Molecular Pharmacology, Vol 13, 342-351, Copyright © 1977 by the American Society for Pharmacology and Experimental Therapeutics

Hepatic Microsomal Epoxide Hydrase: a Sensitive Radiometric Assay for Hydration of Arene Oxides of Carcinogenic Aromatic Hydrocarbons

¹ National Institute of Arthritis, Metabolism, and Digestive Diseases, National Institutes of Health, Bethesda, Maryland 20014
² Department of Biochemistry and Drug Metabolism, Hoffmann-La Roche, Inc., Nutley, New Jersey 07110

A rapid, highly sensitive thin-layer chromatographic assay is described for measurement of epoxide hydrase activity with 11 substrates, including alkene oxides, K-region arene oxides, and non-K-region arene oxides. The highest and lowest specific activities observed were for phenanthrene 9,10-oxide (39 nmoles of product per minute per milligram of protein) and dibenzo[a,h]anthracene 5,6-oxide (0.4 nmole of product per minute per milligram of protein) with liver microsomes from untreated rats. The most sensitive assay for epoxide hydrase activity was the hydration of benzo[a]pyrene 4,5-oxide. Prior treatment of rats with phenobarbital resulted in a 1.7-2.7-fold increase in the rate of hydration for the 11 substrates, whereas 3-methylcholanthrene treatment increased the epoxide hydrase activity approximately 1.3-1.9-fold.

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