Breakdown of corticotropin-(1-24) by mouse brain extracts.

ACTH-(1–24) was rapidly degraded to its constituent amino acids upon incubation with soluble mouse brain preparations. Breakdown had a pH optimum near neutrality, a K_m of 1 × 10^?4m, and a V_max of 63 nmol/mg protein/h. Initially a preferential liberation of the amino acids of the N-terminal region of the hormone was observed, followed shortly by a relatively uniform release of amino acids originating throughout the ACTH-(1–24) sequence. Enzymes cleaving internal bonds appear to play a major role in the degradation. The short lag period between hormone disappearance and amino acid formation indicated that few if any large peptides were accumulated during incubation. Pepstatin, chymostatin, antipain, leupeptin, bacitracin, l-1-tosylamide-2-phenylethylchloromethyl ketone, soybean trypsin inhibitor, and diisopropyl-fluorophosphate had little or no effect on amino acid release. Puromycin, bestatin, and EDTA partially inhibited amino acid formation, affecting mainly the residues in the central and carboxyl portions of ACTH-(1–24). N-Ethylmaleimide strongly inhibited the release of all amino acids, indicating extensive involvement of sulfhydryl peptidases in ACTH-(1–24) breakdown.