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J Biol Chem. 1997 Apr 11;272(15):9771-8.

Evidence of proteasome-mediated cytochrome P-450 degradation.

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Laboratory of Clinical Studies, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892-1256, USA.


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.

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