Rabbit pulmonary cytochrome P-450 monooxygenase system: isozyme differences in the rate and stereoselectivity of...

The rate and stereoselectivity of the cytochrome P-450 (P-450)-dependent oxidation of styrene to styrene 7,8-oxide (SO) were determined in rabbit pulmonary microsomes and with purified rabbit pulmonary P-450 isozymes in reconstituted monooxygenase systems. Stereoselectivity was determined by separation of the diastereomeric SO-glutathione adducts by high-performance liquid chromatography; these four compounds accounted for more than 95% of the SO formed. Pulmonary microsomes preferentially formed (R)-SO [(R)-SO/(S)-SO = 1.6] at a rate of 7.5 nmol of SO formed/min/nmol of P-450. Antibodies to NADPH-P-450 reductase (antireductase) inhibited SO formation in pulmonary microsomes by greater than 98%. In the presence of antibodies to P-450 form 2 (anti-2), pulmonary microsomes oxidized styrene to equal amounts of (R)- and (S)-SO at a rate of 4.2 nmol of SO/min/nmol of total P-450; in the presence of antibodies to P-450 form 5 (anti-5), styrene was stereoselectively oxidized to (R)-SO [(R)-SO/(S)-SO = 2.0] at a rate of 6.5 nmol of SO/min/nmol of total P-450. In reconstituted monooxygenase systems, P-450 forms 2, 5 and 6 oxidized styrene to SO at rates of 10.0, 4.7 and 4.5 nmol of SO formed/min/nmol of P-450, respectively. The relative amounts of (R)-SO and (S)-SO produced were 2.0, 1.0 and 0.9, respectively. Predicted values for rate and stereoselectivity of styrene oxidation by pulmonary microsomes, calculated from the values obtained in the reconstitution experiments and the relative concentrations of the different P-450 isozymes, agreed well with experimentally determined values.