Details

Autor(en) / Beteiligte

• Penning, Trevor M
• Ohnishi, S. Tsuyoshi
• Ohnishi, Tomoki
• Harvey, Ronald G

Titel

Generation of Reactive Oxygen Species during the Enzymatic Oxidation of Polycyclic Aromatic Hydrocarbon trans-Dihydrodiols Catalyzed by Dihydrodiol Dehydrogenase

Ist Teil von

• Chemical research in toxicology, 1996-01, Vol.9 (1), p.84-92

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

1996

Quelle

MEDLINE

Beschreibungen/Notizen

• Dihydrodiol dehydrogenase (DD; EC 1.3.1.20) catalyzes the oxidation of polycyclic aromatic hydrocarbon (PAH) trans-dihydrodiols (proximate carcinogens) to catechols which rapidly autoxidize to yield o-quinones (Smithgall, T. E., Harvey, R. G., and Penning, T. M. (1988) J. Biol. Chem 263, 1814−1820). Although this pathway suppresses the formation of the PAH anti- and syn-diol epoxides (ultimate carcinogens), the process of autoxidation is anticipated to yield reactive oxygen species (ROS). We now show that the NADP+ dependent oxidation of (±)-trans-1,2-dihydroxy-1,2-dihydronaphthalene (Npdiol) and (±)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (Bpdiol) catalyzed by homogeneous DD is accompanied by the consumption of molecular oxygen and the production of H2O2. With both trans-dihydrodiol substrates, oxygen consumption was stoichiometric with H2O2 production consistent with the reaction:  QH2 + O2 = H2O2 + Q, where QH2 is the catechol and Q is the o-quinone. Using Npdiol or Bpdiol as substrates, a burst of superoxide anion production is catalyzed by DD which can be detected as the rate of cyt c reduction that is inhibited by superoxide dismutase. Using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as spin-trapping agent, secondary spin adducts corresponding to DMPO-CH3 were formed during the enzymatic oxidation of Npdiol and Bpdiol. The formation of the CH3 • radical arises from the OH• attack of DMSO, which was used as cosolvent. These spin adducts were attenuated by superoxide dismutase and catalase, implying that O2 -• and H2O2 are obligatory for the formation of DMPO-CH3. It is proposed that O2 -• is the radical that propagates autoxidation and that the resultant H2O2 undergoes Fenton chemistry to produce the OH• radical. Identical spin adducts were observed using a superoxide anion generating system (hypoxanthine/xanthine oxidase) and DMPO as spin-trapping agent in the presence of DMSO. The ability of DD to generate ROS during the oxidation of PAH trans-dihydrodiols (proximate carcinogens) may have important implications for tumor initiation and promotion.