Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

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Penning, T.M. et al.

Non-K-region o-quinones as enzyme-generated inactivators of dihydrodiol dehydrogenase.

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)[1]

References

Non-K-region o-quinones as enzyme-generated inactivators of dihydrodiol dehydrogenase. Penning, T.M., Sharp, R.B., Smithgall, T.E. Biochemistry (1989) [Pubmed]

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