Antibodies against homogeneous epoxide hydratase provide evidence for a single enzyme hydrating styrene oxide and benz(a)pyrene 4,5-oxide

Abstract

THE microsomal enzyme epoxide hydratase (EC 4.2.1.63) is potentially important in the inactivation of metabolically produced epoxides which may be responsible for the mutagenic and/or carcinogenic properties of polycyclic hydrocarbons (for reviews see refs 1–3). Reports^4,5 suggest that the enzyme plays a dual role in (a) producing proximate carcinogens which, after biotransformation to carcinogens by microsomal mono-oxygenase(s) are (b) inactivated by epoxide hydratase. As this enzyme can be induced^6–8, activated^9–10 and inhibited^9–13 it should be useful in studies of the mechanism of chemical carcinogenesis: some inverse correlations have been reported between susceptibility to carcinogenesis by polycyclic hydrocarbons and inducibility of epoxide hydratase at different stages of development in the rat¹⁴. Most investigations of this enzyme^{6–10,15–18}, however, have involved radiometric assay with ³H-styrene oxide as substrate¹⁸. There is evidence that the enzyme(s) responsible for the hydration of this substrate are also involved in hydration of epoxides, derived from polycyclic hydrocarbons^9,19, while other evidence suggests the presence of several epoxide hydratases in the microsomal membrane^7,9,10,19. Thus it was not known whether information about epoxide hydratase obtained with styrene oxide as substrate applied to the enzyme(s) responsible for hydration of epoxides derived from polycyclic hydrocarbons. Using antibodies raised against a homogeneous epoxide hydratase preparation and other criteria described here, we have now found evidence that intact microsomal membranes contain a single enzyme able to hydrate styrene oxide and benz(a)pyrene, 4,5-oxide, a K-region epoxide.