Chemical and immunological characterization of salmon endorphins

Five new peptides related to salmon N-acetyl endorphin II (N-Ac-EP II) were isolated from an acid acetone extract of the pituitary. They were identified as EP II and four N-terminal fragments of N-Ac-EP II, namely N-Ac-EP II (1-18), (1-19), (1-20), and (1-29). The sequence comparison with mammalian EPs revealed that N-Ac-EP II (1-18) and (1-19) corresponded to mammalian alpha- and gamma-EP, respectively. The occurrence of peptides similar to mammalian alpha-, beta-, and gamma-EP indicates that further processing of EP takes place in both the teleost and mammalian pituitaries by similar pathways. A radioimmunoassay for salmon EPs has been developed with rabbit antiserum raised against salmon N-Ac-EP II. It was demonstrated that the antiserum showed full cross-reactivity with salmon N-Ac-EP I, N-Ac-EP II (1-20), and N-Ac-EP II (1-18), but none with Met-enkephalin, human beta-EP, and human beta-LPH. Similarly, the salmon EPs did not cross-react with human beta-EP antiserum in the radioimmunoassay.