The rabbit pulmonary monooxygenase system: characteristics and activities of two forms of pulmonary cytochrome P-450.

Two forms of rabbit pulmonary cytochrome P-450 have been characterized spectrally and their activities in reconstituted monooxygenase systems investigated. The presence of both microsomal phospholipids and sodium cholate was required to obtain optimum activity. Only one of the cytochromes (I) was active in the N-demethylation of benzphetamine and the O-deethylation of 7-ethoxycoumarin. However, cytochrome II was 20% more active than cytochrome I in the metabolism of benzo[a]pyrene. The profile of the metabolites formed from benzo[a]pyrene indicated that metabolism at the 9 and 10 positions was insignificant in the case of cytochrome I but represented about 40% of the metabolites produced by cytochrome II. The two forms of the cytochrome are present in pulmonary microsomes in approximately equal amounts.