Peroxidase-catalyzed oxidation of 2,4,6-trichlorophenol.
2,4,6-Trichlorophenol (TCP) is an environmental contaminant that is toxic, mutagenic, and carcinogenic. We have investigated peroxidase-catalyzed oxidation of TCP as an alternative pathway of TCP bioactivation using horseradish peroxidase (HRP) as a model peroxidase. TCP was shown to function as a reducing substarte for HRP as evidenced by TCP-dependent, HRP-catalyzed reduction of 5-phenyl-4-penten-1-yl hydroperoxide (PPHP) to its corresponding alcohol. In addition, TCP was shown to undergo hydroperoxide (H2O2, ethyl hydroperoxide, or PPHP)-dependent metabolism as evidenced by electronic absorption spectroscopic analysis of reaction mixtures. A single major product was detected by reverse phase HPLC and was identified as 2,6-dichloro-1,4-benzoquinone (2,6-dichloro-2, 5-cyclohexadiene-1,4-dione, CAS no. 697-91-6) on the basis of electronic absorption spectroscopy, mass spectrometry, and cochromatography with synthetic standard. In addition, HRP-catalyzed oxidation of TCP yielded EPR-detectable phenoxyl radical intermediates whose EPR spectrum consisted of a 1:2:1 triplet characterized by proton hyperfine coupling constants aH(3,5) = 2.35 gauss. Mechanisms for the hydroperoxide-dependent, HRP-catalyzed oxidation of TCP are proposed that are consistent with these results.
Wiese
F W
FW
Division of Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA.
Chang
H C
HC
Lloyd
R V
RV
Freeman
J P
JP
Samokyszyn
V M
VM
D002384:Catalysis; D002733:Chlorophenols / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000378:metabolism*; D009153:Mutagens / Q000378:metabolism*; D010084:Oxidation-Reduction
D002733:Chlorophenols; D009153:Mutagens; D006735:Horseradish Peroxidase; C024564:2,4,6-trichlorophenol