p-Nitrophenyl vinyl ether, a novel substrate for the assay of cytochrome P-450 dependent olefinic epoxidation in hepatic microsomes.

p-Nitrophenyl vinyl ether (NPVE) was metabolized to p-nitrophenol and glycolaldehyde via an epoxide by rat hepatic microsomes. The cofactor requirement and effects of monooxygenase inhibitors indicated that the oxidative metabolism of NPVE was mediated by microsomal cytochrome P-450. Epoxide hydrolase plays a minor role, because a strong epoxide hydrolase inhibitor, 3,3,3-trichloropropene oxide, showed a weak inhibitory effect on the p-nitrophenol formation. The epoxy intermediate is so labile that the hydrolysis of the epoxide proceeds mostly nonenzymically even at a neutral pH. Induction experiments suggested that NPVE was susceptible to a wide varieties of cytochrome P-450 species. Thus, a convenient and sensitive method for the assay of olefinic epoxidase activity in hepatic microsomes was developed with NPVE as a substrate.