GLUTAMATE-DEHYDROGENASE COVALENTLY BINDS TO A REACTIVE METABOLITE OF ACETAMINOPHEN

The mechanism of the hepatotoxicity of the analgesic acetaminophen is believed to be mediated by covalent binding to protein; however, criti cal targets which effect the toxicity are unknown. It has been shown t hat mitochondrial respiration in vivo is inhibited in mice as early as 1 h following a hepatotoxic dose of acetaminophen, and it is postulat ed that covalent binding to critical mitochondrial proteins may be imp ortant. A time course of mitochondrial proteins stained with anti-acet aminophen 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 p roteins and acetaminophen hepatotoxicity, we have purified and identif ied a 50 kDa mitochondrial protein which becomes covalently bound to a reactive metabolite of acetaminophen. An N-terminal sequence of the 5 0 kDa adduct was 100% homologous with the deduced amino acid sequence of glutamate dehydrogenase. In addition, the purified protein was immu nochemically reactive with rat liver anti-glutamate dehydrogenase. Enz yme activity of glutamate dehydrogenase was significantly decreased in mice 1 h following hepatotoxic treatment with acetaminophen. These da ta suggest that acetaminophen hepatotoxicity may in part be mediated b y covalent binding to glutamate dehydrogenase.