Fig. 6
Retinyl-lipid photoregeneration of opsins in rod or cone OS. The results presented here suggest the existence of a light-driven mechanism to regenerate visual pigments in rod and cone OS through photoisomerization of retinyl-lipids. This diagram shows the phospholipid bilayer of a rod OS disk. Rhodopsin absorbs a 500-nm photon (hv) that photoisomerizes its 11cRAL chromophore to atRAL, converting the pigment to its active metarhodopsin II/III (meta II/III) state. After a brief signaling period, the bleached opsin decays, releasing free atRAL into the bilayer. The atRAL reversibly condenses with PE (yellow circles) to form at-N-ret-PE. Protonated at-N-ret-PE is converted specifically to 11c-N-ret-PE upon absorption of a 450-nm photon. Spontaneous hydrolysis of 11c-N-ret-PE yields free 11cRAL, which irreversibly combines with unliganded apo-opsin to form a new rhodopsin pigment. A similar process occurs in cone OS to regenerate cone opsin pigments
