Acylation of protein lysines by trichloroethylene oxide

Stable lysine adducts were formed in proteins following reaction with trich loroethylene (TCE) oxide, the major reactive compound generated by the meta bolism of TCE. The order of formation of these adducts is N-6-formyllysine > N-6-(dichloroacetyl)lysine >> N-6-glyoxyllysine, with the ratio being inf luenced by the particular protein. Protein lysine adducts were also analyze d following the enzymatic oxidation of TCE with several different cytochrom e P450 (P450) enzyme systems. The ratio of formyl/dichloroacetyl lysine add ucts was influenced by the enzyme system that was used. Chloral and TCE oxi de formation was more extensive with rat liver microsomes isolated from phe nobarbital-treated rats than with rat microsomes in which P450 2E1 was indu ced by treatment with isoniazid or in human P450 2E1 systems. Glutathione ( GSH) and GSH transferase had inhibitory effects on the reaction of TCE oxid e with albumin, with formylation being atteunated much more than the format ion of dichloroacetyllysine. GSH is likely to react with the reactive acyl chloride intermediates formed from TCE oxide hydrolysis, instead of direct reaction with TCE oxide, as judged by the lack of an effect of GSH on the r ate of decomposition of TCE oxide. Studies with the model enzymes aldolase and glucose-6-phosphate dehydrogenase, both known to have sensitive lysine groups, indicate that TCE oxide has effects similar to known acylating agen ts that form the same adducts; concentrations of TCE oxide (or the model ac ylating agents) in the low-millimolar range were needed for inhibition. The characterization of TCE-derived protein adducts can be used as a basis for consideration of the exposure and risk of TCE to humans. Human P450 2E1 wa s less likely to oxidize TCE to form TCE oxide and protein lysine adducts t han rat P450 2B1, and the difference is rationalized in terms of the influe nce of the protein on chloride migration in an enzyme reaction intermediate .