Regiospecific oxidation of polycyclic aromatic dihydrodiols by rat liver dihydrodiol dehydrogenase.
Rat liver dihydrodiol dehydrogenase (DDH, E.C. 1.3.1.20) has recently been shown to oxidize the highly carcinogenic benz[a]anthracene-3,4- dihydrodiol in an NADP(+)-dependent reaction to its corresponding catechol. The present study is a systematic investigation of the substrate specificity of the purified enzyme towards synthetic trans-dihydrodiol metabolites of phenanthrene, benz[a]anthracene, chrysene, dibenz[a, h]anthracene and benzo[a]pyrene. DDH exhibited a remarkable regiospecificity of enzymatic catalysis with regard to the site of the dihydrodiol moiety of the parent hydrocarbon. M-region- and, with lower efficiency, bay-region dihydrodiols were found to be good substrates of the enzyme with maximal velocities between 20-80 nmol/min per mg enzyme and Km values in the micromolar range. K-region dihydrodiols were not accepted as substrates. Dihydrodiols situated at the terminal ring of an anthracene-type structure such as benz[a]anthracene-8,9-dihydrodiol as well as the corresponding dihydrodiol epoxides were also not oxidized by DDH at measurable rates. The results provide evidence for a detoxifying role of DDH in the metabolism of the chemical carcinogens benz[a]anthracene, chrysene and dibenz[a, h]anthracene.
Institute of Toxicology, University of Mainz, Germany.
J
J
Klein
A
A
Seidel
H
H
Frank
F
F
Oesch
K L
KL
Platt
D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D000818:Animals; D002384:Catalysis; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D051381:Rats; D013379:Substrate Specificity
D004101:Dihydroxydihydrobenzopyrenes; D010088:Oxidoreductases; D000429:Alcohol Oxidoreductases; C023125:dihydrodiol dehydrogenases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C116788:cis-1,2-dihydro-1,2-dihydroxynaphthalene dehydrogenase