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Photoisomerization in rhodopsin
H Kandori1, Y Shichida, T Yoshizawa
1Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan. kandori@photo2.biophys.kyoto-u.ac.jp
Biochemistry. Biokhimiia
|December 18, 2001
Summary
Rhodopsin
Area of Science:
- Biochemistry
- Photochemistry
- Molecular Biology
Background:
- Rhodopsin, a key pigment in twilight vision, utilizes 11-cis retinal as its chromophore.
- The chromophore is linked to a lysine residue via a protonated Schiff base.
- Photon absorption triggers the primary photochemical reaction within the chromophore.
Purpose of the Study:
- To review primary reaction processes in rhodopsin.
- To elucidate the role of the protein environment in chromophore photoisomerization.
- To understand the mechanism of light-induced signal transduction in vision.
Main Methods:
- Picosecond and femtosecond time-resolved spectroscopy (transient absorption and fluorescence).
- Infrared spectroscopy at low temperatures.
- Analysis of crystal structures of rhodopsin and its analogs.
Main Results:
- Cis-trans isomerization of 11-cis retinal is the primary photochemical reaction.
- Photoisomerization in rhodopsin is a vibrationally coherent process, occurring within 200 femtoseconds.
- The protein environment significantly facilitates faster chromophore isomerization compared to solution.
- Protein residue contributions to the reaction mechanism were monitored.
Conclusions:
- The protein environment plays a crucial role in accelerating the photoisomerization of the rhodopsin chromophore.
- Femtosecond spectroscopy provides real-time insights into the coherent nature of this photochemical process.
- Advances in structural biology, like the bovine rhodopsin crystal structure, will enhance mechanistic understanding.