title: Ultrafast photoreaction dynamics of a light-driven sodium-ion-pumping retinal protein from Krokinobacter eikastus revealed by femtosecond time-resolved absorption spectroscopy.
abstract: We report the first femtosecond time-resolved absorption study on ultrafast photoreaction dynamics of a recently discovered retinal protein, KR2, which functions as a light-driven sodium-ion pump. The obtained data show that the excited-state absorption around 460 nm and the stimulated emission around 720 nm decay concomitantly with a time constant of 180 fs. This demonstrates that the deactivation of the S1 state of KR2, which involves isomerization of the retinal chromophore, takes place three times faster than that of bacteriorhodopsin. In accordance with this rapid electronic relaxation, the photoproduct band assignable to the J intermediate grows up at ∼620 nm, indicating that the J intermediate is directly formed with the S1 → S0 internal conversion. The photoproduct band subsequently exhibits a ∼30 nm blue shift with a 500 fs time constant, corresponding to the conversion to the K intermediate. On the basis of the femtosecond absorption data obtained, we discuss the mechanism for the rapid photoreaction of KR2 and its relevance to the unique function of the sodium-ion pump.
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.|Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology , Yokohama 226-8501, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Tahara
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takeuchi
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Rei
authors.initials: R
authors.lastname: Abe-Yoshizumi
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.|OptoBioTechnology Research Center, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.|PRESTO, Japan Science and Technology Agency , 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology , Yokohama 226-8501, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohtani
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.|OptoBioTechnology Research Center, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Tahei
authors.initials: T
authors.lastname: Tahara
keywords: all-trans retinal; cation pump; photoisomerization; photoreceptor protein; rhodopsin; ultrafast spectroscopy