Characteristics of the microsomal N-hydroxylation of benzamidine to benzamidoxime.

1. A simple and fast h.p.l.c. analysis of benzamidoxime formed by microsomal N-hydroxylation of benzamidine is presented which is well suited for the determination of the N-oxygenation activity of microsomal enzymes. 2. Optimal reaction conditions were determined. The apparent Km and Vmax values were, respectively, 1.61 mM and 0.38 nmol benzamidoxime/min per mg protein. 3. The effects of the inducers phenobarbital, 3-methylcholanthrene and benzamidine itself on hepatic benzamidine metabolizing activity in rabbits were determined. 4. Neither superoxide anion nor hydrogen peroxide is directly involved in the N-hydroxylation reaction. 5. The direct involvement of cytochrome P-450 in the N-hydroxylation of benzamidine is supported by the observation that inhibitors of cytochrome P-450, in particular carbon monoxide, markedly decreased the rate of N-oxygenation.