19] Purification and assay of liver microsomal epoxide hydrase

Abstract

This chapter describes the purification and assay of liver microsomal epoxide hydrase. Microsomal epoxide hydrase catalyzes the hydration of a variety of arene and alkene oxides. The most commonly used substrate is styrene oxide because of its relative stability, commercial availability, and ease of assay. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) shows that the purified liver microsomal epoxide hydrase is nearly homogeneous and contains a single polypeptide with a molecular weight of 53,000-54,000. Other studies indicate that in the absence of SDS, the purified enzyme in aqueous solution exists as high-molecular-weight aggregates. In addition to styrene oxide, the purified epoxide hydrase can also catalyze the hydration of many simple epoxides, K-region and non-K-region arene oxides of polycyclic aromatic hydrocarbons. The assay of these substrates is facilitated by the development of a sensitive and rapid thin-layer chromatographic assay based on the separation of radioactive substrates and their dihydrodiol products on silica gel.