FORMATION OF 7-CIS-RETINAL AND 13-CIS-RETINAL PIGMENTS BY IRRADIATING SQUID RHODOPSIN

Squid rhodopsin was irradiated with orange light (>530 nm) at various temperatures from -190 to 10 °C until a photo-steady-state mixture was formed. Then the chromophoric retinals were extracted from the photo-steady-state mixtures and their isomer composition was analyzed by high-performance liquid chromatography. In the case of a photo-steady-state mixture formed at -85 °C, large peaks in the chromatogram were found at the positions of both 1-cis-and 13-cw-retinals. Each peak was further identified by synthesizing the pigments from these retinals with cattle opsin or apobacteriorhodopsin. Both 7-cis- and 13-m-retinals were also extracted from a photo-steady-state mixture formed by irradiation at -40, at 0, or at 10 °C. These isomers were scarcely detected in a photo-steady-state mixture formed by irradiation at -190 °C, though 9-cis-retinal was found as a major constituent in this mixture. Irradiation of lumirhodopsin at -190 °C, however, produced 7-cis-retinal pigment. These findings suggest that bathorhodopsin may have a conformation to prevent the formation of 7-cis-retinal from the all-trans form and that this particular conformation may be relaxed by the conversion of bathorhodopsin to lumirhodopsin. © 1979, American Chemical Society. All rights reserved.