(3S)-11-cis-3-hydroxyretinal is one of three chromophores, which then associate with rhodopsins. Specifically, this chromophore associates with the Rh1 rhodopsin, a blue/green sensitive visual pigment found in 6 of the 8 photoreceptor cells in Drosophila melanogaster. The production of this chromophore begins with zeaxanthin obtained from Drosophila’s dietary sources. This lipid is broken down into (3R)-11-cis-3-hydroxyretinal and (3R)-all-trans-3-hydroxyretinal by a carotenoid isomerooxygenase. The (3R)-cis-3-hydroxyretinal is then attached to a retinoid binding protein, and this complex goes on to be used in the visual cycle of the organism. However, (3R)-all-trans-3-hydroxyretinal must be further processed. It too binds to a retinoid binding protein that will remain unchanged through the rest of the reactions. First, this complex will have a hydrogen added by a photoreceptor dehydrogenase in order to form (3R)-all-trans-3-hydroxyretinol, and then a photoreceptor epimerase will invert its stereochemistry to form (3S)-all-trans-3-hydroxyretinol. From here, an unknown protein, an oxidoreductase that transposes C=C bonds, will form (3S)-11-cis-3-hydroxyretinol. Finally, another photoreceptor dehydrogenase removes a hydrogen from that complex, forming the final product, (3S)-11-cis-3-hydroxyretinal. This complex then joins (3R)-11-cis-3-hydroxyretinal in the visual cycle.

11-cis-3-Hydroxyretinal Biosynthesis References