title: Thiol and aspartyl proteolytic activities in secretory vesicles of bovine pituitary.
abstract: Thiol and aspartyl proteolytic activities in isolated secretory vesicles of neural (NL) and intermediate (IL) lobes of bovine pituitary were characterized with heterologous enkephalin and tachykinin precursor substrates, 35S-(Met)-preproenkephalin and 35S-(Met)-beta-preprotachykinin. IL and NL secretory vesicles contained thiol-dependent proteolytic activity that cleaved the enkephalin precursor with a pH optimum of 4.5; this activity resembled a novel "prohormone thiol protease' previously purified and characterized from adrenal medulla chromaffin granules. IL and NL vesicles also demonstrated aspartyl proteolytic activity with acidic pH optimum, as shown by pepstatin A inhibition of tachykinin and enkephalin precursor cleaving activity. This activity may be related to a previously characterized chromaffin granule aspartyl protease (CGAP) related to cathepsin D (2), as indicated by the presence of immunoreactive CGAP in NL secretory vesicles by anti-CGAP immunoblots. These results show that pituitary secretory vesicles, like chromaffin granules, may contain similar thiol-dependent and aspartyl proteolytic activities.
authors.affiliation: Department of Biochemistry, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
authors.forename: C S
authors.initials: CS
authors.lastname: Toomim
authors.forename: V Y
authors.initials: VY
authors.lastname: Hook
mesh_terms: D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D002837:Chromaffin Granules / Q000201:enzymology; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000201:enzymology*; D004745:Enkephalins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D010902:Pituitary Gland / Q000201:enzymology* / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011498:Protein Precursors / Q000378:metabolism; D015320:Tachykinins / Q000378:metabolism
chemical_list: D004745:Enkephalins; D011480:Protease Inhibitors; D011498:Protein Precursors; D015320:Tachykinins; C044206:preprotachykinin; C033660:preproenkephalin; D003546:Cysteine Endopeptidases; D016282:Aspartic Acid Endopeptidases