Ready-to-use ELISA kits are available for the detection of opsin 4 (melanopsin), an alias of the protein, opsin 4. The official gene symbol is OPN4. The kits can detect several species variants of the protein, including: mouse. The protein, with a mass of 52.6 kDa and length of 478 residues, is reported to be membrane-associated. It is a member of the G-protein coupled receptor 1 family, Opsin subfamily and may be known by other names, including: MOP, and melanopsin.