title: Characterization of pro-opiocortin-converting activity in purified secretory granules from rat pituitary neurointermediate lobe.
abstract: Lysates of secretory granules from rat pituitary neurointermediate lobes were incubated with [3H]arginine- or [3H]phenylalanine-labeled toad pro-opiocortin. The processed products formed were identified by immunoprecipitation with adrenocorticotropin (ACTH) and endorphin antisera and by migration behavior on acid/urea/polyacrylamide gels. Pro-opiocortin was cleaved by the proteolytic activity in the secretory granule fraction to approximately 21,000 Mr ACTH, approximately 13,000 Mr ACTH, alpha-melanotropin, 16,000 Mr NH2-terminal glycopeptide, beta-lipotropin, and an endorphin-related peptide. Characterization of this pro-opiocortin-converting activity shows that it (i) is present in membrane and soluble fractions of the granule lysates, (ii) has a pH optimum of 5.0, (iii) appears to cleave at pairs of basic amino acid residues in the precursor, and (iv) is inhibited by leupeptin, pepstatin A, and p-chloromercuribenzoate but not diisopropyl fluorophosphate, N alpha-p-tosyl-L-lysine chloromethyl ketone hydrochloride, chloroquine, or EDTA. These inhibitor studies suggest that the converting-enzyme activity is due to an acid thiol, arginyl protease, distinct from any known cathepsin B-like activity.
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D003594:Cytoplasmic Granules / Q000201:enzymology*; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D009074:Melanocyte-Stimulating Hormones / Q000032:analysis; D010902:Pituitary Gland / Q000201:enzymology*; D010908:Pituitary Hormones, Anterior / Q000378:metabolism*; D011333:Pro-Opiomelanocortin; D043484:Proprotein Convertases; D011480:Protease Inhibitors / Q000494:pharmacology; D011498:Protein Precursors / Q000378:metabolism*; D051381:Rats
chemical_list: D010908:Pituitary Hormones, Anterior; D011480:Protease Inhibitors; D011498:Protein Precursors; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D009074:Melanocyte-Stimulating Hormones; D010450:Endopeptidases; D043484:Proprotein Convertases