Oxidation of catechol by horseradish peroxidase and human leukocyte peroxidase: reactions of o-benzoquinone and o-benzosemiquinone.
The metabolism of secondary phenolic metabolites of benzene, such as catechol, by peroxidases represents one possible mechanism underlying benzene-induced myelotoxicity. The oxidation of catechol by horseradish peroxidase and peroxidases present in human leukocytes was therefore examined. Peroxidatic oxidation resulted in o-benzoquinone production, which was characterized as its bromothiophenol adduct. o-Benzoquinone-glutathione conjugates were formed during peroxidatic oxidation of catechol in the presence of glutathione. Both mono- and diglutathione conjugates were detected. As much as 80% of catechol removed during peroxidatic oxidation could be recovered as glutathione conjugates of o-benzoquinone. Glutathione had no inhibitory effect on the removal of catechol during peroxidatic oxidation. In the presence of divalent cations (Mg2+, Zn2+), however, which slow the rate of o-semiquinone disproportionation, glutathione was found to inhibit catechol removal. This suggests that in the absence of stabilizing metal, reduction of the o-benzosemiquinone radical by glutathione cannot compete with other rapid reactions of the radical such as disproportionation. No interaction of the o-benzosemiquinone radical with oxygen could be detected even in the presence of stabilizing metals or superoxide dismutase which inhibits the reverse reaction of the SQ + O2 in equilibrium Q + O.2 equilibrium. Thus, under physiological conditions, glutathione and oxygen would not be expected to reduce or oxidize respectively the o-benzosemiquinone radical. These data show that the generation of thiol conjugates of o-benzoquinone can be used as probes of peroxidatic oxidation of catechol.
Sadler
A
A
Molecular and Environmental Toxicology Program, School of Pharmacy, University of Colorado, Boulder 80309.
Subrahmanyam
V V
VV
Ross
D
D
D016227:Benzoquinones; D002396:Catechols / Q000378:metabolism*; D005978:Glutathione / Q000494:pharmacology; D006735:Horseradish Peroxidase / Q000494:pharmacology*; D006801:Humans; D007962:Leukocytes / Q000201:enzymology; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000494:pharmacology*; D010544:Peroxidases / Q000494:pharmacology*; D011809:Quinones / Q000378:metabolism*
D016227:Benzoquinones; D002396:Catechols; D011809:Quinones; C025232:semiquinone radicals; C004532:quinone; D006735:Horseradish Peroxidase; D010544:Peroxidases; D009195:Peroxidase; D005978:Glutathione; C034221:catechol