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'Plastoquinone' in keywords
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1993 (2)
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1Author    W. Im, F. J. Vermaas, G. Ern O, R. Enger, J. A. Arles, RntzenRequires cookie*
 Title    Herbicide/Quinone Binding Interactions in Photosystem II  
 Abstract    Many inhibitors prevent the oxidation o f the primary electron-accepting quinone (Q A) by the secondary quinone (Q B) in photosystem II by displacem ent o f Q B from its binding site. On the other hand, plastoquinone-1 and 6-azido-5-decyl-2,3-dim ethoxy-/?-benzoquinone displace herbicides. Binding studies show the herbicide/quinone interaction to be (apparently) competitive. The herbicide binding is influenced differentially by various treatments. In this paper it is shown that the affinity of, for example, brom oxynil is decreased by thylakoid unstacking or by light-or reductant-induced reduction o f certain thylakoid com ponents, whereas atrazine affinity remains unchanged. Furthermore, absence o f H C O j in the presence o f form ate leads to an affinity decrease o f bromoxynil and atrazine, but to an increase in i-dinoseb affinity. Other differential photosystem II herbicide effects are known from the literature. Since different and unrelated groups o f Q A oxidation inhibitors have been found, and because o f the above-mentioned dissim ilarities in binding characteristics for different inhibitor groups, the hypothesis o f non-identical, but "overlapping" binding sites for different herbicide groups and the native quinone must be more extensively defined. In this m anuscript we evaluate both the competitive herbicide/quinone binding m odel, and a m odel in which binding o f one ligand alters the protein conformation resulting in a dram atic decrease in the binding affinity o f ligands from other chemical groups; in this model ligands from the sam e or related chem ical groups bind competitively. Thus, the latter model proposes that only one herbicide or quinone m olecule can be bound with high affinity to the herbicide/quinone binding environm ent, but it depends on the chemical structure o f the ligands whether the binding interaction betw een two ligands is truly competitive or more indirect (allosteric), m ediated through the protein conform ation. 
  Reference    Z. Naturforsch. 39c, 368 (1984); received D ecem ber 1 1983 
  Published    1984 
  Keywords    Herbicide, Photosystem II, Plastoquinone, Photosynthesis, A llosteric interaction 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0368.pdf 
 Identifier    ZNC-1984-39c-0368 
 Volume    39 
2Author    HowardH R Obinson, JulianJ E Aton-R, Ye, JackJ S Van, R. Ensen, G. OvindjeeRequires cookie*
 Title    The Effects of Bicarbonate Depletion and Formate Incubation on the Kinetics of Oxidation-Reduction Reactions of the Photosystem II Quinone Acceptor Complex  
 Abstract    Chloroplast thylakoid membranes depleted o f bicarbonate exhibit a slowed oxidation o f the primary quinone acceptor (QA) by the secondary quinone acceptor (Q B) o f photosystem II. The kinetics o f these slowed reactions have been follow ed by using short xenon flashes o f light both to excite photosystem II and to probe the redox state o f Q A. Thylakoids incubated with formate but not depleted o f bicarbonate showed the sam e pattern o f slowed reaction kinetics o f the quinone acceptors as seen in bicarbonate-depleted thylakoids. This led us to conclude that there was a simple com petition between bicarbonate and formate at this site; however, steady-state electron transfer measured with an oxygen electrode showed that although the bicarbonate-depleted thylakoids were indeed inhibited, rates in the form ate-incubated thylakoids were only slightly slowed. We suggest that the inhibition seen at the quinone acceptor site o f photosystem II depends in a subtle way upon the rate o f exchange o f bicarbonate and formate at this site. 
  Reference    Z. Naturforsch. 39c, 382 (1984); received N ovem ber 14 1983 
  Published    1984 
  Keywords    Chloroplasts, Photosystem II, Bicarbonate, Formate, Plastoquinone 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0382.pdf 
 Identifier    ZNC-1984-39c-0382 
 Volume    39 
3Author    A. Trebst, W. D. Onner, W. D. RaberRequires cookie*
 Title    Structure Activity Correlation of Herbicides Affecting Plastoquinone Reduction by Photosystem II: Electron Density Distribution in Inhibitors and Plastoquinone Species  
 Abstract    Molecular orbital calculations o f the net charge and the n charge distribution in several inhibitors and herbicides o f the functionally related group o f the diuron and dinoseb type are reported. They confirm the m odel that urea, am inotriazinone and triazine herbicides all have in common a positive ^-charge at a particular atom considered to be essential for binding. Phenol type inhibitors have different charge distribution and a m odel for their essential features is presented. The calculations support the finding that two different subunits with different binding characteristics are involved in inhibitor and plastoquinone function on the acceptor side o f photosystem II. Force-field model building and MO calculations o f the charge distribution o f a plastoquinone analogue with a butenyl side chain, o f two o f its sem iquinone forms and o f the hydroquinone, are reported, as well as their conform ation with the lowest energy content and their likely anionic forms. 
  Reference    Z. Naturforsch. 39c, 405—411 (1984); received D ecem ber 23 1983 
  Published    1984 
  Keywords    Herbicides, Plastoquinone, MO Calculation, Photosystem II 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0405.pdf 
 Identifier    ZNC-1984-39c-0405 
 Volume    39 
4Author    Wim Vermaas, Jeroen Charité, Gaozhong ShenRequires cookie*
 Title    Q a Binding to D2 Contributes to the Functional and Structural Integrity of Photosystem II  
 Abstract    Two D 2 mutants were created with a site-directed mutation near the presumable binding site of Q a. In one of the mutants, in which Trp-253, the aromatic residue potentially involved in facilitating electron transport from pheophytin to Q A and/or in binding of Q A, had been replaced by Leu, PS II was undetectable in thylakoids. This mutant is an obligate photohetero-troph. In another mutant the Gly-215 residue, located next to the His residue that is pro­ posed to bind Q a and Fe2+, was mutated to Trp. This mutation leads to a rapid inactivation of oxygen evolution capacity in the light, and to a virtual elimination of the potential to grow photoautotrophically, but does not greatly affect the number of photosystem II reaction cen­ ters on a chlorophyll basis. We propose that proper binding of Q A to the photosystem II reac­ tion center complex is a prerequisite for stability of the photosystem II complex. Impairment of Q a binding leads to rapid inactivation of photosystem II, which may be followed by a struc­ tural disintegration of the complex. 
  Reference    Z. Naturforsch. 45c, 359—365 (1990); received November 3 1989 
  Published    1990 
  Keywords    Photoinhibition, Plastoquinone, Photosynthesis, Site-Directed Mutagenesis, Cyanobacteria 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0359.pdf 
 Identifier    ZNC-1990-45c-0359 
 Volume    45 
5Author    H. Adar Kless3, Michal Oren-Shamirb, ItzhakO. Hadc, M. Arvin Edelm, Wim VermaasaRequires cookie*
 Title    Protein Modifications in the D 2 Protein of Photosystem II Affect Properties of the Q B/Herbicide-Binding Environment  
 Abstract    The D 2 protein contains an extended loop (the D-de loop) between helices D and de at the reducing side o f photosystem II (PS II). Characterization o f D 2 mutants o f the cyanobacte­ rium Synechocystis sp. PCC 6803 has indicated that the length and amino acid com position o f the D-de loop are not critical for basic PS II functions, although most o f the residues in that region are conserved phylogenetically. Here we show using herbicide binding and electron-flow inhibition measurements that drastic modifications in the D-de loop o f the D 2 protein modify the interaction o f some PS II-directed herbicides with their binding niche. The stability o f (semi-)reduced Q B in its binding pocket is altered in at least two o f the mutants, as indicated by a shifted peak temperature o f the thermoluminescence signal originating from charge recombi­ nation involving QB. These results suggest a close functional association between the D-de loop o f the D 2 protein and the Q B/herbicide-binding environment, which is viewed as being coordinated mostly by re­ sidues o f the D 1 protein. This represents one o f the first examples o f m odification o f the Q B/ herbicide-binding domain by mutations in the D 2 protein. 
  Reference    Z. Naturforsch. 48c, 185—190 (1993); received November 23 1992 
  Published    1993 
  Keywords    Herbicides, Plastoquinone, Photosystem II, Thermoluminescence, Cyanobacteria 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0185.pdf 
 Identifier    ZNC-1993-48c-0185 
 Volume    48 
6Author    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