TY - JOUR
T1 - Degradation of cytochrome P450 2E1
T2 - Selective loss after labilization of the enzyme
AU - Tierney, Daniel J.
AU - Haas, Arthur L.
AU - Koop, Dennis R.
N1 - Funding Information:
i This work was supported by Grant AA-08608 from the National Institute on Alcohol Abuse and Alcoholism (D.R.K.) and Grant GM-34009 from the National Institutes of Health (A.L.H.). * To whom correspondence should be addressed at current address: Department of Pharmacology, L-221, Oregon Health Sciences University, 3181 SW. Sam Jackson Park Road, Portland, OR 97201.
PY - 1992/2/14
Y1 - 1992/2/14
N2 - Mechanism-based inactivation of cytochrome P450 can result in the chemical modification of the heme, the protein, or both as a result of covalent binding of modified heme to the protein. In the present study we took advantage of different modes of inactivation of P450 2E1 by CCl4, 1-aminobenzotriazole, or 3-amino-1,2,4-triazole to investigate parameters which target P450 2E1 for proteolysis from the microsomal membrane. Treatment of mice with CCl4 at the point of maximal induction of P450 2E1 after a single oral dose of acetone resulted in the complete loss of P450 2E1-dependent p-nitrophenol hydroxylation and a 75% loss of immunochemically detectable protein within 1 h of administration. Treatment with 1-aminobenzotriazole at the point of maximal induction caused a complete loss of P450 2E1-dependent p-nitrophenol hydroxylation but only a 12% loss of immunochemically detectable protein 1 h after administration. Treatment of mice with 3-amino-1,2,4-triazole caused a rapid loss of both catalytic activity and microsomal p-nitrophenol hydroxylase activity. However, unlike CCl4 treatment, the activity and enzyme level rebounded 5 and 9 h after treatment. The P450 2E1 ligand, 4-methylpyrazole, administered at the point of maximal induction maintained the acetone-induced catalytic and immunochemical level of P450 2E1. These results suggest that differentially modified forms of P450 2E1 show a characteristic susceptibility to degradation. While there are many potential pathways for protein degradation, the loss of P450 2E1 was associated with increased formation of hieh molecular weight microsomal ubiquitin conjugates. The formation of ubiquitin-conjugated microsomal protein which correlates with P450 2E1 loss suggests that ubiquitination may represent a proteolytic signal for the rapid and selective proteolysis of certain labilized conformations of P450 2E1 from the endoplasmic reticulum.
AB - Mechanism-based inactivation of cytochrome P450 can result in the chemical modification of the heme, the protein, or both as a result of covalent binding of modified heme to the protein. In the present study we took advantage of different modes of inactivation of P450 2E1 by CCl4, 1-aminobenzotriazole, or 3-amino-1,2,4-triazole to investigate parameters which target P450 2E1 for proteolysis from the microsomal membrane. Treatment of mice with CCl4 at the point of maximal induction of P450 2E1 after a single oral dose of acetone resulted in the complete loss of P450 2E1-dependent p-nitrophenol hydroxylation and a 75% loss of immunochemically detectable protein within 1 h of administration. Treatment with 1-aminobenzotriazole at the point of maximal induction caused a complete loss of P450 2E1-dependent p-nitrophenol hydroxylation but only a 12% loss of immunochemically detectable protein 1 h after administration. Treatment of mice with 3-amino-1,2,4-triazole caused a rapid loss of both catalytic activity and microsomal p-nitrophenol hydroxylase activity. However, unlike CCl4 treatment, the activity and enzyme level rebounded 5 and 9 h after treatment. The P450 2E1 ligand, 4-methylpyrazole, administered at the point of maximal induction maintained the acetone-induced catalytic and immunochemical level of P450 2E1. These results suggest that differentially modified forms of P450 2E1 show a characteristic susceptibility to degradation. While there are many potential pathways for protein degradation, the loss of P450 2E1 was associated with increased formation of hieh molecular weight microsomal ubiquitin conjugates. The formation of ubiquitin-conjugated microsomal protein which correlates with P450 2E1 loss suggests that ubiquitination may represent a proteolytic signal for the rapid and selective proteolysis of certain labilized conformations of P450 2E1 from the endoplasmic reticulum.
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U2 - 10.1016/0003-9861(92)90358-4
DO - 10.1016/0003-9861(92)90358-4
M3 - Article
C2 - 1309987
AN - SCOPUS:0026546019
SN - 0003-9861
VL - 293
SP - 9
EP - 16
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 1
ER -