Simplified liquid chromatographic assay for epoxide hydrolase

A simplified liquid chromatographic assay for epoxide hydrolase (E.C. 3.3.2.3) is described. The enzyme substrate employed, 3-(p-nitrophenoxy)-1,2-propene oxide, is commercially available and is readily resolved by reversed-phase liquid chromatography from the enzymatic hydration product, 3-(p-nitrophenoxy)-1,2-propane diol. As little as 100 pmol of the diol can be detected by absorbance monitoring at 315 nm. This assay has been employed to measure epoxide hydrolase in rat liver microsomes from animals treated with the dietary antioxidant, 2(3)-tert.-butyl-4-hydroxyanisole, a known inducer of the enzyme. The assay can also be used to measure rat liver cytosolic epoxide hydrolase.