Influence of β-naphthoflavone on 7,12-dimethylbenz(a)anthracene (DMBA) DNA adduction in rainbow trout and on tumorigenicity

Dihydrodiol dehydrogenase (DDH) isoenzymes were purified from rabbit liver (Klein et al., Eur. J. Biochem., 205 (1992) 1155), and the major forms CF-1, CF-5 and CM-2 were tested for their substrate specificity with dihydrodiol and quinone metabolites of polycyclic aromatic hydrocarbons. CF-5, which was shown to correspond to aldehyde reductase in rabbit liver, was found to efficiently oxidize aromatic dihydrodiol metabolites (phenanthrene-1,2-dihydrodiol, benz[a]anthracene-3,4-dihydrodiol) while CF-1, corresponding to carbonyl reductase, and CM-2 were much less active. All three enzyme forms were found to reduce polycyclic K-region o-quinones of benz[a]anthracene, chrysene and benzo[a]pyrene. CF-1 was the least active, and CM-2 was the most active form with reaction velocities of > 10 μmol/min·mg protein. Among a range of synthetic quinones tested, benz[a]anthracene-8,9-quinone and benzo[a]pyrene 9,10-quinone were also good substrates for the three enzymes, as well as p-benzoquinone and naphthalene-1,4-quinone. The reduction of polycyclic o-quinones, but not of p-benzoquinone, by enzyme CM-2 was accompanied by the oxidation of large amounts of NADPH and the consumption of molecular oxygen which is indicative of a redox-cycling process. Thus, the formation of catechol metabolites from dihydrodiols and o-quinones may be catalyzed by the same enzymes in rabbit liver, and the reaction rate of the enzymatic reduction is strongly dependent on the structural type of the polycyclic quinone.