Rat microsomal suspension was prepared using the method described in our previous paper (Kumar et al., 2011). Briefly, excised SD rat livers were minced with scissors and homogenized in a solu- tion composed of 0.32 M sucrose and 1 mM dithiothreitol in 0.02 M phosphate buffer at pH 6.5. The liver homogenate was further cen- trifuged twice at 4500 × g at 0 ◦C for 30 min each time. All of the supernatants were collected and kept at −50 ◦ C until used as an enzyme source.