title: Non-K-region o-quinones as enzyme-generated inactivators of dihydrodiol dehydrogenase.
abstract: Homogeneous 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase from rat liver cytosol catalyzes the NAD(P)+-dependent oxidation of non-K-region trans-dihydrodiols of polycyclic aromatic hydrocarbons, many of which are proximate carcinogens. These reactions proceed with Km values in the millimolar range to yield highly reactive o-quinones that can be trapped as thioether adducts [Smithgall, T. E., Harvey, R. G., & Penning, T. M. (1988) J. Biol. Chem. 263, 1814-1820]. The enzymatically generated o-quinones, e.g., naphthalene-1,2-dione and benzo[a]pyrene-7,8-dione are potent inhibitors of the dehydrogenase, yielding IC50 values of 5.0 and 10.0 microM, respectively. Naphthalene-1,2-dione was found to be an efficient irreversible inhibitor of the enzyme and can inactivate equimolar concentrations of the dehydrogenase, yielding a t 1/2 for the enzyme of 10 s or less. By contrast (+/-)-trans-1,2-dihydroxy-1,2-dihydronaphthalene promotes a slower inactivation of the dehydrogenase, yielding a Kd of 70 microM and a limiting rate constant that corresponds to a t 1/2 at saturation of 23.2 min. Inactivation by this dihydrodiol has an obligatory requirement for NADP+. Examination of the kcat for the oxidation of (+/-)-trans-1,2-dihydroxy-1,2-dihydronaphthalene yields a partition ratio for the dihydrodiol of 200,000, suggesting that alkylation from the parent dihydrodiol is a rare occurrence. Benzo[a]pyrene-7,8-dione, which is the product of the enzymatic oxidation of (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, also promotes a time- and concentration-dependent inactivation of the dehydrogenase.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia 19104-6084.
authors.forename: T M
authors.initials: TM
authors.lastname: Penning
authors.forename: R B
authors.initials: RB
authors.lastname: Sharp
authors.forename: T E
authors.initials: TE
authors.lastname: Smithgall
mesh_terms: D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors*; D000478:Alkylation; D000818:Animals; D005978:Glutathione / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D009249:NADP / Q000378:metabolism / Q000494:pharmacology; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011809:Quinones / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013329:Structure-Activity Relationship
chemical_list: D011809:Quinones; D009249:NADP; 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; D005978:Glutathione