The chromophore structure and chromophore-protein interactions in C-phycocyanin as studied by resonance Raman spectroscopy

Balázs Szalontai, Zoltán Gombos, Vilmos Csizmadia, Marc Lutz

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We have studied the changes occurring in the electronic absorption and resonance Raman spectra of C-phycocyanin from Synechococcus 6301 (Anacystis nidulans) during denaturation of the protein induced by lowering the pH of the medium. Absorption studies showed that phycocyanobilin probably does not change its native, extended conformation in the pH range 7.5-3.0, but folds into a helical conformation as the pH is lowered further. Resonance Raman spectra obtained using ultraviolet excitation at 363.8 nm and at low temperature (40 K) revealed that non-covalent chromophore-protein interactions which are necessary in maintaining the extended conformation of the phycocyanobilin chromophore in the native protein involve the ends of the chromophore. They probably involve strong interactions from the protein on the two lactam C=O groups. These groups indeed become protonated only at pH values lower than 2.7, hence allowing folding of the chromophore. At pH 1.5 a complete denaturation of the protein occurs, but even this is partly reversible upon restoration of the physiological pH values.

Original languageEnglish
Pages (from-to)296-304
Number of pages9
JournalBBA - Bioenergetics
Issue number2
Publication statusPublished - Sep 10 1987



  • (A. nidulans)
  • Absorption spectroscopy
  • Antenna complex
  • Photosynthesis
  • Phycobilisome
  • Resonance Raman spectroscopy

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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