RT Journal Article
SR Electronic
T1 Mechanism-Based Inactivation of Human Liver Cytochrome P450 2A6 by 8-Methoxypsoralen
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1407
OP 1415
VO 25
IS 12
A1 Luke L. Koenigs
A1 Raimund M. Peter
A1 Stella J. Thompson
A1 Allan E. Rettie
A1 William F. Trager
YR 1997
UL http://dmd.aspetjournals.org/content/25/12/1407.abstract
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