Acylase-Catalyzed Deacetylation of Haloalkene-Derived Mercapturates

Mercapturates (S-substituted N-acetyl-L-cysteines) are terminal metabolites formed by the glutathione-dependent metabolism of electrophilic xenobiotics, including haloalkenes. Acylases catalyze the hydrolysis of TV-acyl-L-amino acids, including many xenobiotic-derived mercapturates, to give fatty acids and amino acids as products. Although several acylases have been identified, the acylases that catalyze the deacetylation of the haloalkene-derived mercapturates have not been identified and characterized. Acylase I catalyzes the deacetylation of some haloalkene-derived mercapturates, including S-(1,1,2,2-tetrafluoroethy1)-N-acetyl-L-cysteine, S-(2-chloro-l,l,2-trifluoroethyl)-N-acetyl-L-cysteine, and S-(2-bromo-l,l,2-trifiuoroethyl)-Nacetyl-L-cysteine [Uttamsingh, V., et al. (1998) Chem. Res, ToxicoL 11, 800-809]. In the studies presented here, we identified a rat kidney acylase that catalyzed the hydrolysis of the haloalkene-derived mercapturates S-(l,2-dichlorovinyl)-N-acetyl-L-cysteine, S-(l,2,3,4,4-pentachloro-l,3-butadienyl)-N-acetyl-L-cysteine, and S-(2,2-dibromo-l,l-difluoroethyl)-N-acetylL-cysteine. The substrate selectivity and amino acid sequence of the purified rat kidney acylase were studied. Although the sequence of the purified rat kidney acylase was somewhat identical with that ofaspartoacylase, it did not catalyze the hydrolysis of N-acetyl-L-aspartate.