PEROXIDASE-CATALYZED OXIDATION OF 2,4,6-TRICHLOROPHENOL

2,4,6-Trichlorophenol (TCP) is an environmental contaminant that is to xic, mutagenic, and carcinogenic. We have investigated peroxidase-cata lyzed oxidation of TCP as an alternative pathway of TCP bioactivation using horseradish peroxidase (HRP) as a model peroxidase. TCP was show n to function as a reducing substarte for HRP as evidenced by TCP-depe ndent, HRP-catalyzed reduction of 5-phenyl-4-penten-1-yl hydroperoxide (PPHP) to its corresponding alcohol. In addition, TCP was shown to un dergo hydroperoxide (H2O2, ethyl hydroperoxide, or PPHP)-dependent met abolism as evidenced by electronic absorption spectroscopic analysis o f reaction mixtures. A single major product was detected by reverse ph ase HPLC and was identified as 2,6-dichloro-1,4-benzoquinone (2,6-dich loro-2,5-cyclohexadiene-1,4-dione, CAS no. 697-91-6) on the basis of e lectronic absorption spectroscopy, mass spectrometry, and cochromatogr aphy with synthetic standard. In addition, HRP-catalyzed oxidation of TCP yielded EPR-detectable phenoxyl radical intermediates whose EPR sp ectrum consisted of a 1:2:1 triplet characterized by proton hyperfine coupling constants a(H(3,5)) = 2.35 gauss. Mechanisms for the hydroper oxide-dependent, HRP-catalyzed oxidation of TCP are proposed that are consistent with these results.