EPOXIDE HYDROLASE IN THE BULB MITE RHIZOGLYPHUS-ROBINI - PROPERTIES AND INDUCTION

Using styrene oxide as substrate, most of the epoxide hydrolase (EH) a ctivity monitored in the bulb mite Rhizoglyphus robini was associated with the microsomal compartment. The microsomal and cytosolic EHs did not display any significant preference in hydrating trans stilbene oxi de (TSO) and cis stilbene oxide (CSO). The microsomal EH, which has a Km value of 5x10(-5) M and pH optimum of 7.8, was sensitive to ethanol and its activity was inhibited to a moderate extent by 4-fluorochalco ne oxide, TSO, CSO and trans-chalcone oxide at a level of 10(-4) M. Mi crosomal EH was considerably induced (4-5-fold) in mites feeding garli c and onion, or ingesting TSO-impregnated filter papers. Other epoxide s like CSO, 2,4-dichlorostilbene oxide, methyl chalcone oxide and hept achlor epoxide displayed moderate induction levels (1.4-2.6-fold). Of the toxicants assayed only sodium phenobarbital was a potent inducer. Lindane, malathion and DDT did not stimulate EH activity and 3-methyl- cholanthrene was even inhibitory. A decrease in EH activity was observ ed with a number of phytochemicals tested such as sinigrin, flavone, m enthol, trans-beta-carotene, chalcone, allyl sulphide and trans-cinnam ic acid.