Cytochrome P-450 in insects. 6. Age dependency and phenobarbital induction of cytochrome P-450, P-450 reductase, and monooxygenase activities in susceptible and resistant strains of Musca domestica

Abstract

Development and phenobarbital (PB) induction of microsomal cytochrome P-450, cytochrome P-450 reductase, two epoxidation, and two O-demethylation activities were examined in chronologically timed populations of insecticide-susceptible (NAIDM) and -resistant (Rutgers) house flies. Measurements of these enzymes started with the pharate adult stage and ended 5 days following eclosion. Untreated insects of both strains had comparable reductase levels, whereas cytochrome P-450 and associated monooxygenase activities were 1.5-fold or more higher in Rutgers. Maximum induction, as well as toxicity, occurred at a lower PB concentration in NAIDM than Rutgers. The drug caused consistently higher increases in enzymes and activities within 12 hr of starting treatment in both strains. When PB was withdrawn from treated flies (both strains) 48 hr after treatment began, specific activities (product min −1 mg protein −1) in all enzymes returned to control values in 24 hr while metabolic capacity (product min −1 insect −1) achieved control values within 48 hr. The changes in turnover numbers (pmol product min −1 pmol P-450 −1), in conjunction with the differences in the monooxygenation of the four substrates, suggest that PB treatment induced both a quantitative and qualitative change in NAIDM monooxygenation but only a quantitative change in Rutgers monooxygenation.