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'Photosystem II' in keywords Facet   section ZfN Section C:Volume 045  [X]
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1990 (7)
1Author    John Bowyer1, Mark Hiltonb, Julian Whitelegge3, Philip Jewess6, Patrick Camillerib, Antony Croftsc, Howard RobinsoncRequires cookie*
 Title    Molecular Modelling Studies on the Binding of Phenylurea Inhibitors to the D 1 Protein of Photosystem II  
 Abstract    A hypothetical molecular model of part of the D 1 protein of photosystem II, based on the analogous portion of the L subunit of the Rhodopseudomonas viridis reaction centre, has been used to study the binding of an extended hydrophobic phenylurea inhibitor (N,N-dimethyl-carbamoyl)4 -amino-4 '-chloro-rra«5 -stilbene) (I) to the Q B site. The inhibitor was fitted by eye into a cleft in the site, and a limited part of the inhibitor/D 1 complex was energy minimized. The gross orientation of the inhibitor placed the dimethylurea moiety towards the predicted binding domain of the plastoquinone head group, and the stilbene moiety directed along the quinone isoprenoid side chain binding domain, suggesting a similar pathway of approach of the two molecules from the membrane into the binding site. Binding interactions of the inhibi­ tor included hydrogen bonds to the side chain hydroxyl of ser 264 and the peptide carbonyl group of ala 251, with the side chain hydroxyl of ser 268 as an alternative ligand. Numerous hydrophobic contacts were also possible. Although phenylureas do not bind to reaction centres of Rp. viridis, many of the binding interactions to D 1 could also be detected in Rp. viridis. However, the ß-CH2 and 5-C02-groups of glu 212 in Rp. viridis are located in the corresponding region of D 1 occupied by the dimethylurea moiety of the inhibitor in our model of its binding to D 1. This may explain why diuron (D C M U) does not bind to Rp. viridis reac­ tion centres. 
  Reference    Z. Naturforsch. 45c, 379—387 (1990); received November 23 1989 
  Published    1990 
  Keywords    Phenylureas, Photosystem II, D 1 Protein, Molecular Modelling 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0379.pdf 
 Identifier    ZNC-1990-45c-0379 
 Volume    45 
2Author    HelenG M Cfadden, JohnN. PhillipsRequires cookie*
 Title    Synthesis and Use of Radiolabelled Cyanoacrylate Probes of the Photosystem II Herbicide Binding Site  
 Abstract    Cyanoacrylates are potent inhibitors o f photosynthetic electron transport (PET) and are po­ tentially useful probes o f the photosystem II herbicide binding site. A series o f cyanoacrylates was synthesized and the Hill inhibition activities evaluated in order to select com pounds suita­ ble for radioactive synthesis. A cyanoacrylate, 2-(2-nitrophenoxy)ethyl 3-benzylamino-2-cyano-2-pentenoate, was found to displace diuron from the photosystem II herbicide binding site. For this compound the dissociation constant o f the inhibitor/binding site complex was found to be 2 x 10"8 M with an active site concentration o f 2 nm ol/m g chlorophyll. In a similar system the corresponding figures for diuron were 1.2 x 10"8 m and 1.3 nm ol/m g chlorophyll. Photoaffinity labelling o f 1% II thylakoid proteins with 2-(2-azidophenoxy)ethyl 3-[7-l4C]-benzylam ino-2-cyano-2-pentenoate showed weak binding in the 32 and 28 kD mass regions, consistent with binding to the D, peptide. 
  Reference    Z. Naturforsch. 45c, 196—202 (1990); received September 20/N ovem ber 10 1989 
  Published    1990 
  Keywords    Cyanoacrylate, Photoaffinity Labelling, Photosystem II, Com petitive Inhibition, Diuron 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0196.pdf 
 Identifier    ZNC-1990-45c-0196 
 Volume    45 
3Author    JeffA. Nemson, Anastasios MelisRequires cookie*
 Title    Light-Induced Oxidation-Reduction Reactions of Photosystem II in Dichlorophenyl-dimethyl Urea (DCM U) Inhibited Thylakoids  
 Abstract    Illumination o f thylakoid membranes in the presence o f 3-(3',4'-dichlorophenyl)-1,1-di-methyl urea (D C M U) causes the reduction o f the primary quinone acceptor QA o f photosys­ tem II (PS II) and the storage o f a positive charge on the donor side o f the photochem ical reac­ tion center. These oxidation-reduction reactions are accompanied by characteristic changes o f absorbance in the ultra-violet region o f the spectrum. The PS II-related absorbance difference spectra (2 5 0 -3 5 0 nm) were compared in control and hydroxylamine-treated thylakoid mem­ branes, and in thylakoids suspended in the presence o f carbonyl cyanide-/7-(trifluoromethoxy)-phenylhydrazone (FCCP). The light minus dark difference spectra were dominated by the QA minus QA difference spectrum. Qualitatively, the three spectra were identical in the 3 0 0 -3 5 0 nm region, however, they showed distinct differences in the 2 5 0 -3 0 0 nm region. The latter arose because o f different contributions from the donor side o f PS II in the thylakoid membrane o f the three samples. The result suggested that FCCP acts as the ultimate electron donor in D C M U -poisoned chloroplasts. Therefore, the absorbance difference spectrum in the presence o f FCCP reflected a contribution from the QA minus QA com ponent only. D econvolu­ tion o f the absorbance difference spectra o f control and hydroxylamine-treated thylakoids yielded difference spectra attributed to the oxidation o f a com ponent on the donor side o f PS II. This com ponent did not conform with the known M n(III) — ■ > M n(IV) transition. R ath­ er, it indicated the oxidation o f a modified form o f Mn in the presence o f D C M U , probably a Mn(II) —> M n(III) transition. The results are discussed in terms o f the use o f D C M U -poisoned thylakoid membranes in the quantitation o f the primary quinone acceptor Q A by spectro-photom etric approaches. 
  Reference    Z. Naturforsch. 45c, 258 (1990); received July 25/August 21. 1989 
  Published    1990 
  Keywords    Absorbance Difference Spectra, Photosystem II, Electron Transport, Primary Quinone Acceptor, Electron D onor Tyrosine 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0258.pdf 
 Identifier    ZNC-1990-45c-0258 
 Volume    45 
4Author    R. Fromme, G. RengerRequires cookie*
 Title    Studies on Herbicide Binding in Photosystem II Membrane Fragments from Spinach  
 Abstract    The mechanism of atrazine binding and its modification by Chelex-100-induced Ca2+ deple­ tion and proteolytic degradation by trypsin, was analyzed in PS II membrane fragments from spinach. It was found: 1) Chelex-100 treatment leads in a comparatively slow process (/, 2 = 5 — 10 min) to Ca2+ re­ moval from a site that is characterized by a high affinity as reflected by K u values of the order of 10 7 M. The number of these binding sites was found to be almost one per PS II in samples washed twice with Ca2+ -free buffer. 2) Chelex-100 treatment does not affect the affinity of atrazine binding but increases the susceptibility to proteolytic attack by trypsin. 3) The electron transport activity is only slightly affected by Chelex-100 treatment. 4) The atrazine binding exhibits a rather small T-dependence within the physiological range of 7 °C to 27 °C. The implications of these findings for herbicide binding are discussed. 
  Reference    Z. Naturforsch. 45c, 373—378 (1990); received November 15 1989 
  Published    1990 
  Keywords    Atrazine Binding, Photosystem II, Ca2+ Effects, Temperature Dependence, Mild Proteolysis 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0373.pdf 
 Identifier    ZNC-1990-45c-0373 
 Volume    45 
5Author    HimadriB. Pakrasi, KarinJ. Nyhus, HowardG. RanokRequires cookie*
 Title    Targeted Deletion Mutagenesis of the ß Subunit of Cytochrome b559 Protein Destabilizes the Reaction Center of Photosystem II  
 Abstract    Oligonucleotide-directed mutagenesis techniques were used to delete the psbF gene, encod­ ing the ß subunit o f the cytochrom e b559 protein o f the photosystem II com plex in the cyano­ bacterium, Synechocystis 6803. Cyt b559 is an integral com ponent o f PS II complex. However, its precise functional role in PS II remains to be determined. Previously, we created a mutant in which the psbF gene as well as three o f its neighbouring genes, psbE , psbL and p sb i were simultaneously deleted from the chrom osom e o f Synechocystis 6803 (Pakrasi, Williams and Arntzen, EMBO J. 7, 3 2 5 -3 3 2 , 1988). This mutant had no PS II activity. However, the role o f any one o f the four individual gene products could not be determined by studying this mutant. The newly generated mutant, T 256, had only one gene, p sbF , deleted from the genome. This mutant was also impaired in its PS II activities. In addition, it had barely detectable levels o f two other protein com ponents, D1 (herbicide binding protein) and D2, o f the reaction center o f PS II, in its thylakoid membranes. In contrast, two other proteins o f PS II, CP47 and CP43 were present in appreciable amounts. Fluorescence spectra (77 K) o f the mutant showed the absence o f a peak at 695 nm that was previously believed to originate from CP47. In addition, phycobilisomes, the light-harvesting antenna system o f PS II, were found to be assembled normally in this mutant. We conclude that the presence o f the ß subunit o f Cyt b559 in the thylakoid membranes is critically important for the assembly o f PS II reaction center. 
  Reference    Z. Naturforsch. 45c, 423 (1990); received November 21 1989 
  Published    1990 
  Keywords    Photosystem II, Cytochrom e b559, Site-Directed Mutagenesis, Protein Complex Stability, Synechocystis 6803 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0423.pdf 
 Identifier    ZNC-1990-45c-0423 
 Volume    45 
6Author    MarcelA K Jansen, Klaus PfisterRequires cookie*
 Title    Conserved Kinetics at the Reducing Side of Reaction-Center II in Photosynthetic Organisms; Changed Kinetics in Triazine-Resistant Weeds  
 Abstract    The decay o f chlorophyll variable fluorescence after a "single turnover" flash is generally assumed to represent the reoxidation o f the reduced quinone Qa. We have observed that the kinetics o f this decay are very similar in a wide variety o f species. Comparing 28 different spe­ cies, we found an average half decay time o f 314 ± 4 6 (isec. N o systematic correlations were found between the decay rate and biochemical or physiological specializations such as C 2, C 4 or C A M . This indicates that structural as well as functional factors controlling photosystem II electron transfer between Qa and Qb are highly conserved. Apparently, the freedom for natural structural variations in this region is very limited. Triazine resistant plants, characterized by an altered amino acid sequence o f the D 1 protein, have clearly decreased rates o f Qa/Q b electron transfer. We found an average half decay time o f 946 ± 100 jisec (5 species). However, this three-fold decrease is much less than previously re­ ported. Therefore, if alterations o f photosystem II electron transfer efficiency contributes to an often reported reduction o f "ecological fitness", this contribution is smaller than was hitherto assumed. 
  Reference    Z. Naturforsch. 45c, 441—4 (1990); received November 27 1989 
  Published    1990 
  Keywords    Chlorophyll Fluorescence, Evolution, Photosystem II, Triazine Resistance, p sb A Conservation 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0441.pdf 
 Identifier    ZNC-1990-45c-0441 
 Volume    45 
7Author    Jack Dekker, RonaldG. BurmesterRequires cookie*
 Title    Differential Pleiotropy in a psbA Gene Mutant of Brassica napus Implies Altered Temporal Photosynthesis and Thermal Tolerance  
 Abstract    Studies were conducted to test the hypothesis that the mutation to the psbA. plastid gene that confers s-triazine resistance (R) also results in an altered diurnal pattern o f photosynthetic car­ bon reduction (CER) relative to that o f the susceptible (S) wild-type. In all experiments CER approximated the increasing and decreasing light levels during the diurnal. S C ER exceeded that o f R during the midday period, but R CER was greater early and late in the diurnal at 25 °C. R CER exceeded that o f S for most o f the diurnal at 35 °C and in older, crowded, nitrogen-starved plants. These studies support the stated hypothesis and indicate a more complex model o f photosynthetic productivity than previously observed. An assessment o f the photosynthetic competence o f either biotype may be a function o f the time o f day or the environmental condi­ tions the plants are exposed to, especially temperature. 
  Reference    Z. Naturforsch. 45c, 474 (1990); received October 18 1989 
  Published    1990 
  Keywords    Photosystem II, D -l Protein, Electron Transport, C hronobiology, Diurnal Rhythms 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0474.pdf 
 Identifier    ZNC-1990-45c-0474 
 Volume    45