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'Herbicide Resistance' in keywords Facet   Publication Year 1993  [X]
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1993[X]
1Author    Sophie Creuzet, TeresaM. Iranda, Jean-M Arc DucruetRequires cookie*
 Title    Comparison of Experimental and Calculated Hydrogen Bonding Properties of Some Urea and Triazine Inhibitors of Photosystem II  
 Abstract    Previous studies o f structure/activity relationships o f photosystem II inhibitors, including com parisons o f their inhibitory power in herbicide-resistant and susceptible chloroplasts, have led to predict the role o f hydrogen bonding, associated to hydrophobicity, in the binding onto the Qb site. The crystallographic structures o f bacterial reaction centers now allow these bonds to be identified. In order to be able to understand the binding o f various herbicides and the effects o f resistance mutations within the Q B site, a reliable estimation o f hydrogen bonding strengths is needed. We show here, by calculating interactions with model com pounds, con ­ trolled by physicochemical measurements, that the hydrogen bonding properties o f the C = X nucleophilic moiety present in most PS II inhibitors are different for triazines as compared to urea or amide derivatives. Semiempirical methods (AM 1) fail to reproduce the energies o f hy­ drogen bonds between a triazine ring nitrogen and a phenolic proton. An empirical method (SI BFA), designed to reproduce interaction energies, has been adapted with the aim o f calculat­ ing the binding energies o f various herbicides with models o f the Q B site. 
  Reference    Z. Naturforsch. 48c, 179 (1993); received November 12 1992 
  Published    1993 
  Keywords    Herbicide, Herbicide Resistance, Hydrogen Bonding, M olecular Calculation, Photosystem II 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0179.pdf 
 Identifier    ZNC-1993-48c-0179 
 Volume    48 
2Author    Z. NaturforschRequires cookie*
 Title    Kinetics of Electron Transfer between Q A and Q B in Wild Type and Herbicide-Resistant Mutants of Chlamydomonas reinhardtii  
 Abstract    A n ton y R . C ro fts*, Irene B aroli, D avid K ra m e r, and Shinichi T a o k a Biophysics Division and *D epartm ent o f M icrobiology, University o f Illinois at U rbana-Cham paign, U rb ana, We have investigated the electron transfer kinetics for reduction o f plastoquinone by photo­ system II in six m utant strains o f Chlamydomonas reinhardtii by following the decay o f the high fluorescence state after flash activation, and com pared the separate reactions of the two-electron gate with those o f a wild type strain. By analysis o f the electron transfer kinetics, and separate measurement o f the equilibrium constant for stabilization o f the bound semiquinone after one flash, we have been able to deconvolute the contributions o f rate constants and equi­ librium constants for plastoquinone binding and electron transfer to the overall process. Two mutations, S 264 A and A 251 V, led to a marked slowing o f kinetics for reduction of plastoqui­ none to the bound semiquinone. In S 2 6 4 A , the second electron transfer was also slower, but was normal in A 2 5 1 V. In m utant G 2 5 6 D , the electron transfer kinetics were normal after the first flash, but slowed after the second. In mutants L 2 5 7 F , V 2 1 9 I, and F 2 5 5 Y , the electron transfer kinetics after both flashes were similar to those in wild type. We discuss the results in terms of a model which provides a description o f the mechanism o f the two-electron gate in terms of measured kinetic and equilibrium constants, and we give values for these parameters in all strains tested. 
  Reference    Z. Naturforsch. 48c, 259 (1993); received December 10 1992 
  Published    1993 
  Keywords    Electron Transfer, Kinetics, Tw o-Electron G ate, Herbicide Resistance, Photosystem II 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0259.pdf 
 Identifier    ZNC-1993-48c-0259 
 Volume    48