Cytochrome P-450 Optical Difference Spectra of Insecticides. A Comparative Study

The cytochrome P-450 optical difference spectra of insecticides were examined using hepatic microsomes from sheep, rabbit, rat, and mouse as well as abdominal microsomes from insecticideresistant (Fc) and insecticide-susceptible (CSMA) house flies. The results generally conform to the hypothesis that type II binding spectra are elicited by compounds containing a nitrogen atom with a sterically accessible pair of nonbonded electrons and, in addition, certain compounds with nucleophilic oxygen atoms. Other compounds generally exhibit type I spectral binding or do not form detectable spectra. Exceptions include certain pyrethroids which, while giving typical type I difference spectra with mammalian microsomes, gave rise to an unusual spectrum in insects, one with a peak at 415-418 nm and trough at 445-447 nm. Rotenone also gave rise to unusual difference spectra with hepatic microsomes of sheep and rabbit. Differences in the ratios of spectral size between species indicate that qualitative differences in the cytochrome P-450 of different species are common.