PT  - JOURNAL ARTICLE
AU  - Dowers, Tamara S.
AU  - Jones, Jeffrey P.
TI  - KINETIC ISOTOPE EFFECTS IMPLICATE A SINGLE OXIDANT FOR CYTOCHROME P450-MEDIATED <em>O</em>-DEALKYLATION, <em>N</em>-OXYGENATION, AND AROMATIC HYDROXYLATION OF 6-METHOXYQUINOLINE
AID  - 10.1124/dmd.106.010280
DP  - 2006 Aug 01
TA  - Drug Metabolism and Disposition
PG  - 1288--1290
VI  - 34
IP  - 8
4099  - http://dmd.aspetjournals.org/content/34/8/1288.short
4100  - http://dmd.aspetjournals.org/content/34/8/1288.full
SO  - Drug Metab Dispos2006 Aug 01; 34
AB  - One major point of controversy in the area of cytochrome P450 (P450)-mediated oxidation reactions is the nature of the active-oxygen species. A number of hypotheses have been advanced which implicate a second oxidant besides the iron-oxo species designated as compound I (Cpd 1). This oxygen is thought to be either an iron-hydroperoxy species (Cpd 0) or a second spin-state of Cpd 1. Very little information is available on what fraction of P450 oxidations is mediated by the two different oxidants. Herein, we report results on three cytochrome P450-mediated reactions: O-dealkylation, N-oxygenation, and aromatic hydroxylation, which occur by three distinct chemical mechanisms. We have used kinetic isotope effects to test for branching from O-demethylation to N-oxygenation and aromatic hydroxylation, using 6-methoxyquinoline and 2H3-6-methoxyquinoline as substrates for P4501A2. Identical large inverse isotope effects on Vmax/Km are obtained for the formation of both the N-oxide and the phenol. This indicates that all three reactions occur through the same enzyme-substrate complex and, thus, through a single iron-oxygen species. The nature of the iron-oxygen species is less certain but is more likely to be iron-oxo Cpd 1, given the energetics of these reactions. The American Society for Pharmacology and Experimental Therapeutics