CHARACTERIZATION OF THE MICROSOMAL EPOXIDE HYDROLASE OF HEPATIC MICROSOMES OF THE COMMON DAB, LIMANDA-LIMANDA

Epoxide hydrolase of microsomal membranes of the common dab (Limanda l imanda) has been characterized using p-nitrostyrene oxide as substrate . Under the conditions of assay used, the turnover number with this su bstrate was higher than found for the more frequently used styrene oxi de and steady state kinetics were observed. The enzyme had a K-M of 0. 12 mM and optima for pH and temperature between pH 8-10.2 and 50-60 de grees C respectively. Enzyme activity was unaffected by low concentrat ions of ionic and non-ionic detergents but was inhibited by higher con centrations of Lubrol and Brij. The enzyme protein did not react with monospecific antibodies to rat or human microsomal epoxide hydrolase d uring Western blotting. Large inter-individual variation in enzyme act ivity was found but the enzyme does not appear to be expressed in a ge nder-specific way. Fish were administered a wide range of hydrocarbons which are known to alter the expression of cytochrome P450 1A but the se had no effect other than benzothiophene which caused a small increa se in enzyme activity.