Selective inhibition and kinetics of enzymatic reactions leading to irreversible binding of benzo[a]pyrene to microsomal macromolecules of mouse lung.

Two enzymatic reactions, catalyzed by mouse lung microsomes and distinguishable by selective inhibition and kinetic studies, lead to irreversible binding of benzo[a]pyrene to macromolecules present in vitro reaction systems. One type (low Km) is inducible in the lungs of mice by treatment with benz[a]anthracene and is subject to inhibition by 7,8-benzoflavone. The other type (high Km) is predominant in lungs of untreated mice, but a small amount of low-Km activity is also present. The high-Km activity may be involved in carcinogenesis by benzo[a]pyrene, for it is inhibited by butylated hydroxytoluene, retinol or disulfiram, each of which is reported to have anticarcinogenic activity in intact animals.