. Microstrip impedance transformer/balun is used to feed the LP thus allowing for bidirectional use and much simpler beamforming network for dual-polarized operation. VSWR and far-field behavior of the antenna are characterized and its high-power thermal stability is demonstrated through a high-power test. The advantages over the previously designed ring-turnstile-LP configuration are highlighted and the design principles undertaken to make the antenna high-power capable are illustrated. The prototyped antenna is meant not only to illustrate the proposed concept but also as a viable high-power bidirectional antenna.
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quasi frequency independent increased bandwidth planar log periodic antenna
IEEE Transactions on Antennas and Propagation, 2014Co-Authors: Rohit Sammeta, Dejan S FilipovicAbstract:A novel antenna composite with greatly extended bandwidth of a baseline printed 4-arm log-periodic (LP) topology is introduced. Bandwidth increase by accomplishing a miniaturization factor >2 is achieved by coupling the currents from the booms of the LP to an annular ring, thereby providing an efficient well-matched radiator at frequencies below the cut-off frequency of the LP. The annulus, the turnstile (booms of the LP), and the LP form the radiators of this novel quasi frequency-independent (FI) ring-turnstile-LP antenna. A 160 mm diameter antenna is designed and fabricated to demonstrate the proposed concept. Measured VSWR and extensive far-field characterization verify multi-octave dual circular polarization (CP) operation and a size reduction factor of 2.25. Also, the ring-turnstile-LP configuration is integrated with two planar impedance transformers/feeds to demonstrate small size, simple beamformer and dual-CP operation over bandwidths as wide as those of more complex sinuous and singly polarized spiral antennas. Detailed computational studies are conducted for better understanding the impact of various structural parameters on antenna's unidirectional performance and relevant conclusions are provided.
Thomas Villmann - One of the best experts on this subject based on the ideXlab platform.
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applications of lp norms and their smooth approximations for gradient based learning vector
2014Co-Authors: Mandy Lange, Dietlind Zuhlke, O Holz, Thomas VillmannAbstract:Learning vector quantization applying non-standard metrics became quite popular for classification performance improvement compared to standard ap- proaches using the Euclidean distance. Kernel metrics and quadratic forms belong to the most promising approaches. In this paper we consider Minkowski distances (Lp-Norms). In particular, l1-norms are known to be robust against noise in data, such that, if this structural knowledge is available in advance about the data, this norm should be utilized. However, application in gradient based learning algo- rithms based on distance evaluations need to calculate the respective derivatives. Because lp-distance formulas contain the absolute approximations thereof are re- quired. We consider in this paper several approaches for smooth consistent approx- imations for numerical evaluations and demonstrate the applicability for exemplary real world applications.
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applications of lp norms and their smooth approximations for gradient based learning vector quantization
The European Symposium on Artificial Neural Networks, 2014Co-Authors: Mandy Lange, Dietlind Zuhlke, O Holz, Thomas VillmannAbstract:Learning vector quantization applying non-standard metrics became quite popular for classification performance improvement compared to standard approaches using the Euclidean distance. Kernel metrics and quadratic forms belong to the most promising approaches. In this paper we consider Minkowski distances (Lp-Norms). In particular, l1-norms are known to be robust against noise in data, such that, if this structural knowledge is available in advance about the data, this norm should be utilized. However, application in gradient based learning algorithms based on distance evaluations need to calculate the respective derivatives. Because lp-distance formulas contain the absolute approximations thereof are required. We consider in this paper several approaches for smooth consistent approximations for numerical evaluations and demonstrate the applicability for exemplary real world applications.
