Generation of 1-37 and 1-38 forms of adrenocorticotropin by mono- and dipeptidyl serine carboxypeptidase activities in bovine pituitary secretory vesicles.
ACTH is a 39-amino acid peptide synthesized in the pituitary as part of the precursor molecule, POMC. Analysis of bovine anterior pituitary homogenates and secretory vesicles revealed that in addition to ACTH-(1-39), ACTH-(1-37) and ACTH-(1-38) were also present in the lobe, indicating that carboxyl-terminal processing of ACTH-(1-39) occurred in vivo. Mono- and dipe;tidyl carboxypeptidase activities that cleaved ACTH-(1-39) were detected in bovine intermediate and anterior pituitary secretory vesicle membranes and characterized. The dipeptidyl carboxypeptidase activity liberated ACTH-(1-37) and the dipeptide, Glu-Phe, and the monocarboxypeptidase activity generated, to a smaller extent, ACTH-(1-38) and phenylalanine from ACTH-(1-39). Kinetic studies indicated that the formation of ACTH-(1-37) occurred within minutes, whereas the formation of ACTH-(1-38) occurred within hours. Both enzymatic activities had a pH optimum of 5.5 and a Km of 14-18 microM for ACTH-(1-39), and were inhibited by serine and some thiol, but not metallo- or aspartic protease inhibitors. These unique serine carboxypeptidase(s) may function as a converting enzyme in vivo.
Friedman
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TC
Section of Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Chen
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HC
Loh
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YP
D000324:Adrenocorticotropic Hormone / Q000096:biosynthesis* / Q000378:metabolism; D000818:Animals; D002268:Carboxypeptidases / Q000378:metabolism*; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000378:metabolism*; D004798:Enzymes / Q000378:metabolism; D007700:Kinetics; D010446:Peptide Fragments / Q000096:biosynthesis*; D010902:Pituitary Gland / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011863:Radioimmunoassay
C027550:ACTH (1-38); D004798:Enzymes; D010446:Peptide Fragments; D011480:Protease Inhibitors; C042876:ACTH (1-37); D000324:Adrenocorticotropic Hormone; D002268:Carboxypeptidases; D010450:Endopeptidases; C020071:dipeptidyl carboxypeptidase; C022633:serine carboxypeptidase