title: Purification and partial characterization of a heat-resistant, cytosolic neuropeptidase from rat liver.
abstract: A cholecystokinin octapeptide (CCK-8)-degrading peptidase was purified from rat liver cytosol by heat precipitation of other proteins followed by gel filtration, ion exchange chromatography and preparative gel electrophoresis, using a silicate binding assay to quantitate the degradation of radiolabeled CCK-8. The purified peptidase (M(r) approximately 60,000) had a pH optimum of 6.0; its activity was inhibited by EDTA and 1, 10-phenanthroline but not by phosphoramidon, calpain inhibitor I, bestatin or bacitracin. CCK-8 peptidase rapidly degraded radiolabeled Met-enkephalin as well as 125I-CCK-8, but not a series of other unrelated peptides. Unlabeled Leu-enkephalin, beta-casomorphin and neurotensin competitively inhibited the degradation of 125I-CCK-8, suggesting that these opioids are also substrates for the enzyme. These data suggest that this protein is a novel hepatic enzyme which may play a role in the degradation of neuropeptides.
authors.affiliation: Center for Basic Research in Digestive Diseases, Mayo Medical School, Rochester, MN 55905.
authors.forename: R M
authors.initials: RM
authors.lastname: Janas
authors.forename: D L
authors.initials: DL
authors.lastname: Marks
authors.forename: N F
authors.initials: NF
authors.lastname: LaRusso
mesh_terms: D000818:Animals; D003600:Cytosol / Q000201:enzymology*; D004492:Edetic Acid / Q000494:pharmacology; D010450:Endopeptidases / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000201:enzymology*; D010618:Phenanthrolines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012844:Sincalide / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D010618:Phenanthrolines; D011480:Protease Inhibitors; D004492:Edetic Acid; D010450:Endopeptidases; D012844:Sincalide; C025205:1,10-phenanthroline