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'Absorbance Difference Spectra' in keywords Facet   Publication Year 1990  [X]
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1Author    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