The function of OPRPN (opiorphin prepropeptide, ENSG00000171199) is as follows. Opiorphin is an endogenous inhibitor of neprilysin and aminopeptidase N. Inhibits the breakdown of substance P, Mca-BK2 and Met-enkephalin by neprilysin in vitro with IC(50) values of 29 uM, 33 uM and 33 uM respectively. Inhibits the breakdown of Ala-pNA by aminopeptidase N in vitro with an IC(50) of 65 uM. Has a potent analgesic effect when administered to rats by intravenous injection. .