title: Mechanisms of acetaminophen oxidation to N-acetyl-P-benzoquinone imine by horseradish peroxidase and cytochrome P-450.
abstract: Horseradish peroxidase rapidly catalyzed the H2O2-dependent polymerization of acetaminophen. Acetaminophen polymerization was decreased and formation of GSSG and minor amounts of GSH-acetaminophen conjugates were detected in reaction mixtures containing GSH. These data suggest that horseradish peroxidase catalyzed the 1-electron oxidation of acetaminophen and that GSH decreased polymerization by reducing the product, N-acetyl-p-benzosemiquinone imine, back to acetaminophen. Analyses of reaction mixtures that did not contain GSH showed N-acetyl-p-benzoquinone imine formation shortly after initiation of reactions. When GSH was added to similar reaction mixtures at various times, 3-(glutathion-S-yl)-acetaminophen was formed. The formation and disappearance of this product were very similar to N-acetyl-p-benzoquinone imine formation and were consistent with the disproportionation of 2 mol of N-acetyl-p-benzosemiquinone imine to 1 mol of N-acetyl-p-benzoquinone imine and 1 mol of acetaminophen followed by the rapid reaction of N-acetyl-p-benzoquinone imine with GSH to form 3-(glutathion-S-yl)acetaminophen. When acetaminophen was incubated with NADPH, oxygen and hepatic microsomes from phenobarbital-pretreated rats, 1.2 nmol 3-(glutathion-S-yl)acetaminophen/nmol cytochrome P-450/10 min was formed. Formation of polymers was not observed indicating that N-acetyl-p-benzoquinone imine was formed via an overall 2-electron oxidation rather than a disproportionation reaction. However, when cumene hydroperoxide was replaced by NADPH in microsomal incubations, polymerization was observed suggesting that cytochrome P-450 might also catalyze the 1-electron oxidation of acetaminophen.
mesh_terms: D000082:Acetaminophen / Q000378:metabolism*; D000818:Animals; D001555:Benzene Derivatives / Q000378:metabolism; D016227:Benzoquinones; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000378:metabolism*; D007097:Imines / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008862:Microsomes, Liver / Q000201:enzymology; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001555:Benzene Derivatives; D016227:Benzoquinones; D007097:Imines; D046911:Macromolecular Substances; D000082:Acetaminophen; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D006735:Horseradish Peroxidase; D010544:Peroxidases; C028473:N-acetyl-4-benzoquinoneimine; D005978:Glutathione; C007164:cumene hydroperoxide