DIFFERENTIAL N-ACETYLATION OF ALPHA-MSH AND BETA-ENDORPHIN IN THE INTERMEDIATE PITUITARY OF THE TURTLE, PSEUDEMYS-SCRIPTA

Steady-state analyses of the intermediate pituitary of the turtle, Pse udemys scripta, indicated that alpha-MSH-sized immunoreactive forms an d beta-endorphin-sized immunoreactive forms are major end products of melanotropic cells. Three forms of alpha-MSH-related immunoreactivity were detected. The two major forms had the same reversed-phase HPLC pr operties as synthetic N,O-diacetyl-ACTH(1 - 13)-NH2 and N-acetyl-ACTH( 1 - 13)-NH2. These forms accounted for 97% of the total alpha-MSH-rela ted immunoreactivity detected. A minor peak of ACTH(1 - 13)-NH2 was al so detected. Multiple forms of beta-endorphin-related immunoreactivity were detected, which varied in net positive charge (+1 to +5), appare nt molecular weight (2.4 to 3.5 kDa), and degree of N-terminal acetyla tion. Although N-acetylated forms of beta-endorphin were detected in t he turtle intermediate pituitary, the major forms of turtle beta-endor phin were nonacetylated. These features of the turtle intermediate pit uitary POMC-specific N-acetylation mechanism are similar to, yet disti nct from, the POMC N-acetylation mechanisms observed for mammals. Thes e data suggest that POMC-specific N-acetylation mechanisms were presen t in reptiles prior to the divergence of the anapsid and synapsid line s.