Liver microsomal DT diaphorase: noninvolvement in hydroxylation of benzo(a)pyrene.

A highly purified reconstituted system isolated from the microsomes of 3-methylcholanthrene-treated rats consisting of cytochrome P-448, NADPH-cytochrome $\text{c}$ reductase and synthetic dilauroyl phosphatidylcholine had no DT diaphorase activity, but hydroxylated benzoa]pyrene at a faster rate than microsomes from 3-methylcholanthrene-treated rats. DT diaphorase purified from liver microsomes of 3-methylcholanthrene-treated rats when added to this reconstituted system did not stimulate or inhibit benzoa]pyrene hydroxylation, nor could it replace or NADPH-cytochrome $\text{c}$ reductase in supporting the reaction. We therefore conclude that microsomal DT diaphorase is not involved in microsomal hydroxylation of benzoa]pyrene to its phenolic products despite the observation that both DT diaphorase activity and the hydroxylation of benzoa]pyrene are induced by 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-$\text{p}$-dioxin