title: Evidence of proteasome-mediated cytochrome P-450 degradation.
abstract: The cytochrome P-450 family of enzymes performs an incredibly diverse range of detoxification and oxidation reactions within the cell and constitutes between 5 and 10% of protein in hepatic endoplasmic reticulum. In this report it is demonstrated that constitutively expressed membranous P-450s are targeted for destruction by the proteasome, in a process which is ubiquitin-independent and is demonstrated in vitro to require prior labilization of the enzyme. This process was specific for P-450s CYP1A2, CYP2E1, CYP3A, and CYP4A and was not demonstrated to be involved in the turnover of CYP1A1, CYP2B1/2, or NADPH reductase. In reconstitution experiments using purified proteasomes and microsomal fractions, labilized P-450 conformations are protected from 20 S proteasome degradation by substrate addition, with proteolysis occurring while P-450s are still attached to the endoplasmic reticulum.
authors.affiliation: Laboratory of Clinical Studies, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892-1256, USA. roberts@clinpharm.niaaa.nih.gov
authors.forename: B J
authors.initials: BJ
authors.lastname: Roberts
mesh_terms: D000111:Acetylcysteine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D042926:Cytochrome P-450 CYP4A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007976:Leupeptins / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; C063261:acetylleucyl-leucyl-norleucinal; C067713:lactacystin; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; D019388:Cytochrome P-450 CYP1A2; D051544:Cytochrome P-450 CYP3A; D042926:Cytochrome P-450 CYP4A; D010089:Oxidoreductases, N-Demethylating; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine