Observation of an unusual electronically distorted semiquinone radical of PCB metabolites in the active site of prostaglandin H synthase-2.

Authors:
Orarat Wangpradit
Orarat Wangpradit
University of Iowa
United States
Edelmiro Moman
Kevin B Nolan
Kevin B Nolan
Royal College of Surgeons in Ireland
Ireland
Garry R Buettner
Garry R Buettner
The University of Iowa
United States
Larry W Robertson
Larry W Robertson
University of Iowa
United States
Gregor Luthe, PhD
Gregor Luthe, PhD
University of Iowa
Gronau, NRW | Germany

Chemosphere 2010 Dec 16;81(11):1501-8. Epub 2010 Sep 16.

Department of Occupational and Environmental Health, The University of Iowa, 100 Oakdale Campus, Iowa City, IA 52242-5000, USA.

The activation of the metabolites of airborne polychlorinated biphenyls (PCBs) into highly reactive radicals is of fundamental importance. We found that human recombinant prostaglandin H synthase-2 (hPGHS-2) biotransforms dihydroxy-PCBs, such as 4-chlorobiphenyl-2',5'-hydroquinone (4-CB-2',5'-H(2)Q), into semiquinone radicals via one-electron oxidation. Using electron paramagnetic resonance (EPR) spectroscopy, we observed the formation of the symmetric quartet spectrum (1:3:3:1 by area) of 4-chlorobiphenyl-2',5'-semiquinone radical (4-CB-2',5'-SQ()(-)) from 4-CB-2',5'-H(2)Q. This spectrum changed to an asymmetric spectrum with time: the change can be explained as the overlap of two different semiquinone radical species. Hindered rotation of the 4-CB-2',5'-SQ()(-) appears not to be a major factor for the change in lineshape because increasing the viscosity of the medium with glycerol produced no significant change in lineshape. Introduction of a fluorine, which increases the steric hindrance for rotation of the dihydroxy-PCB studied, also produced no significant changes. An in silico molecular docking model of 4-CB-2',5'-H(2)Q in the peroxidase site of hPGHS-2 together with ab initio quantum mechanical studies indicate that the close proximity of a negatively charged carboxylic acid in the peroxidase active site may be responsible for the observed perturbation in the spectrum. This study provides new insights into the formation of semiquinones from PCB metabolites and underscores the potential role of PGHS-2 in the metabolic activation of PCBs.

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Source
http://dx.doi.org/10.1016/j.chemosphere.2010.08.041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3622869PMC

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December 2010
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