Cytochrome P-450 in insects : 3. Increase in substrate binding by microsomes from phenobarbital-induced house flies

Abstract

Microsomal membranes prepared from the abdomens of two insecticide-susceptible house-fly strains (NAIDM and CSMA) and one insecticide-resistant strain (Rutgers) were examined for evidence of substrate binding by cytochrome P-450. The substrates studied in detail were benzphetamine, nerolidol, and menthone, and to a lesser extent, aldrin and heptachlor. Contrayy to previous reports, type I spectra were obtained with cytochrome P-450 from the susceptible flies. As expected, Rutgers strain P-450 also exhibited type I spectra. The spectra were typical in all cases but one (nerolidol) and were about one-third to one-seventh the size of those obtained with microsomal P-450 from the Rutgers strain. With the exception of those obtained with menthone, substrate-induced spectra were greatly enhanced (about two- to four-fold) with the P-450 from susceptible flies treated with phenobarbital. This treatment did not increase substrate binding by the P-450 from Rutgers flies. In a comparison of the epoxidation of aldrin and heptachlor by induced and noninduced microsomes, it was noted that only the heptachlor epoxidase was increased in all strains. These studies indicate that phenobarbital induction of susceptible flies results in the production of cytochrome P-450 with spectral and enzymatic properties resembling those of resistant flies.