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1993 (4)
1Author    Hiroyuki Koike, Yasuhiro Kashino, Kazuhiko SatohRequires cookie*
 Title    Interactions of Halogenated Benzoquinones with the Non-Heme Iron (Q40o) in Photosystem II  
 Abstract    Interactions o f halogenated benzoquinones with the acceptor side o f Photosystem (PS) II were studied by measuring fluorescence induction curves and flash-induced absorbance changes in PS II particles isolated from Synechococcus vulcanus. Following results were ob­ tained: 1) Addition o f some halogenated benzoquinones prior to 3-(3,4-dichlorophenyl)-l,l-dimethylurea (D C M U) in the dark increased the area above the fluorescence induction curve (work integral) by a factor o f two. 2) Based on the ability to increase the fluorescence work integral, halogenated benzoquinones could be divided into two groups. 3) 2,6-D ichlorobenzo-quinone (2,6-D C BQ), trichlorobenzoquinone (TCBQ) and tetrahalogenated benzoquinones except tetrafluorobenzoquinone (fluoranil) (group A) increased the work integral, but 2,5-D CBQ and fluoranil (group B) did not. 4) Rapid reoxidation o f QA was observed in the presence o f quinones which belong to group A. These results were interpreted in terms o f dark oxidation o f by quinones belonging to group A. Possible mechanisms o f oxidation o f Q400 by these quinones in the dark are discussed. 
  Reference    Z. Naturforsch. 48c, 168 (1993); received Novem ber 9 1992 
  Published    1993 
  Keywords    Photosystem II, Q400, Halogenated Benzoquinone, Q B-Site, Fluorescence Induction 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0168.pdf 
 Identifier    ZNC-1993-48c-0168 
 Volume    48 
2Author    Kazuhiko Satoh, Yasuhiro Kashino, Hiroyuki KoikeRequires cookie*
 Title    Electron Transport from QA to Thymoquinone in a Synechococcus Oxygen-Evolving Photosystem II Preparation: Role of QB and Binding Affinity of Thymoquinone to the QB Site  
 Abstract    We have recently shown that binding affinities o f benzoquinones can be estimated by two methods in photosystem (PS) II particles (K. Satoh et al., Biochim. Biophys. Acta 1 1 0 2 ,4 5 -5 2 (1992)). U sing these methods we calculated the binding affinity o f thym oquinone (2-methyl-5-isopropyl-/?-benzoquinone) to the Q B site and studied how the quinone accepts electrons in oxygen-evolving PS II particles isolated from the thermophilic cyanobacteria, Synechococcus elongatus and S. vulcanus. The results are as follows: (1) The binding constant o f thym oqui­ none to the Q B site determined by several methods was around 0.33 m M . (2) At low thym oqui­ none concentrations the quinone was supposed to accept electrons via QB-plastoquinone, whereas at high concentrations the quinone seemed to bind to the QB site and accept an elec­ tron directly from Q~A. Lower rates o f photoreduction o f the quinone at high concentrations were attributed to a slower turnover rate o f the quinone at the QB site than that o f endogenous plastoquinone. (3) A model for the function o f plastoquinone at the Q B site, which can explain all the results, was presented. According to this model, the plastoquinone molecule at the Q B site is not replaced by another plastoquinone molecule. Instead, it transfers electrons to pool plastoquinone molecules by turning over its head group but remaining its long side chain bound to the PS II complexes. 
  Reference    Z. Naturforsch. 48c, 174 (1993); received November 9 1992 
  Published    1993 
  Keywords    Q b Site, Photosystem II, Thym oquinone, Plastoquinone, Synechococcus 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0174.pdf 
 Identifier    ZNC-1993-48c-0174 
 Volume    48 
3Author    G. Renger, H. M. Gleiter, E. Haag, F. ReifarthRequires cookie*
 Title    Photosystem II: Thermodynamics and Kinetics of Electron Transport from Qa" to Q b(Q b' ) and Deleterious Effects of Copper(II)  
 Abstract    Studies on thermodynamics and kinetics o f electron transfer from QA~ to QB(QB") were per­ formed by m onitoring laser flash induced changes o f the relative fluorescence emission as a function o f temperature (220 K < T < 310 K) in isolated thylakoids and PS II membrane frag­ ments. In addition, effects o f bivalent metal ions on PS II were investigated by measuring conven­ tional fluorescence induction curves, oxygen evolution, manganese content and atrazine bind­ ing mostly in PS II membrane fragments. It was found: a) the normalized level o f the fluores­ cence remaining 10 s after the actinic flash (FJF0) steeply increases at temperatures below -1 0 to -2 0 °C, b) the fast phase o f the transient fluorescence change becomes markedly retard­ ed with decreasing temperatures, c) am ong different cations (Cu2+, Zn2+, Cd2+, N i2+, Co2+) only Cu2+ exhibits marked effects in the concentration range below 100 jim and d) Cu2+ decreases the normalized variable fluorescence, inhibits oxygen evolution and diminishes the affinity to atrazine binding without affecting the number o f binding sites. The content o f about four manganeses per functionally competent oxygen evolving complex is not changed by [Cu2+] < 70 |iM. Based on these findings it is concluded: i) a temperature dependent equilibrium between an inactive (I) and active (A) state o f QA~ reoxidation by Q b(Qb) is characterized by standard 
  Reference    Z. Naturforsch. 48c, 234 (1993); received November 23 1992 
  Published    1993 
  Keywords    Photosystem II, Q B-Site, Copper(II) Effects, Fluorescence, Oxygen Evolution 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0234.pdf 
 Identifier    ZNC-1993-48c-0234 
 Volume    48 
4Author    Ralf Kloos, Edward Stevens, Walter OettmeierRequires cookie*
 Title    Complete Sequence of One Copy of the psbA Gene from the Thermophilic Cyanobacterium Synechococcus elongatus  
 Abstract    One copy of the psbA. gene which codes for the photosystem II reaction center D-l protein from the thermophilic cyanobacterium Synechococcus elongatus has been sequenced. It is feas­ ible that a disulfide bridge between D-l Cys212 and D-2 Cys2I2 is reponsible for the thermo­ stability of the photosystem II reaction center from Synechococcus elongatus. 
  Reference    Z. Naturforsch. 48c, 799—802 (1993); received June 1/July 2 1993 
  Published    1993 
  Keywords    D-l Protein, Herbicide Binding Protein, Q B-Site, psbA Gene, Synechococcus elongatus 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0799.pdf 
 Identifier    ZNC-1993-48c-0799 
 Volume    48