Epoxide hydrase activity in the flour beetle Tribolium castaneum (Coleoptera, Tenebrionidae)

Abstract

1. 1. Considerable epoxide hydrase (EH) (EC 4.2.1.63) activity is detected in microsomes prepared from homogenates of whole last instar Tribolium castaneum (Herbst) CTC-12 larvae. The enzymatic radioassay used involves hydration of [ 3H]styrene oxide to the corresponding diol. The reaction is linear for at least 30 min and up to 100 μg microsomal protein. The pH optimum is 8.5 and optimal incubation temperature ranges between 30–35°C. Non-enzymatic hydration of styrene oxide (3.2%) occurs during 30 min incubation under optimal assay conditions. 2. 2. EH activity is relatively high in the larval stages and mature adults and low in pharate pupae, pupae and newly emerged adults. 3. 3. The microsomal EH is unaffected by sesamex but it is slightly stimulated by piperonyl butoxide at high concentrations. MGK-264 is inhibitory at high levels. 1,1,1-Trichloro-2,3 epoxypropane, a potent EH inhibitor, is much less effective on T. castaneum enzyme. Ethanol which stimulates EH at low concentrations is inhibitory at high levels. n- Butanol but not other short chain alkanols (at 4%v/v) is inhibitory. 4. 4. Specific activity of microsomal EH hydrating styrene oxide is several fold higher in CTC-12 line than in the CSbb one. This difference, although less dramatic is apparent with juvenile hormone (JH) as substrate. The above is discussed relative to the CTC-12 strain resistance to various insecticides including synthetic JH.