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CONFORMATIONAL ANALYSIS OF THE RHODOPSIN CHROMOPHORE USING BICYCLIC RETINAL ANALOGUES
Author(s) -
Ito Masayoshi,
Katsuta Yuko,
Imamoto Yasushi,
Shichida Yoshinori,
Yoshizawa Tôru
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb09713.x
Subject(s) - rhodopsin , chromophore , chemistry , circular dichroism , retinaldehyde , stereochemistry , retinal , moiety , bicyclic molecule , enantiomer , opsin , crystallography , photochemistry , biochemistry
— For investigation of the chromophore conformation around the trimethyl cyclohexene ring and of the origin of the induced β‐circular dichroism band in rhodopsin, two C 6 ‐C 7 single bond‐fixed retinal analogues, 6s‐cb‐ and 6s‐trans‐locked bicyclic retinals (6 and 7, respectively) were synthesized and incorporated into bovine opsin in CHAPS‐PC mixture. 6s‐cb‐ and 6s‐tram‐Locked rhodopsin analogues (8 and 9 ) with A max at 539 and 545 nm, respectively, were formed. Interestingly, both 8 and 9 displayed α‐ and β‐circular dichroism bands. The ellipticity of α‐bands are similar in each other, while the β‐band of 8 was about three times stronger than that of 9. Irradiation of 6s‐trans‐locked rhodopsin, 9, in the presence of hyroxylamine, resulted in the formation of only one of the enantiomers of 6s‐rrans‐locked retinal oxime showing a positive circular dichroism signal at around 390 nm. This fact strongly suggests that the retinal binding site of rhodopsin shows a chiral discrimination. From these experimental results, the interactions between the trimethyl cyclohexene ring portion in the chromophore and the neighbouring protein moiety in the rhodopsin molecule are discussed.