Detection of N-acetylated forms of β-endorphin and nonacetylated α-MSH in the intermediate pituitary of the toad, Bufo marinus

Steady-state analysis of the acid extracts of the intermediate pituitary of the toad, Bufo marinus, revealed the presence of multiple forms of β-endorphin and α-MSH. Approximately 98% of the immunoreactive β-endorphin was N-acetylated. The major form of N-acetylated β-endorphin, which represented 81.5% of the total β-endorphin recovered from this tissue, had an apparent molecular weight of 1.2 kDa and a net charge of + 1 at pH 2.75. Approximately 98% of the immunoreactive α-MSH present in the Bufo intermediate pituitary had reverse phase HPLC properties similar to the nonacetylated form of α-MSH, ACTH(1–13)amide. These observations are in agreement with studies on the intermediate pituitary of the frog, Xenopus laevis, which have shown that the N-acetylation of α-MSH in this species is a cosecretory processing event, whereas the N-acetylation of β-endorphin is a posttranslational processing event (2, 5, 15). These observations indicate that the N-acetylation of β-endorphin and α-MSH occurs at distinct subcellular sites in intermediate pituitary cells of anuran amphibians. The Bufo intermediate pituitary will serve as a good model system for studying these novel N-acetyltransferase reactions.