Optimization of Assay Conditions for Epoxide Metabolizing Enzymes in Trichoplusia Ni

-The optimization of assay conditions for glutathione S-transferase and epoxide hydrolase activities in the cabbage looper (Trichoplusia ni [Hiibner], Lepidoptera; Noctuidae) using trans and cis-stilbene oxides as substrates are reported. Glutathione S-transferase activity was predominantly cytosolic, and it was much greater in the fat body than the midgut. Differences in pH optima and rates of conjugation were seen between the trans and cis isomers of the substrate. In contrast, epoxide hydrolase activity was predominantly microsomal and was highest in the midgut. Patterns of substrate selectivity and pH optima differed between these two tissues. These data reflect the complexity of insect epoxide metabolism and suggest the involvement of multiple forms of these enzymes. Key Word Index: Insect, epoxide, epoxide hydrolase, glutathione S-transferase, trans-stilbene oxide, cis-stilbene oxide, Trichoplusia ni (Hiibner), Lepidoptera, Noctuidae