Biochemical and genetic analysis of epoxide-metabolizing enzymes in susceptible and resistant house flies, Musca domestica L

Abstract

Microsomal and cytosolic activities of glutathione S-transferase (GST) and epoxide hydrolase (EH) toward trans- and cis-stilbene oxides (TSO and CSO, respectively) were measured in homogenates of the house fly ( Musca domestica L.) from strains that are either susceptible or metabolically resistant to insecticides. GST activity was detectable with CSO but not with TSO. Thus, the substrate selectivity of house fly GSTs differs from that in mammals and some other insects where the conjugation of both TSO and CSO has been measured previously. High levels of microsomal and cytosolic GST activities were present in the resistant, but not in the susceptible, strain. The genes controlling these high GST activities from both subcellular fractions were mapped to chromosome II. In contrast, no differences in levels, substrate selectivity, or subcellular locale of EH activity were detected between susceptible and metabolically resistant flies. These data suggest that EH activity is not coordinately regulated with GST or other enzymes relating to metabolic resistance in the house fly. If multiple resistance results from the coordinate regulation of detoxifying enzymes, the fact that EH is controlled differently may allow insecticides that contain epoxides and/or are activated by epoxidation to be used against insect populations where multiple resistance has arisen.