Anti-proenkephalin antibodies are used in the immunodetection of the protein encoded by the PENK gene. In humans, the canonical protein has a reported length of 267 amino acid residues and a mass of 30.8 kDa. Its subcellular localization is in the cytoplasmic vesicles and is also secreted. A member of the Opioid neuropeptide precursor protein family, it is reported to be a neuropeptide that competes with and mimic the effects of opiate drugs. Post-translational modifications have been described, including protein cleavage. Other names for this target antigen include PENK-A, proenkephalin-A, enkephalin A, peptide F, preproenkephalin, and PE.