MP8-dependent oxidative dehalogenation: evidence for the direct formation of 1,4-benzoquinone from 4-fluorophenol by a peroxidase-type of reaction pathway.
The present study shows that MP8 in the presence of H2O2 is able to catalyze the rupture of the stable carbon-fluorine bond of 4-fluorophenol, used as a model substrate for the oxidative dehalogenation reaction. 1,4-Benzoquinone was shown to be the primary reaction product. It is also demonstrated that there was significant [18O] incorporation into the product, 1,4-benzoquinone, from 18O-labelled H2(18)O but not from H2(18)O2. This implies that water participates in the reaction mechanism, and acts as a source for the oxygen atom inserted into the product. It also suggests that the reaction is not a result of direct oxygen transfer from H2O2 through the heme catalyst to the product. Furthermore, ascorbic acid, known to efficiently block MP8-catalyzed peroxidase-type conversions, inhibits the MP8-dependent dehalogenation reaction, most likely because of its ability to reduce the phenoxy radical back to the parent substrate. This observation together with the above-mentioned incorporation of oxygen from the solvent into the benzoquinone product indicates that MP8 dehalogenates 4-fluorophenol and converts it to 1,4-benzoquinone in a peroxidase- and not a P-450-type of reaction mechanism. Overall, our results indicate that the oxidative dehalo genation of para-halogenated phenols, resulting in the formation of benzoquinones, is not specific only for cytochrome P-450 enzymes. Hemoproteins exhibiting peroxidase activity could also play a role in the metabolism of these xenobiotics, resulting in the formation of electrophilic reactive benzoquinone type metabolites.
Osman
A M
AM
Department of Biochemistry, Agricultural University, Wageningen, The Netherlands.
Boeren
S
S
Veeger
C
C
Rietjens
I M
IM
D000818:Animals; D001205:Ascorbic Acid / Q000737:chemistry; D016227:Benzoquinones / Q000378:metabolism*; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D005464:Fluorobenzenes / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006735:Horseradish Peroxidase / Q000737:chemistry; D006736:Horses; D006861:Hydrogen Peroxide / Q000737:chemistry; D007553:Isotope Labeling; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology* / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes; D010544:Peroxidases / Q000737:chemistry* / Q000302:isolation & purification; D010636:Phenols / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014867:Water / Q000737:chemistry
D016227:Benzoquinones; D005464:Fluorobenzenes; D010103:Oxygen Isotopes; D010636:Phenols; D014867:Water; C106880:4-fluorophenol; C004532:quinone; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D010544:Peroxidases; C021799:microperoxidase; D001205:Ascorbic Acid