Cysteine conjugation biotransformation

Once formed, GSH conjugates may be excreted as such (they are best characterized in vitro or in the bile of laboratory animals), but they usually undergo further biotransformation prior to urinary or fecal excretion. Cleavage of the glutamyl and cysteinyl residues by peptidases leave a cysteine conjugate, which is further N-acetylated by cysteine-S-conjugate Af-acetyltransferase (EC 2.3.1.80) to yield an A-acetylcysteine... 

Cysteine conjugates and the twin-ion technique. In addition to studies of glutathione conjugates, we have utilized the twin--ion technique to study reaction mechanisms in reactive metabolite formation from acetylhydrazine and isopropylhydrazine. This technique has proven to be a useful tool when applied to biotransformation studies. Hammar and Holmstedt (15) used the naturally occurring isotopic doublet of chlorine to study the metabolism of chlorpromazine. Morfin et al. (16) were the first to use stable isotope standards in studies of the pathways of testosterone... 

Huyng-Ba, T., Matthey-Doret, W, Fay, L. B., Bel-Rhlid, R. (2003). Generation of thiols by biotransformation of cystein-aldehyde conjugates with baker yeast. J. Agric. Food Chem., 51, 3629-3635. 

Bimer G, Bemauer U, Werner M, and Dekant W (1997) Biotransformation, excretion and nephrotoxicity of ha-loalkene-derived cysteine 5-conjugates. Archives of Toxicology 72 1-8. 

Since MIC is highly reactive, it is not metabolized in the classical sense. Conjugation of MIC with glutathione (GSH) forming an adduct S-(N-methyl-carbamoyl) glutathione, and corresponding cysteine adduct, S-(N-methylcarbamoyl) cysteine appears to represent an important pathway of biotransformation of MIC in the rats exposed to MIC intraper-itoneally. The reaction of MIC with GSH and with cysteine is reversible, and can provide a source of free MIC in the tissues. It is speculated that these carbamate thioester conjugates of MIC may actually contribute to toxic effects of MIC. Similar studies in experimental animals exposed to MIC by the inhalation route have not been reported. 

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