title: Structure and interactions of phycocyanobilin chromophores in phycocyanin and allophycocyanin from an analysis of their resonance raman spectra.
abstract: Raman spectra of phycocyanobilin, phycocyanin, and allophycocyanin were obtained at resonance with their visible and near-UV transitions. These spectra were empirically assigned with the help of 14N- and 15N-isotopic substitutions and comparisons with resonance Raman spectra of phycoerythrin. These results confirm the previously suggested assignment of a conformation-sensitive band around 1239-1246 cm-1 to a mode involving nu CmH and nu CN coordinates. Computer-assisted decomposition of the complex, conformation-sensitive 1580-1670-cm-1 region yielded five components that we labeled I-V. The previously described spectral changes observed upon monomerization and denaturation in resonance Raman spectra of phycocyanin and allophycocyanin essentially arise from changes in the relative intensities of these components. Component I (around 1649-1651 cm-1) and component III (1621-1624 cm-1) originate predominantly from nu C=C at C15 of the chromophore. Their relative intensity ratio reflects the relative amounts of C15-Z-anti and C15-Z-syn methine bridge conformations, respectively. Component II (1633-1638 cm-1) is ascribed to a nu C=C mode of pyrrole rings; it is not sensitive to the chromophore conformation. Component IV is also conformation-insensitive and originates from nu C=N and nu C=C coordinates, most likely from ring C. Component V (1591-1594 cm-1) involves a nu C=N coordinate in ring D, coupled to a nu C=C coordinate of the C15 methine bridge. The implications of the present assignments on those of resonance Raman active modes of phytochrome are discussed. A consistent set of correlations between chromophore conformations and resonance Raman data is obtained for both phycobiliproteins and phytochrome.
authors.affiliation: Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, Szeged.
authors.forename: B
authors.initials: B
authors.lastname: Szalontai
authors.forename: Z
authors.initials: Z
authors.lastname: Gombos
authors.forename: V
authors.initials: V
authors.lastname: Csizmadia
authors.forename: C
authors.initials: C
authors.lastname: Bagyinka
authors.forename: M
authors.initials: M
authors.lastname: Lutz
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry; D008027:Light; D008432:Mathematical Computing; D008968:Molecular Conformation; D009587:Nitrogen Isotopes; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry* / Q000528:radiation effects; D010799:Phycoerythrin / Q000737:chemistry / Q000528:radiation effects; D011489:Protein Denaturation; D011758:Pyrroles / Q000737:chemistry* / Q000528:radiation effects; D013059:Spectrum Analysis, Raman; D045725:Tetrapyrroles; D014466:Ultraviolet Rays
chemical_list: D009587:Nitrogen Isotopes; D052980:Phycobilins; D011758:Pyrroles; D045725:Tetrapyrroles; C002497:allophycocyanin; D010798:Phycocyanin; D010799:Phycoerythrin; C011069:phycocyanobilin