Tight-binding inhibition by alpha-naphthoflavone of human cytochrome P450 1A2.
Human cytochrome P450 (P450) enzymes exhibit remarkable diversity in their substrate specificities, participating in oxidation reactions of a wide range of xenobiotic drugs. Previously, we reported that alpha-naphthoflavone (ANF) is bound to the recombinant P450 1A2 tightly and stabilizes an overall enzyme conformation. The present study is designed to determine the type of P450 1A2 inhibition exerted by ANF, using two different substrates of P450 1A2, 7-ethoxycoumarin (EOC) and 7-ethoxyresorufin (EOR). ANF is generally known as a competitive inhibitor of the enzyme. However, in our tight-binding enzyme kinetics study, ANF acts as noncompetitive inhibitor in 7-ethoxycoumarin O-deethylation (ECOD) (K(i)=55.0 nM), but as competitive inhibitor in 7-ethoxyresorufin O-deethylation (EROD) (K(i)=1.4 nM). Based on homology modeling studies, ANF is positioned to bind to a hydrophobic cavity next to the active site where it may cause a direct effect on substrate binding. It is agreed with the predicted binding site of ANF in P450 3A4, in which ANF is rather known as a stimulating modulator. Our results suggest that ANF binds near the active site of P450 1A2 and exhibits differential inhibition mechanisms, possibly depending on the molecular structure of the substrate.
Cho
Uhn Soo
US
Graduate School of Biotechnology, Korea University, 5-1 Anam dong, Sungbuk-gu, Seoul 136-701, South Korea.
Park
Eun Young
EY
Dong
Mi Sook
MS
Park
Bum Seok
BS
Kim
Keehyuk
K
Kim
Kyung Hyun
KH
D000595:Amino Acid Sequence; D001571:Benzoflavones / Q000378:metabolism*; D003374:Coumarins / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004791:Enzyme Inhibitors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010078:Oxazines / Q000378:metabolism; D016415:Sequence Alignment; D013379:Substrate Specificity / Q000502:physiology
D001571:Benzoflavones; D003374:Coumarins; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004791:Enzyme Inhibitors; D010078:Oxazines; C017299:7-ethoxycoumarin; C007649:ethoxyresorufin; C011512:alpha-naphthoflavone; D019388:Cytochrome P-450 CYP1A2