Metabolic activation of paracetamol by highly purified forms of cytochrome P-450

The metabolic activation of paracetamol (acetaminophen) to reactive intermediate(s) which bind covalently to proteins was studied in reconstituted systems, employing highly purified preparations of cytochromes P-450 and P-448 isolated from the liver of rats pretreated with phenobarbitone and beta-naphthoflavone respectively. Cytochrome P-448 readily catalysed the activation of paracetamol, but in contrast no activation was observed when cytochrome P-450 was used at the same concentration. Addition of purified epoxide hydratase to the incubation system had no effect on the extent of covalent binding to proteins, indicating that an arene oxide is unlikely to be the reactive intermediate responsible for the paracetamol-induced hepatotoxicity.