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 NH2-terminal sequences of adrenocorticotropin was studied by incubation of ACTH-(1-16)-NH2 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)-NH2 were isolated and characterized by their amino acid composition and NH2-terminal groups. Both at pH 7.4 and pH 8.5 the following fragments were found: ACTH-(3-16)-NH2, ACTH-(4-16)-NH2, ACTH-(5-16)-NH2, and ACTH-(7-16)-NH2. At pH 7.4 the major products were ACTH-(4-16)-NH2 and ACTH-(7-16)-NH2, while the peptide ACTH-(3-16)-NH2 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 NH2-terminus of adreno-corticotropin and related peptides by brain synaptic membranes.