Purification and characterization of C-S lyase from Fusobacterium varium. A C-S cleavage enzyme of cysteine conjugates and some S-containing amino acids.

An enzyme responsible for the carbon-sulfur bond cleavage of various S-aryl, S-aralkyl, and S-alkyl cysteines has been purified about 270-fold from Fusobacterium varium. Incubation of a cysteine conjugate of p-bromobenzene with the enzyme yielded equimolar amounts of p-bromobenzenethiol, pyruvic acid, and ammonia, indicating that the carbon-sulfur bond cleavage proceeds via an alpha, beta-elimination reaction. The enzyme activity was inhibited either by hydroxylamine or KCN and stabilized by pyridoxal phosphate, which probably acted as cofactor. The broad substrate spectrum of this enzyme suggested an important role of the intestinal microflora in the in vivo formation of methylthio-containing metabolites of various xenobiotics.