Definitions for opsinˈɒp sɪn
Random House Webster's College Dictionary
any of several compounds that form the protein component of the light-sensitive pigment rhodopsin.
Origin of opsin:
1950–55; prob. back formation from rhodopsin
retinal protein formed by the action of light on rhodopsin
Any of a group of light-sensitive proteins in the retina
Opsins are a group of light-sensitive 35–55 kDa membrane-bound G protein-coupled receptors of the retinylidene protein family found in photoreceptor cells of the retina. Five classical groups of opsins are involved in vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the visual transduction cascade. Another opsin found in the mammalian retina, melanopsin, is involved in circadian rhythms and pupillary reflex but not in image-forming.