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Synthesis of a Photoaffinity‐Labeled (11 Z )‐Retinal: Identification of Retinal/Rhodopsin Cross‐Linked Sites along the Visual‐Transduction Path
Author(s) -
Souto Maria L.,
Um Joann,
Borhan Babak,
Nakanishi Koji
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20000906)83:9<2617::aid-hlca2617>3.0.co;2-9
Subject(s) - chemistry , rhodopsin , retinal , stereochemistry , visual phototransduction , photoaffinity labeling , opsin , chromophore , ring (chemistry) , photochemistry , biochemistry , binding site , organic chemistry
The retinal chromophore (11 Z )‐3‐diazo‐4‐oxoretinal ( 1 ) with two photo‐labile moieties has been synthesized by semi‐hydrogenation of an 11‐yne precursor with activated Zn in aqueous media. Incorporation of 1 into opsin yielded diazoketo rhodopsin (DK‐Rh), which, upon bleaching, gave rise to intermediates batho‐Rh, lumi‐Rh, meta‐Rh, and meta‐II‐Rh corresponding to those of native Rh but at lower temperatures. Photoaffinity labeling of DK‐Rh and these bleaching intermediates showed that the ionone ring cross‐linked to Trp265 of helix F in DK‐Rh and batho intermediate, and to Ala169 of helix D in lumi, meta‐I, and meta‐II intermediates. These results demonstrate the occurrence of large conformational changes along the visual transduction path, which, in turn, is responsible for activation of the G‐protein.