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'Electrochromism' in keywords Facet   section ZfN Section C  [X]
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1980 (1)
1979 (1)
1977 (1)
1Author    Kai-Udo Sewe, Roland ReichRequires cookie*
 Title    The Effect of Molecular Polarization on the Electrochromism of Carotenoids * II. Lutein-Chlorophyll Complexes: The Origin of the Field-Indicating Absorption-Change at 520 nm in the Membranes of Photosynthesis  
 Abstract    Electrochromic spectra of monolayers of carotenoids (lutein and ß -carotene) in contact with monolayers of chlorophylls and of pheophytin a are measured in thin capacitors. A specific inter­ action of one of the OH-groups of lutein with the Mg-atom of chlorophyll is found. The formation of this oriented complex accounts for the fact that a part of the electrochromic absorption-change of lutein depends linearly on the electric field strength, whereas for lutein alone only a smaller, quadratic electrochromism is found. In the preparation with chlorophyll a, the maximum of this linear electrochromism is located at shorter wavelengths (512 nm) than in the preparation with chlorophyll b (517 nm). The permanent field that has been postulated in photosynthetic membranes (to explain the linear dependence of the field-indicating absorption-changes of the carotenoids) may also be at­ tributed to such a complex formation with chlorophylls. Especially, the field-indicating absorption-change at 520 nm can now be attributed mainly to a lutein-chlorophyll b complex. The absorption-change at 520 nm, calculated according to this model from the present experiments in vitro, is of the same order of magnitude as observed in vivo. Furthermore, this model agrees with the hitherto unexplained observation that in chlorophyll-b-lacking mutants the absorption-change at 520 nm is smaller than in normal plants, and the maximum is located at shorter wavelengths. Besites, it is concluded that lutein is mainly located in the regions of photosystem II. The contributions of the other carotenoids (especially of neoxanthin) to the spectrum of the field-indicating absorption-changes are also discussed. From the above model, some conclusions are drawn on the asymmetrical arrangement of the different pigments in the membrane of photosynthesis: The bulk chlorophyll molecules that serve as complex partners for the carotenoids should be located near to the inner surface of the thylakoid membrane, and the carotenoids attached to these chlorophylls should be located more to the out­ side. The phytol chain of a chlorophyll molecule should form an acute angle with the plane of the porphyrin ring. 
  Reference    (Z. Naturforsch. 32c, 161—171 [1977]; received January 20 1977) 
  Published    1977 
  Keywords    Electrochromism, Carotenoids, Molecular Complexes, Biological Membranes, Photosynthesis 
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 TEI-XML for    default:Reihe_C/32/ZNC-1977-32c-0161.pdf 
 Identifier    ZNC-1977-32c-0161 
 Volume    32 
2Author    G. Renger, D. Difiore, B. Luuring, P. GräberRequires cookie*
 Title    The Variation of the Electrochromic Difference Spectrum at Various Stages of the Chloroplast Developm ent+  
 Abstract    The flash-induced difference spectrum in the range of 450 — 550 nm of protochloroplasts isolated from pea-leaves greened under intermittent illumination (2 min light, 98 min dark) was measured and compared with that of fully developed chloroplasts from pea leaves. Because of the sensitivity of the decay o fthe absorption changes to the ionophore valinomycin they were shown to mainly be due to an electrochromic bandshift of the membrane pigments (chlorophylls-a, -b and caro-tenoids). The differences in the shape and the amplitude between both spectra are consistently explained within the framework of a recent hypothesis supposed by Sewe and Reich (Z. Natur-forsch. 33 c, 161 — 171 (1978)) by the lack of chlorophyll-b in the protochloroplasts. It is con­ cluded, that the transformation of the protochloroplasts into chloroplasts which is accompanied by the incorporation of the light harvesting complex and the formation of grana stacks does not seriously change the orientation of the field indicating pigments within the membrane with respect of the polarity of the light induced vectorial electron transport. 
  Reference    Z. Naturforsch. 34c, 120 (1979); received October 23 1978 
  Published    1979 
  Keywords    Chloroplast Development, Electric Field, Electrochromism, Pigment Orientation 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-0120.pdf 
 Identifier    ZNC-1979-34c-0120 
 Volume    34 
3Author    Marc Symons, Anthony CroftsRequires cookie*
 Title    Flash-Induced Electrochromic Band Shifts, is It a Simple Mechanism?  
 Abstract    The flash-induced carotenoid bandshifts have been studied for various strains of both Rho-dopseudomonas sphaeroides and capsulata. A technique for calculating shifts o f isobestic points down to 0.05 nm is described. To this end, special attention has been paid to the appropriate cor­ rection for reaction center absorbance changes occuring concommitantly with the carotenoid bandshifts. Plots of the wavelength o f the isobestic point versus the corresponding absorption changes at the maximum o f the difference spectrum have been made, suggesting the existence o f different pools of carotenoids. The various pools of carotenoids seem to have different sizes, in­ ducing non-linearities in the plots. In some cases spectral differences of the pools have to be assumed. A possible interpretation o f the results would be that each electrogenic span of the electron transport chain is to be associated with its own pool of carotenoids, all the pools behaving in somewhat independant way. We discuss possible difficulties in making those measurements. 
  Reference    Z. Naturforsch. 35c, 139—144 (1980); received August 16 1979 
  Published    1980 
  Keywords    Electrochromism, Carotenoids, Electron Transport, Membrane Potential, Photosynthesis 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0139.pdf 
 Identifier    ZNC-1980-35c-0139 
 Volume    35