Abstract

The relationship between chemical structure and the difference spectra obtained with microsomes from the abdomens of insecticide-susceptible and -resistant houseflies was examined. The presence of a "sterically accessible" nitrogen atom with a pair of nonbonded electrons or an accessible oxygen atom in certain configurations appears to be of primary importance in the formation of type II difference spectra. However, factors such as steric hindrance and electronic configuration determine the spectral magnitude. The absorption maxima and minima vary with the ligand and the source of the cytochrome P-450. These data are discussed with reference to possible binding sites and to selectivity of ligands for them.