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FTIR study of the photoinduced processes of plant phytochrome phyA using isotope-labeled bilins and density functional theory calculations
Citation key ISI:000257719200027
Author Schwinté, Pascale and Foerstendorf, Harald and Hussain, Zakir and G�rtner, Wolfgang and Mroginski, Maria-Andrea and Hildebrandt, Peter and Siebert, Friedrich
Pages 1256-1267
Year 2008
ISSN 0006-3495
DOI 10.1529/biophysj.108.131441
Address 9650 ROCKVILLE PIKE, BETHESDA, MD 20814-3998 USA
Journal Biophys. J.
Volume 95
Number 3
Month AUG 1
Abstract Fourier transform infrared spectroscopy was used to analyze the chromophore structure in the parent states Pr and Pfr of plant phytochrome phyA and the respective photoproducts lumi-R and lumi-F. The spectra were obtained from phyA adducts assembled with either uniformly or selectively isotope-labeled phytochromobilin and phycocyanobilin. The interpretation of the experimental spectra is based on the spectra of chromophore models calculated by density functional theory. Global C-13-labeling of the tetrapyrrole allows for the discrimination between chromophore and protein bands in the Fourier transform infrared difference spectra. All infrared difference spectra display a prominent difference band attributable to a stretching mode with large contributions from the methine bridge between the inner pyrrole rings (B-C stretching). Due to mode coupling, frequencies and isotopic shifts of this mode suggest that the Pr chromophore may adopt a distorted ZZZssa or ZZZasa geometry with a twisted A-B methine bridge. The transition to lumi-R is associated with only minor changes of the amide I bands indicating limited protein structural changes during the isomerization site of the C-D methine bridge. Major protein structural changes occur upon the transition to Pfr in which the chromophore adopts a ZZEssa or ZZEasa-like state. In addition, specific interactions with the protein alter the structure of the B-C methine bridge as concluded from the substantial downshift of the respective stretching mode. These interactions are removed during the photoreaction to lumi-F (ZZE -> ZZZ), which involves only small protein structural changes.
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