Photochemistry of the retinal chromophore in the process of seeing (vision)

The process of vision is a complex biochemical process that involves the participation of two types of retinal photoreceptor cells: rod cells and cone cells. These visual pigments possess the chromophore, 11-cis-retinal, linked through a Schiff base linkage to the opsin protein. Absorption of light by the visual pigment leads to the photoexcitation followed by photoisomerization, 11-cis-retinal (Z) to all-trans-retinal (E) for the activation of transducin, a heterotrimeric G-protein, to generate a nerve signal that is transmitted to the brain to produce the sense of vision. The photoisomerized pigment undergoes rapid hydrolysis to produce the opsin protein and all-trans-retinal that can be reconverted enzymatically to 11-cis-retinal for recharging the opsin protein to regenerate the active visual pigment to maintain the Wald’s visual cycle.