Differences in the photobleaching process between 7-cis- and 11-cis-rhodopsins: a unique interaction change between the chromophore and the protein during the lumi-meta I transition.
The photochemical and subsequent thermal reactions of 7-cis-rhodopsin prepared from cattle opsin and 7-cis-retinal were investigated by low-temperature spectrophotometry and laser photolysis, and compared with those of 11-cis-rhodopsin prepared from cattle opsin and 11-cis-retinal. Low-temperature experiments revealed that the absorption maxima of batho and lumi intermediates from 7-cis-rhodopsin were at slightly shorter wavelengths than those of 11-cis-rhodopsin while the meta I intermediates of both rhodopsin isomers showed the same absorption maxima. Kinetic experiments of the photobleaching process of 7-cis-rhodopsin using picosecond and nanosecond laser pulses revealed the formation of intermediates corresponding to the batho, lumi, meta I, and meta II intermediates from 11-cis-rhodopsin. An intermediate of 7-cis-rhodopsin corresponding to photorhodopsin (a precursor of bathorhodopsin), however, was not detected. Batho and lumi intermediates from 7-cis-rhodopsin had shorter lifetimes (approximately 40 ns and 300 microseconds) than those of 11-cis-rhodopsin (250 ns and 800 microseconds), but the lifetime of the meta I intermediate from 7-cis-rhodopsin was identical with that from 11-cis-rhodopsin (12 ms). These results indicate that the difference in configuration of the original chromophore between 7-cis- and 11-cis-rhodopsins is a cause of different chromophore-opsin interactions in the batho and lumi stages, while in the meta I stage the difference has disappeared by the relaxation of the protein near the chromophores. A possible interaction change between the 9-methyl group of the chromophore and its neighboring protein during the lumi-meta I transition will be discussed.
Shichida
Y
Y
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Kandori
H
H
Okada
T
T
Yoshizawa
T
T
Nakashima
N
N
Yoshihara
K
K
D000818:Animals; D002417:Cattle; D005136:Eye Proteins / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D010777:Photochemistry; D012172:Retinaldehyde / Q000378:metabolism; D012243:Rhodopsin / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism; D017299:Rod Opsins; D013053:Spectrophotometry / Q000379:methods; D013997:Time Factors
D005136:Eye Proteins; D017299:Rod Opsins; D012243:Rhodopsin; D012172:Retinaldehyde