Anti-R21 antibodies are readily available from several suppliers. R21 is a reported synonym of the human protein 'opioid receptor kappa 1', encoded by the gene OPRK1. The full protein is reported to be 380 amino acid residues in length. It is listed to be a member of the G-protein coupled receptor 1 family. Consult the antibody supplier page for essential details, including target immunogenicity and tested applications.