title: Cysteine conjugate beta-lyase in the gastrointestinal bacterium Eubacterium limosum.
abstract: A cysteine conjugate beta-lyase (beta-lyase) from the gastrointestinal bacterium Eubacterium limosum has been isolated and characterized. This organism has the highest specific activity for cysteine conjugate beta-lyase of the gastrointestinal bacteria studied. The beta-lyase was found to cleave the thioether linkage of S-alkyl- and S-aryl-L-cysteine conjugates. Stoichiometric amounts of 2-mercaptobenzothiazole, pyruvic acid, and ammonia were produced from the beta-lyase cleavage of S-(2-benzothiazolyl)-L-cysteine. The enzyme activity was inhibited by hydroxylamine, iodoacetic acid, or KCN. The enzyme appears to be a 75,000-Da dimer of two 38,000-Da subunits. A natural substrate, cystathionine, was cleaved by this enzyme, indicating that this beta-lyase has beta-cystathionase activity. These data suggest that a beta-cystathionase from E. limosum may be an important enzyme in the metabolism of a wide range of cysteine conjugates of xenobiotics to thiol-containing products.
mesh_terms: D000818:Animals; D013437:Carbon-Sulfur Lyases; D002855:Chromatography, Thin Layer; D004064:Digestive System / Q000382:microbiology*; D005051:Eubacterium / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008190:Lyases / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D008970:Molecular Weight
chemical_list: D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase