Action of peptidases in brain synaptic membranes on the NH2-terminus of adrenocorticotropin using ACTH-(1–16)-NH2 as a model substrate

The action of brain peptidases on NH 2 -terminal sequences of adrenocorticotropin was studied by incubation of ACTH-(1-16)-NH 2 under different pH conditions. Profiles of metabolites and time course of product formation were obtained by HPLC analysis of the digests. Fragments of ACTH-(1-16)-NH 2 were isolated and characterized by their amino acid composition and NH 2 -terminal groups. Both at pH 7.4 and pH 8.5 the following fragments were found: ACTH-(3–16)-NH 2 , ACTH-(4-16)-NH 2 , ACTH-(5–16)-NH 2 , and ACTH-(7–16)-NH 2 . At pH 7.4 the major products were ACTH-(4–16)-NH 2 and ACTH-(7–16)-NH 2 , while the peptide ACTH-(3-16)-NH 2 was the main metabolite at pH 8.5. The nature of identified peptides and the time course of their formation demonstrates that aminopeptidase activities predominate in the conversion of the NH 2 -terminus of adrenocorticotropin and related peptides by brain synaptic membranes.