
<ArticleTitle>Conjugation of haloalkanes by bacterial and mammalian <prot>glutathione transferase</prot>s: mono- and vicinal dihaloethanes.</ArticleTitle>
<AbstractText><prot>Glutathione (GSH) transferase</prot>s are generally involved in the detoxication of xenobiotic chemicals. However, conjugation can also activate compounds and result in DNA modification. Activation of 1,2-dihaloethanes (BrCH(2)CH(2)Br, BrCH(2)CH(2)Cl, and ClCH(2)CH(2)Cl) was investigated using two mammalian <prot>theta class GSH transferase</prot>s (rat <prot>GST 5-5</prot> and human <prot>GST T1</prot>) and a bacterial <prot>dichloromethane dehalogenase</prot> (<prot>DM11</prot>). Although the literature suggests that the bacterial <prot>dehalogenase</prot> does not catalyze reactions with CH(3)Cl, ClCH(2)CH(2)Cl, or CH(3)CHCl(2), we found a higher enzyme efficiency for <prot>DM11</prot> than for the mammalian <prot>GSH transferase</prot>s in conjugating CH(3)Cl, CH(3)CH(2)Cl, and CH(3)CH(2)Br. Enzymatic rates of activation of 1,2-dihaloethanes were determined in vitro by measuring S,S-ethylene-bis-GSH, the major product trapped by nonenzymatic reaction with the substrate GSH. Salmonella typhimurium TA 1535 systems expressing each of these <prot>GSH transferase</prot>s were used to determine mutagenicity. Rates of formation of S,S-ethylene-bis-GSH by the <prot>GSH transferase</prot>s correlated with the mutagenicity determined in the reversion assays for the three 1,2-dihaloethanes, consistent with the view that half-mustards are the mutagenic products of the <prot>GSH transferase</prot> reactions. Half-mustards [S-(2-haloethyl)GSH] containing either F, Cl, or Br (as the leaving group) were tested for their abilities to induce revertants in S. typhimurium, and rates of hydrolysis were also determined. <prot>GSH transferase</prot>s do not appear to be involved in the breakdown of the half-mustard intermediates. A halide order (Br  Cl) was observed for both <prot>GSH transferase</prot>-catalyzed mutagenicity and S,S-ethylene-bis-GSH formation from 1,2-dihaloethanes, with the single exception (both assays) of BrCH(2)CH(2)Cl reaction with <prot>DM11</prot>, which was unexpectedly high. The lack of substrate saturation seen for conjugation of dihalomethanes with <prot><prot>GST</prot>s 5-5</prot> and T1 was also observed with the mono- and 1,2-dihaloethanes [Wheeler, J. B., Stourman, N. V., Thier, R., Dommermuth, A., Vuilleumier, S., Rose, J. A., Armstrong, R. N., and Guengerich, F. P. (2001) Chem. Res. Toxicol. 14, 1118-1127], indicative of an inherent difference in the catalytic mechanisms of the bacterial and mammalian <prot>GSH transferase</prot>s.</AbstractText>
