Abstract: CO-difference spectrum of midgut microsome preparation with P450 content of (687±11) pmol/mgPr. Showed absorbance peak at 450nm. O-demethylase of pnitroanisile(pNA) was maximally active at pH 7.8 and temperature 20～25℃. Activity was linear with respect to time for up to 30min, and with respect to enzyme level for up to 5 tissue equivalents/ incubation with 750 g supernatant as enzyme source. Km and Vmax of O-demethylation of pNA estimated were 1.23 mmol/L and 2.54nmol p-nitrophenol formed/mgPr/min. respectively. NADPH was one of the requirements for the O-demethylation of pNA, the activity without external NADPH is 16% as that of with 0.25mmol/L NADPH. 1.5% BSA added in the incubation mixture enhanced (1.2 folds) the production of p-nitrophenol. PBO (1 mmol/L) strikingly (90%) inhibited O-demethylation.1.73 folds induction of O-[demethylase activity was observed by dietary 0.25% PB.

Key words: P450 monooxygenase, O-demethylase activity, induction, phenobarbital, Helicoverpa armigera