The metabolism of 1,3-cyclohexadiene by liver microsomal mono-oxygenase

Abstract

1. 1,3-Cyclohexadiene exhibits type I binding spectra with microsomal cytochrome P-450 of either untreated, or phenobarbital- or 3-methylcholanthrene-treated mice. In all cases, two values of K_s can be measured, indicating a different affinity of 1,3-cyclohexadiene towards the cytochrome P-450 species.

2. Mouse-liver microsomal mono-oxygenase metabolizes 1,3-cyclohexadiene to the corresponding mono-epoxide, which is rapidly hydrolysed to trans-3-cyclohexene-1,2-diol and trans-2-cyclohexene-1,4-diol. This hydrolysis was proved to be essentially non-enzymic.

3. A simple gas-chromatographic method was used to quantify the diols and to determine the kinetic constants (K_m and V_max of 1,3-cyclohexadiene mono-epoxidase.

4. Epoxide formation, as determined by diol production from 1,3-cyclohexadiene metabolism, was NADPH- and O₂-dependent and was inhibited by CO and SKF-525A.