title: Assignment of the vibrational modes of the chromophores of iodopsin and bathoiodopsin: low-temperature fourier transform infrared spectroscopy of 13C- and 2H-labeled iodopsins.
abstract: To investigate the chromophore structures of iodopsin and its low-temperature photoproducts, we have assigned their vibrational bands in the Fourier transform infrared (FTIR) spectra using iodopsin samples that were reconstituted with a series of (13)C- and deuterium-labeled retinals. The analyses of the vibrational bands in the fingerprint and hydrogen-out-of-plane (HOOP) regions indicated that the structure of the chromophores in the iodopsin system differs near their centers from those in the rhodopsin system. Compared to rhodopsin, the chromophore of the batho intermediate of iodopsin is twisted in the C(12) to C(14) regions but is more planar around C(11) region. The large amount of twisting was reduced by removing the chloride ion from the iodopsin, suggesting that this twisting hinders the relaxation of the torsion near C(11) necessary for the transition to the lumi intermediate and thus results in the thermal reversion of the batho intermediate back to the iodopsin. From the analyses of the C=NH and C=ND stretching bands, we conclude that the displacement of the Schiff base region upon photoisomerization of the chromophore is restricted, as is the case for rhodopsin. These results indicated that iodopsin's chromophore has a unique structure near its center and that this difference is enhanced by the binding of chloride nearby.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hirano
authors.forename: Naoko
authors.initials: N
authors.lastname: Fujioka
authors.forename: Hiroo
authors.initials: H
authors.lastname: Imai
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.forename: Akimori
authors.initials: A
authors.lastname: Wada
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Ito
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shichida
mesh_terms: D002712:Chlorides; D012168:Retinal Pigments / Q000737:chemistry*; D012243:Rhodopsin; D017299:Rod Opsins / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013696:Temperature
chemical_list: D002712:Chlorides; D012168:Retinal Pigments; D017299:Rod Opsins; D012545:Schiff Bases; C034941:iodopsin; D012243:Rhodopsin