title: Identification of retinal isomers isolated from bacteriorhodopsin.
abstract: The purple membrane of Halobacterium halobium contains the protein bacteriorhodopsin which resembles the visual pigment, rhodopsin, in many aspects. The isomeric configurations of its chromophore, retinal, were studied by a combination of methylene chloride extraction and analysis by high-pressure liquid chromatography. The light-adapted form bR570LA yields solely all-trans-retinal, while the dark-adapted form of bacteriorhodopsin, bR560DA, yields a mixture of 13-cis and all-trans with a ratio of similar to 1;1. The photointermediate M412 in a membrane modified by ether at high NaCl concentration also yields an approximately 1:1 mixture of 13-cis-and all-trans-retinals, while a similar M405 species produced by illumination in 2 M guanidine hydrochloride at high pH yields mainly 13-cis-retinal. These results indicate that the photochemical cycle of bR570LA may involve an isomerization of the retinal chromophore from the all-trans to the 13-cis form.
mesh_terms: D001436:Bacteriorhodopsins; D002338:Carotenoids; D003623:Dark Adaptation; D006217:Halobacterium; D008027:Light; D012172:Retinaldehyde / Q000032:analysis*; D013237:Stereoisomerism; D014801:Vitamin A / Q000031:analogs & derivatives*
chemical_list: D014801:Vitamin A; D002338:Carotenoids; D001436:Bacteriorhodopsins; D012172:Retinaldehyde