Epoxide hydrolase activity on juvenile hormone in Manduca sexta

Abstract

As suggested by their mechanism-derived IUPAC nomenclature, epoxide hydrolases (EH) are characterized by the hydrolysis of epoxides. In this study EH activity from M. sexta was monitored in cell fractions from fat body and integument using juvenile hormone III (JH) as a substrate. Experiments were conducted to identify a suitable detergent and detergent concentration for solubilization of microsomal and mitochondrial juvenile hormone epoxide hydrolase (JHEH) activity. Triton X-100 efficiently released total and specific JHEH activity from membranes. A pH optimum range was determined for EH activity in cell fractions from different tissue sources. Potential inhibitors of JHEH activity were tested. One of the better inhibitors was a glycidol analog of JH. EH activity on JH III was compared to activity on JH III bisepoxide, cis-stilbene oxide, and trans-stilbene oxide. JHEH tolerance to detergents, salt, and elevated temperature was investigated. As observed in a similar study on D. melanogaster, the effect of inhibitors, substrates, detergents, salt and temperature suggests the presence of EH isozymes. Polyethylene glycol and ammonium sulfate were used to precipitate JHEH activity from solubilized microsomes and cytosol.