The nucleotide sequence of the human gene for proopiomelanocortin (POMC) was characterized in 1980. The POMC gene codes for endogenous opioids such as β-endorphin and gamma-endorphin. The peptides with opioid activity that are derived from proopiomelanocortin comprise the class of endogenous opioid peptides called "endorphins".
The human gene for enkephalins was isolated and its sequence described in 1982.
The human gene for dynorphins (originally called the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983.
The PNOC gene encoding prepronociceptin, which is cleaved into nociceptin and potentially two additional neuropeptides.
^Noda M, Teranishi Y, Takahashi H, Toyosato M, Notake M, Nakanishi S, Numa S (June 1982). "Isolation and structural organization of the human preproenkephalin gene." Nature". 1982 Jun 3;' 297 (5865): 431–4. doi:10.1038/297431a0. PMID6281660.
^Horikawa S, Takai T, Toyosato M, Takahashi H, Noda M, Kakidani H et al. (Dec 1983). "Isolation and structural organization of the human preproenkephalin B gene". Nature306 (5943): 611–4. doi:10.1038/306611a0. PMID6316163.