The 3, 4‐didehydroretinal chromophore of goldfish porphyropsin

Abstract

The isomeric configuration of the 3,4‐didehydroretinal chromophore of goldfish porphyropsin was determined by high performance liquid chromatography (HPLC) and by the regeneration of this visual pigment with authentic isomers of 3,4‐didehydroretinal. A nonisomerizing, quantitative method using hydroxylamine and methylene chloride was employed to extract the 3,4‐didehyroretinal chromophore from the rod outer segment membrane (containing the porphyropsin). When this extracted chromophore was injected into the HPLC, only a single major peak was observed and this peak coeluted with the authentic 11‐cis 3,4‐didehydroretinyl oxime. This suggests that the chromophore of goldfish porphyropsin is 11‐cis 3,4‐didehydroretinal. When the bleached rod outer segments (containing the opsin) were incubated with different 3,4‐didehydroretinal isomers (13‐cis, 11‐cis, 9‐cis, and all‐trans), only the 11‐cis isomer resulted in the degeneration of porphyropsin. This also suggests that the porphyropsin chromophore exists in the 11‐cis configuration.