Spectroscopic identification of ortho-quinones as the products of polycyclic aromatic trans-dihydrodiol oxidation catalyzed by dihydrodiol dehydrogenase. A potential route of proximate carcinogen metabolism

• Published in: The Journal of biological chemistry Vol. 263; no. 4; pp. 1814 - 1820
• Main Authors: Smithgall, T E, Harvey, R G, Penning, T M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 05-02-1988; American Society for Biochemistry and Molecular Biology
• Subjects: Alcohol Oxidoreductases - metabolism; Analytical, structural and metabolic biochemistry; Benzo(a)pyrene - metabolism; Biological and medical sciences; Carcinogens - metabolism; Chemical Phenomena; Chemistry, Physical; Cysteine - metabolism; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Glutathione - metabolism; Magnetic Resonance Spectroscopy; Naphthalenes - metabolism; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Quinones; Purification; Rat; Enzyme; Liver; Quinone; Rodentia; Detoxication; Polycyclic aromatic compound; Cytosol; Thin layer chromatography; Vertebrata; Mammalia; trans-1,2-Dihydrobenzene«-1,2-»diol dehydrogenase; Oxidation; Kinetics; NMR spectrum; Mass spectrometry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)77949-6

The homogeneous dihydrodiol dehydrogenase of rat liver cytosol catalyzes the NADP-dependent oxidation of polycyclic aromatic trans-dihydrodiols, a reaction that may suppress their carcinogenicity provided the products of the reaction are noncarcinogenic. This report demonstrates that the products of naphthalene and benzo[a]pyrene trans-dihydrodiol oxidation are electrophilic o-quinones, which arise via autoxidation of catechols produced from the dihydrodiols by the action of dihydrodiol dehydrogenase. Oxidation of the trans-1,2-dihydrodiol of naphthalene or the 7,8-dihydrodiol of benzo[a]pyrene by the homogeneous rat liver dehydrogenase in 50 mM glycine at pH 9.0 led to the formation of multiple products by TLC, none of which co-migrated with the corresponding o-quinone standards. An identical result was obtained when these standards were incubated with buffer alone, suggesting that o-quinones were formed enzymatically from the dihydrodiols, and then underwent addition reactions with the glycine buffer. In subsequent reactions, the o-quinones formed from the enzymatic oxidation of the trans-dihydrodiols of naphthalene and benzo[a]pyrene were trapped by conducting the reactions in phosphate buffer containing 2-mercaptoethanol. The products of these reactions were identified by 500 MHz nmr and electron impact mass spectrometry as adducts of the 1,2-quinone of naphthalene (m/e M+ = 234) and the 7,8-quinone of benzo[a]pyrene (m/e M+ = 358), which contained mercaptoethanol as a thioether at C-4 and C-10, respectively. Kinetic analysis of the reactivity of the 1,2-quinone of naphthalene showed that the cellular nucleophiles, cysteine and glutathione, react very rapidly with the quinone. The 7,8-quinone of benzo[a]pyrene also reacted with glutathione and cysteine to form water-soluble metabolites, but did not react with adenosine or guanosine. These results suggest that o-quinones formed by enzymatic dihydrodiol oxidation may be effectively scavenged by cellular nucleophiles, resulting in their detoxification.