Rapid and sensitive enzyme-linked immunosorbent assay for the microsomal epoxide hydrolase

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Abstract
A rapid and sensitive indirect enzyme-linked immunosorbent assay (ELISA) was developed for micrsomal epoxide hydrolase of rat liver. The assay, which is easily and readily performed, is significantly more sensitive than most enzymatic epoxide hydrolase assays routinely used and electroimmunoassays previously developed. The limit of sensitivity of the ELISA is between 2–5 ng of microsomal epoxide hydrolase. Using the ELISA microsomal epoxide hydrolases of mouse and rat liver were shown to be antigenically very similar, while microsomal epoxide hydrolases of guinea pig, monkey and human liver are antigenically distinct from those of rat and mouse. The ELISA developed here is capable of detecting microsomal epoxide hydrolase of rat and mouse liver even when significant enzymatic activity is lost. These results indicate that the antigenic sites recognized by the antibodies used are distinct from the catalytic site of the epoxide hydrolase. Approximately 1.9% of rat microsomal protein was quantified as microsomal epoxide hydrolase by the ELISA. Low levels of microsomal epoxide hydrolase were also detected in rat liver cytosol (∼0.02% of the cytosolic protein) demonstrating that microsomal epoxide hydrolase is not totally membrane bound or that an immunologically related protein occurs in the cytosol of normal rat liver. The ELISA developed here will be valuable in investigating further the role of microsomal epoxide hydrolase.