Identification of beta-endorphins in the pituitary gland and blood plasma of the common carp (Cyprinus carpio)

Carp P-endorphin is posttranslationally modified by N-terminal acetylation and C-terminal cleavage. These processes determine the biological activity of the P-endorphins. Forms of P-endorphin were identified in the pars inter media and the pars distalis of the pituitary gland of the common carp (Cypr inus carpio), as well as the forms released in vitro and into the blood. Af ter separation and quantitation by high performance liquid chromatography ( HPLC) coupled with radioimmunoassay, the beta -endorphin immunoreactive pro ducts were identified by electrospray ionisation mass spectrometry and pept ide sequencing. The release of beta -endorphins by the pituitary gland was studied after stimulation with corticotrophin-releasing factor (CRF) in vit ro. In the pars intermedia, eight N-acetylated truncated forms were identif ied. Full length N-acetyl beta -endorphin(1-33) correlated with N-acetyl be ta -endorphin(1-29) and these forms together ;mounted to over 50% of total immunoreactivity. These products were partially processed to N-acetyl beta -endorphin(1-15) (30.8% of total immunoreactivity) and N-acetyl beta -endor phin(1-10) (3.1%) via two different cleavage pathways. The acetylated carp homologues of mammalian alpha- and gamma -endorphin were also found. N-acet yl beta -endorphin(1-15) and (1-29) and/or (1-33) were the major products t o be released in vitro, and were the only acetylated beta -endorphins found in blood plasma, although never together. CRF stimulated the release of op ioid B-endorphin from the pars distalis. This non-acetylated P-endorphin re presents the full length peptide and is the most abundant form in plasma.