Acetylation of αMSH and β-endorphin by rat neurointermediate pituitary secretory granule-associated acetyltransferase

ACTH(1-8) and ACTH(9-13)NH₂ were used as potential enzyme inhibitors to begin examining the relationship between the acetylation of ACTH- and β-endorphin-related peptides. ACTH(1-8) was a potent inhibitor of the acetylation of both ACTH- and β-endorphin-related peptides, whereas ACTH(9-13)NH₂ was an effective inhibitor only of the acetylation of ACTH-related substrates. This inhibition pattern indicated that there may be an unusual interaction between some ACTH- and β-endorphin-related peptides as substrates for the acetyltransferase. Utilizing HPLC to separate ACTH- and β-endorphin-related peptides present in the same reaction mixture, ACTH(1-14) and β-endorphin(1-27) at K_m and saturating concentrations were used as substrates to examine the ability of one peptide substrate to affect the acetylation of the other. It was observed that the acetylation of ACTH(1-14), even at K_m concentration, was relatively unaffected by the presence of β-endorphin(1-27). However, the acetylation of β-endorphin(1-27) was significantly reduced by the presence of ACTH(1-14). This preferential acetylation of ACTH-related peptides over the acetylation of β-endorphin-related peptides might have physiological importance under some conditions.