Glutamate Dehydrogenase Covalently Binds to a Reactive Metabolite of Acetaminophen

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Abstract
The mechanism of the hepatotoxicity of the analgesic acetaminophen is believed to be mediated by covalent binding to protein; however, critical targets which effect the toxicity are unknown. It has been shown that mitochondrial respiration in vivo is inhibited in mice as early as 1 h following a hepatotoxic dose of acetaminophen, and it is postulated that covalent binding to critical mitochondrial proteins may be important. A time course of mitochondrial proteins stained with anti-acetaminophen in an immunoblot detected two major adducts of 50 and 67 kDa as early as 30 min after a hepatotoxic dose of acetaminophen in mice. To further understand the role of covalent binding to mitochondrial proteins and acetaminophen hepatotoxicity, we have purified and identified a 50 kDa mitochondrial protein which becomes covalently bound to a reactive metabolite of acetaminophen. An N-terminal sequence of the 50 kDa adduct was 100% homologous with the deduced amino acid sequence of glutamate dehydrogenase. In addition, the purified protein was immunochemically reactive with rat liver anti-glutamate dehydrogenase. Enzyme activity of glutamate dehydrogenase was significantly decreased in mice 1 h following hepatotoxic treatment with acetaminophen. These data suggest that acetaminophen hepatotoxicity may in part be mediated by covalent binding to glutamate dehydrogenase.