5 NON-BLEACHABLE RHODOPSINS RETAINING THE FULL NATURAL CHROMOPHORE
Details
The crucial primary step in visual transduction is known to be the 11-cis to trans isomerization of the rhodopsin chromophore, which is the protonated Schiff base of 11-cis retinal. Four retinoids 1-4 in which the 11-ene bond is locked into 11-cis geometry by virtue of their cycloheptatrienylidene moieties have been synthesized; these four molecules correspond to 11-cis, 11,13-dicis, 9,11-dicis, and 9,11,13-tricis retinals. All four have been found to bind to cattle opsin to form the corresponding rhodopsin analogs. These pigments, while retaining the full chromophore, are nonbleachable when exposed to light corresponding to their absorption maxima. These studies show that retinals locked into the 11-cis geometry by 7-membered rings undergo no photoisomerization and block the bleaching of visual pigments; namely an 11-cis to trans isomerization is a prerequisite for visual transduction.
