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 α-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) (Ki=55.0 nM), but as competitive inhibitor in 7-ethoxyresorufin O-deethylation (EROD) (Ki=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.
|Number of pages
|Biochimica et Biophysica Acta - Proteins and Proteomics
|Published - 2003 May 30
Bibliographical noteFunding Information:
Part of this study was supported by a grant (#HMP-98-D-5-0046) from the R&D Project, the Ministry of Health and Welfare, Korea. USC, EYP, and BSP also received additional support from the Brain Korea 21 program of the Ministry of Education.
- Human cytochrome P450 1A2
- Tight-binding inhibition
ASJC Scopus subject areas
- Analytical Chemistry
- Molecular Biology