ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
KL8. Mechanistic Studies of Oxidative Halophenol Dehalogenation by
Heme-Containing Peroxidases
J.H. Dawson, R.L. Osborne, S. Sumithran, M. Coggins, M. Sono
Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street, 29208, Columbia, SC, United
States
e-mail: dawson@sc.edu
Toxic halophenols are produced through industrial processes and pose both environmental risks and health
hazards. Curiously, marine worms in coastal sediments produce noxious halophenols, apparently to deter
predators. To survive in the presence of such poisons, A. ornata uses a catalytically-active globin
dehaloperoxidase to oxidatively dehalogenate halophenols to the corresponding quinones. Two mechanisms for
this reaction have been proposed: a direct two-electron oxygen atom transfer or two successive one-electron
steps via a phenoxy radical. We have also shown that the most versatile heme-containing peroxidase,
Caldariomyces fumago chloroperoxidase (CCPO) - best known as a halogenation catalyst - and the oxygen
transport protein myoglobin both catalyze halophenol dehalogenation. With all three enzymes as well as
horseradish peroxidase (HRP), the mechanism has been probed using para-halophenols, and the product
distribution is consistent with involvement of a phenoxy radical intermediate. Since CCPO and HRP form
relatively stable high-valent ferryl intermediates, we have employed rapid-scan stopped-flow techniques to
differentiate between the two mechanisms. Parallel studies with A. ornata dehaloperoxidase and myoglobin have
also been pursued. Finally, as phenoxy radicals and quinones are known to bind irreversibly to DNA, the ability
of myoglobin to oxidatively dehalogenate halophenols may explain their carcinogenicity.
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