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

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 When PB was withdrawn from treated flies (both strains) 48 hr after treatment began, specific activities (product min^?1 mg protein^?1) in all enzymes returned to control values in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.     

Cytochrome P-450 in insects: 2. Multiple forms in the flesh fly (Sarcophaga bullata,Parker), and the blow fly (Phormia regina (Meigen))

Microsomes prepared from the abdomens of the flesh fly (Sarcophaga bullata, Parker) and the blow fly (Phormia regina (Meigen)) contain approximately one-fifth and one-eighth as much cytochrome P-450, respectively, as those prepared from house fly (Musca domestica, L.) abdomens. These values correlate well with the microsomal aldrin epoxidase activity of the three species and with their respective susceptibilities to the insecticide, propoxur. When the microsomes of the flesh fly and the blow fly are solubilized by treatment with deoxycholate and resolved by ion-exchange chromatography on DEAE-cellulose and hydroxylapatite, four chromatographically distinct fractions containing cytochrome P-450 are obtained. Spectrophotometric assays of the cytochrome P-450 in these fractions indicate purifications of two-to sixfold for the flesh fly hemoprotein and two-to eightfold for that of the blow fly. SDS-Polyacrylamide gel electrophoresis of the four column fractions from the flesh fly microsomes indicates that six hemoproteins in the 40,000–60,000 molecular weight range are present. In similar experiments with blow fly fractions containing approximately the same amount of cytochrome P-450 no high molecular weight hemoproteins could be detected. This result is interpreted, with other evidence, as an indication of the greater instability of the blow fly hemoprotein. The results indicate that multiple forms of cytochrome P-450 are present in both species but there is insufficient data on which to estimate the number of such forms.