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'Phycoerythrin' in keywords
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1983 (1)
1980 (1)
1979 (1)
1Author    Hugo Scheer, Helmut Formanek, W. Olfhart RüdigerRequires cookie*
 Title    The Conformation of Bilin Chromophores in Biliproteins: Ramachandran-Type Calculations  
 Abstract    Ramachandran-type calculations are perform ed for conformations o f bilin chromophores pres­ ent in the biliproteins phycocyanin, phycoerythrin and phytochrome. The atom ic coordinates are taken from x-ray data o f crystalline model compounds, namely biliverdin for pyrrole rings B, C, D and substituted succinimides for the hydrogenated ring A including a thioether containing ^-sub­ stituent. Maxima and m inim a for steric hindrance are calculated for rotation o f the thioether side chain, the rotation of pyrrole rings at single bonds (syn-anti-forms) and at double bonds (Z-E-iso-mers) of the methine bridges. Whereas quasi-planar structures are possible for all syn, Z-forms, only twisted structures are possible if anti, E-forms are considered. The relevance for the bilin con­ formations of native biliproteins and o f the Pr ^ Pfr phototransform ation is discussed. 
  Reference    Z. Naturforsch. 34c, 1085 (1979); received June 29 1979 
  Published    1979 
  Keywords    Bilin Conformation, Phycocyanin, Phycoerythrin, Phytochrome 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-1085.pdf 
 Identifier    ZNC-1979-34c-1085 
 Volume    34 
2Author    Harald Lehner, Hugo ScheerRequires cookie*
 Title    Circulardichroism of C-Phycocyanin: Origin of Optical Activity in Denatured Biliproteins and Evidence for an Intermediate during Unfolding  
 Abstract    The circulardichroism spectra (cd) o f native and (partially) urea-denaturated C-phycocyanin (PC) in the spectral range 7 0 0 -2 1 0 nm are presented. The large ellipticities observed in the chrom ophoric region of native PC are retained in the fully denatured state (8 M urea). This is sim ilar to the behavior of the red form of phytochrome (Pc), but in contrast to C-phycoerythrin (PE). These differences are rationalized in terms of epim eric equilibria betw een P-and M-helix shaped chromophores. D epending on the num ber and location o f the chirality centers present in the tetrapyrrol moities a priori, the excess populations of the inherently chiral P-and M-helices differ, thus accounting for large (PC, Pr) or small (PE) ellipticities in the denatured pigments. Hence, the large optical activity observed for the form er is generated by an excess population of the P-helix induced by the asymmetric C-2, C-3 and C-3'. In PE the additional chirality center at C -l6 counteracts the influence of the others. The excess population o f the inherently chiral species is therefore lowered, in agreem ent with the nearly vanishing cd reported for denatured PE. The cd has also been studied at interm ediate urea concentrations. U nfolding of PC with urea can be interpreted from these data as a stepwise process. M onitoring the urea induced unfolding of PC by cd at different wavelengths (A = 220, 345, and 610 nm); the "melting po in t" o f the apoprotein (4 -5 M urea) coincides with the extrema of the titration curves obtained in the chrom ophore region (345, 610 nm). These results give direct evidence for the existence of an interm ediate species whose population reaches a m aximum at 4 — 5 M urea. 
  Reference    Z. Naturforsch. 38c, 353 (1983); received January 17 1983 
  Published    1983 
  Keywords    Phycocyanin, Phycoerythrin, Phytochrom, C irculardichroism, D enaturation 
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 TEI-XML for    default:Reihe_C/38/ZNC-1983-38c-0353.pdf 
 Identifier    ZNC-1983-38c-0353 
 Volume    38 
3Author    Elisabeth Langer, H. Arald Lehner, Wolfhart Rüdiger, Barbara Zickendraht, -W EndelstadtRequires cookie*
 Title    Circular Dichroism of C-Phycoerythrin: A Conformational Analysis  
 Abstract    An extensive study o f the chiroptical properties o f C-phycoerythrin and the a-and ^-subunits in the spectral region from 700 -200 nm is presented. Based on the VIS-circular dichroism inherently chiral conform ations are proposed for the co­ valently linked chromophores. By means o f mean residue ellipticities and the experimental circular dichroism spectra in the region o f the n -* n* peptide transition the a-helix contents o f the apoproteins o f the ac-and ß-subunits are estimated to amount to 60% and 40%, respectively. The circular dichroism spectrum o f native C-phycoerythrin is congruent with a linear superposition o f the a-and /?-subspectra, in the whole spectral region studied. Since a-and /?-subunits are associated in native C-phycoery-thrin as revealed by sedim entation analysis the interactions between the subunits in the native chromoprotein are not accom panied by substantial conform ational changes. In the temperature range 0 ° -4 0 °C the thermally induced changes o f the chrom ophores in native C-phycoerythrin are not associated with changes o f the secondary structure o f the apoprotein. Unfolding occurs at 60 0 -7 0 °C but slowly leads to irreversible denaturation. Protein unfolding starts at 3 M urea. The random coil secondary structure o f the apoproteins is reached at 8 M urea. At this concentration the absorbance and the optical activity o f the chrom o­ phores are reduced by a factor 3 and 10, respectively. The conformational changes in the peptide with increasing denaturant concentration are not synchronous with those induced in the Chromo­ phore indicating that a m ultistep process is operative during unfolding. The C D results on dena­ turation are supplem ented by absorption and em ission spectroscopy. 
  Reference    Z. Naturforsch. 35c, 367 (1980); received February 5 1980 
  Published    1980 
  Keywords    Phycoerythrin, Subunits, Conformation o f Chrom ophores and Apoproteins, Circular D ichroism, Denaturation 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0367.pdf 
 Identifier    ZNC-1980-35c-0367 
 Volume    35