Research article summary (published 12 Jan 2009):

Mechanistic analysis of the inactivation of cytochrome P450 2B6 by phencyclidine: effects on substrate binding, electron transfer, and uncoupling.

Full Abstract

Phencyclidine (PCP) is a mechanism-based inactivator of cytochrome P450 (P450) 2B6. We have analyzed several steps in the P450 catalytic cycle to determine the mechanism of inactivation of P450 2B6 by PCP. Spectral binding studies show that binding of benzphetamine, a type I ligand, to P450 2B6 was significantly affected as a result of the inactivation, whereas binding of the inhibitor n-octylamine, a type II ligand, was not compromised. Binding of these ligands to P450 2B6 occurs in two phases. Stopped-flow spectral analysis of the binding kinetics of benzphetamine to PCP-inactivated 2B6 revealed a 15-fold decrease in the rate of binding during the second phase of the kinetics (k(1) = 5.0 s(-1), A(1) = 30%; k(2) = 0.02 s(-1), A(2) = 70%, where A(2) indicates the fractional magnitude of the second phase) compared with the native enzyme (k(1) = 8.0 s(-1), A(1) = 58%; k(2) = 0.3 s(-1), A(2) = 42%). Analysis of benzphetamine metabolism by the inactivated protein using liquid chromatography/electrospray ionization/mass spectrometry showed that the rates of formation of nor-benzphetamine and hydroxylated nor-benzphetamine were decreased by 75 and 69%, respectively, whereas the rates of formation for amphetamine, hydroxybenzphetamine, and methamphetamine showed slight but statistically insignificant decreases after the inactivation. The rate of reduction of P450 2B6 by NADPH and reductase was decreased by 6-fold as a result of the modification by PCP. In addition, the extent of uncoupling of NADPH oxidation from product formation, a process leading to futile production of H(2)O(2), increased significantly during the metabolism of ethylbenzene as a result of the inactivation.

Author information

Author/s: Shebley, Mohamad (M); Kent, Ute M (UM); Ballou, David P (DP); Hollenberg, Paul F (PF);

Affiliation: Department of Pharmacology, The University of Michigan, Medical Science Research Building III, 1150 W. Medical Center Drive, Ann Arbor, MI 48109-5632, USA.

Grants: CA16954 (Agency:NCI NIH HHS) ; GM20877 (Agency:NIGMS NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't

Journal: Drug metabolism and disposition: the biological fate of chemicals (Drug Metab Dispos), published in United States. (Language: eng)

Reference: 2009-Apr; vol 37 (issue 4) : pp 745-52

Dates: Created 2009/03/20; Completed 2009/07/14;

PMID: 19144770, status: MEDLINE (last retrieved date: 7/24/2009)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MeSH Headings (categories) shown below.

Aryl Hydrocarbon Hydroxylases - antagonists & inhibitors; metabolism Benzphetamine - pharmacokinetics Catalysis Chromatography, Liquid Electron Transport

Enzyme Inhibitors - pharmacology Oxidoreductases, N-Demethylating - antagonists & inhibitors; metabolism Phencyclidine - pharmacology Spectrometry, Mass, Electrospray Ionization Substrate Specificity

Note: Bold headings indicate primary MeSH headings or qualifiers.

Associated Chemicals: Enzyme Inhibitors (0) ; Benzphetamine (156-08-1) ; Phencyclidine (77-10-1) ; Aryl Hydrocarbon Hydroxylases (EC 1.14.14.1) ; S-mephenytoin N-demethylase (EC 1.14.14.1) ; Oxidoreductases, N-Demethylating (EC 1.5.-)

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