Photoreceptor. Light-induced isomerization of 11-cis to all-trans retinal triggers a conformational change that activates signaling via G-proteins. Pineal gland. Instead of the rod where rhodopsin is generally located. Contains one covalently linked retinal chromophore. Upon light absorption, the covalently bound 11-cis-retinal is converted to all-trans-retinal. After hydrolysis of the Schiff base and release of the covalently bound all-trans-retinal, active rhodopsin is regenerated by binding of a fresh molecule of 11-cis-retinal. Belongs to the G-protein coupled receptor 1 family. Opsin subfamily.