PT  - JOURNAL ARTICLE
AU  - Koenigs, Luke L.
AU  - Peter, Raimund M.
AU  - Thompson, Stella J.
AU  - Rettie, Allan E.
AU  - Trager, William F.
TI  - Mechanism-Based Inactivation of Human Liver Cytochrome P450 2A6 by 8-Methoxypsoralen
DP  - 1997 Dec 01
TA  - Drug Metabolism and Disposition
PG  - 1407--1415
VI  - 25
IP  - 12
4099  - http://dmd.aspetjournals.org/content/25/12/1407.short
4100  - http://dmd.aspetjournals.org/content/25/12/1407.full
SO  - Drug Metab Dispos1997 Dec 01; 25
AB  - The P450 2A6 catalyzed 7-hydroxylation of coumarin proceeded with a mean Km of 0.40 (±0.13) μM andVmax of 6.34 nmol/nmol P450/min (36-fold variation) in microsomal preparations from a panel of 12 human livers. Substrate depletion was avoided during the kinetic determinations. 8-Methoxypsoralen (8-MOP) is a potent mechanism-based inactivator of human liver P450 2A6 and reconstituted purified recombinant P450 2A6 based on the following evidence: 1) 8-MOP causes time, concentration, and NADPH-dependent loss of P450 2A6 activity that is not reversed by potassium ferricyanide or extensive dialysis, 2) loss of P450 2A6 activity is associated with a loss of spectrally observable P450, 3) addition of nucleophiles or reactive oxygen scavengers to the incubations does not prevent inactivation of P450 2A6, and 4) 8-MOP-dependent P450 2A6 inactivation is inhibited (concentration dependent) by the addition of a competitive inhibitor (pilocarpine). Inactivation is selective for P450 2A6 at low concentrations of 8-MOP (2.5 μM) after short incubation time periods (3 min) and was characterized by a KI of 0.8 and 1.9 μM in a reconstituted and microsomal system, respectively, and akinact of 1 min−1 and 2 min−1 in a reconstituted and microsomal system, respectively. A substrate depletion partition ratio of 21 was calculated for the inactivation of recombinant P450 2A6. Potency and selectivity suggest that 8-MOP could be a useful tool in vitro for evaluating P450 2A6 activity in various enzyme preparations. The American Society for Pharmacology and Experimental Therapeutics