A novel pathway for formation of thiol metabolites and cysteine conjugates from cysteine conjugate sulphoxides.

p-Bromothiophenol and S-(p-bromophenyl)-L-cysteine were formed enzymatically from S-(p-bromophenyl)-L-cysteine sulphoxide in the in vitro systems with isolated rat hepatocytes or purified cysteine conjugate beta-lyases. Isotope dilution study with non-radiolabelled carrier of each product suggested the initial liberation of the thiol and subsequent formation of the cysteine conjugate. C-S bond cleavage pathway to liberate sulphenic acid and thiol are postulated to play an important role in in vivo generation of toxic intermediates and products from cysteine conjugates.