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'Plastoquinone' in keywords Facet   Publication Year 1984  [X]
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1984[X]
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