Inactivation of Brain and Kidney Aspartate Aminotransferases by S-(1,2-Dichlorovinyl)-L-Cysteine and by S-(1,1,2,2-Tetrafluoroethyl)-L-Cysteine

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Abstract
Long-term exposure to trichloroethylene can cause kidney cancer in experimental animals and humans. In addition, dichloroacetylene (a breakdown product of trichloroethylene) is nephrotoxic and neurotoxic. Both trichloroethylene and dichloroacetylene are metabolized in part to the corresponding cysteine S-conjugate (i.e. S-(1,2-dichlorovinyl)-L-cysteine) which is toxic. Cysteine S-conjugate β-lyases convert S-(1,2-dichlorovinyl)-L-cysteine to pyruvate, ammonia and a reactive fragment that adds to macromolecules, depletes cellular thiols and causes lipid peroxidation. We now show that S-(1,2-dichlorovinyl)-L-cysteine and another nephrotoxic cysteine S-conjugate, S-(1,1,2,2-tetrafluoroethyl)-L-cysteine, inactivate purified cytosolic aspartate aminotransferase and purified alanine aminotransferase. These cysteine S-conjugates also inactivate aspartate aminotransferase in cytosolic and mitochondrial fractions of rat brain and kidney. The present results suggest that some halogenated xenobiotics may be toxic in part through their conversion to the corresponding cysteine S-conjugate which inactivates key pyridoxal 5’-phosphate-containing enzymes.

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