title: Inhibitory effects of 1,4-naphthoquinone derivatives on rat cytochrome P4501A1-dependent monooxygenase activity in recombinant yeast microsomes.
abstract: We reported previously that various naphthoquinone derivatives inhibited cytochrome P450-dependent monooxygenase of liver and placenta microsomes [Muto, N. et al. (1987) Biochem. Biophys. Res. Commun. 146, 487-494]. To understand the complex inhibitory behaviors that were observed, it is desirable to study the relationship between structure and inhibitory activity of naphthoquinones in a simplified system containing a single P450 species. In the present study, the inhibitory effects of six derivatives of 1,4-naphthoquinone (hereafter referred to as NQ) on rat cytochrome P4501A1-dependent 7-ethoxycoumarin O-deethylation were examined using yeast microsomes containing overexpressed rat P4501A1. Of these, 2-methyl-5-hydroxy-NQ, 2-methyl-NQ, 2-hydroxy-NQ, and NQ showed competitive inhibition, whereas 5,8-dihydroxy-NQ and 5-hydroxy-NQ showed noncompetitive inhibition. Judging from the inhibitor constant (K(i)), the binding affinity of the four competitive inhibitors for the substrate-binding pocket of P4501A1 is in the order: 2-CH(3)-5-OH-NQ > 2-CH(3)-NQ > NQ >> 2-OH-NQ. On binding with P4501A1, 2-CH(3)-5-OH-NQ, 2-CH(3)-NQ, and NQ induced distinct Type II, Type I, and reverse Type I spectra, respectively. These results indicate that methyl and hydroxyl groups introduced into NQ have unique effects on their binding mode and binding affinity.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. inouye@kais.kyoto-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Inouye
authors.forename: A
authors.initials: A
authors.lastname: Saito
authors.forename: M
authors.initials: M
authors.lastname: Orita
authors.forename: B
authors.initials: B
authors.lastname: Tonomura
authors.forename: H
authors.initials: H
authors.lastname: Imaishi
authors.forename: H
authors.initials: H
authors.lastname: Ohkawa
mesh_terms: D015660:7-Alkoxycoumarin O-Dealkylase / Q000378:metabolism; D000818:Animals; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase; D009285:Naphthoquinones / Q000737:chemistry / Q000494:pharmacology*; D010084:Oxidation-Reduction; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship
chemical_list: D009285:Naphthoquinones; D011994:Recombinant Proteins; D009249:NADP; D015660:7-Alkoxycoumarin O-Dealkylase; D019363:Cytochrome P-450 CYP1A1; D009247:NADH, NADPH Oxidoreductases; D009251:NADPH-Ferrihemoprotein Reductase