Visual pigments such as rhodopsin and porphyropsin are light-absorbing molecules that mediate vision. Rhodopsin consists of an apoprotein, opsin, covalently linked to 11-cis-retinal. This receptor is coupled to the activation of phospholipase C. Porphyropsin consists of opsin covalently linked to 11-cis 3,4-didehydroretinal. Retina. Expressed in the depolarizing cell layer of the photoreceptor cells distant from 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.