Immunochemical characterization of human lung epoxide hydrolases

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Abstract
Immunochemical techniques were used to investigate the biochemical properties of human lung epoxide hydrolases. Two epoxide hydrolases with different immunoreactive properties were identified. These two epoxide hydrolases were found in both cytosolic and microsomal cell fractions. Immunotitration of enzyme activity showed that enzymes that catalyze the hydration of benzo(a)pyrene 4,5‐oxide react with antiserum to rat microsomal epoxide hydrolase; those that hydrate trans‐stilbene oxide do not. Immunotitration and Western blot experiments showed that microsomal and cytosolic benzo(a)pyrene 4,5‐oxide hydrolases have significant structural homology. Immunohistochemical staining of human lung benzo(a)pyrene 4, s‐oxide hydrolase showed that the enzyme is localized primarily in the bronchial epithelium. No cell type‐specific localization was observed. An enzyme‐linked immunosorbent assay was developed which allows direct quantitation of benzo(a)pyrene 4,5‐oxide hydrolase protein. Levels of enzyme protein detected by this assay correlated well with enzyme levels determined by substrate conversion assays.