Bioorganic studies with rhodopsin

An introductory review of visual transduction is followed by an account of external point charge models which were proposed to explain the red—shifted maxima in visual pigments and bacteriorhodopsin. 13—Ethylretinal, 13—propylretinal, and a retinal analog with an 8—membered ring in the side—chain yield bovine rhodopsin analogs which are bleachable but spontaneously regrow. This is a phenomenon not seen before in vitro in rhodopsins. The photoreceptor of the phototactic green algae Chlamydomonas has been found to be closely related to bovine rhodopsin but unlike bacteriorhodopsin; incubation of Chlamydomonas with retinal analogs shifts the phototaxis action spectral maxima in a manner similar to the shifts encountered in the bovine visual pigment. This is the first behavioral shift induced by analogs in a eukaryote. The studies also suggest that Chlamydomonas provides a convenient system for photoreceptor studies because of the availability of mutant strains, relative ease of experiment, and the short time needed to get results on minuscule amounts of analogs.