all-trans-retinal

All-trans-retinal (Vitamin A aldehyde) is a one of the major vitamin A metabolites in the retina. All-trans-RAL is regenerated to the visual chromophore, 11-cis-retinal in physiological conditions.

11-cis Retinal is a chromophore that binds to opsin in the mammalian visual system as an inverse agonist forming the inactive conformation of rhodopsin. When 11-cis retinal absorbs a photon of light, it isomerizes to form all-trans retinal beginning the phototransduction cycle, which is the basis for mammalian vision. A G121L mutation in opsin allows 11-cis retinal to bind as a partial agonist and activate rhodopsin in the absence of light. In a moth model of carotenoid deficiency-induced low visual sensitivity, 11-cis retinal application to compound eyes restored visual sensitivity almost completely.