Differences in the microsomal P450 monooxygenase system and its inducibility by pentamethylbenzene (PMB) and naphathalene (NA) were investigated in midgut and fatbody tissues of the cotton bollworm, Helicoverpa armigera (Boddie), larvae. Orthogonal array design was used to establish the optimal conditions for measuring Aldrin epoxidation (AE). The optima for AE were similar for the midgut and the fatbody, at a temperature of 30°C, pH 7.4, and a time of 10 min. In comparison to fatbody, the midgut had higher levels of total cytochrome P450s, p-nitroanisole O-demethylation (ODM) and AE. In vivo administration of 0.2% PMB or 0.2% NA resulted in higher microsomal protein content and levels of total cytochrome P450 as well as the two examined monooxygenase activities. Total cytochrome P450 and ODM activity were induced to a greater degree in the fatbody. In the midgut, PMB was significantly more effective on ODM than NA. Differences existed in SDS-PAGE profiles between the midgut and the fatbody. The induction of the midgut with PMB and of the fatbody with NA and PMB resulted in marked intensification of the protein bands with molecular masses of 59,100, 53,400, 50,400 Da.
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Vol. 96 • No. 4