Preparation of rat liver microsomes. All animal experiments were performed according to institutional guidelines. Rats (Wistar, boar, 6-7 weeks old at the beginning of the experiment) were purchased from CLEA Japan. They were treated with 60 mg/5 mL/kg sodium phenobarbital intraperitoneally once daily for 3 days, fasted overnight, and sacrificed by exsanguination from the abdominal aorta. The livers containing 0.15 M KCl at pH 7.4 were in 3 equal volumes of the same buffer and centrifuged (8,500 rpm, 20 min, 4°C) twice. Then the supernatant was collected and centrifuged (34,000 rpm, 80 min, 4°C) to collect rat liver microsomal fractions. Rat liver microsomes contained 71.2 mg protein/mL and 0.479 nmol P450/mg protein. The microsome fraction was diluted in 100 mM sodium phosphate buffer at pH 7.4 for assay.