Visual pigments are the light-absorbing molecules that mediate vision. They consist of an apoprotein, opsin, covalently linked to cis-retinal. Retina. Expressed in the hyperpolarizing cell layer of the photoreceptor cells with its photoreceptive region adjacent to the lens. Phosphorylated on some or all of the serine and threonine residues present in the C-terminal region. Belongs to the G-protein coupled receptor 1 family. Opsin subfamily.