Distribution of cysteine conjugate beta-lyase in gastrointestinal bacteria and in the environment.

A cysteine conjugate beta-lyase was detected in 24 of 43 gastrointestinal bacteria tested, and from mixed populations of bacteria obtained from lake, river and soil samples. These bacterial cysteine conjugate beta-lyases catalyse the cleavage of the thioether linkage of both an S-alkyl- and an S-aryl-linked cysteine conjugate (2-S-cysteinyl-N-isopropylacetanilide (cysteine conjugate of propachlor) and S-(2-benzothiazolylcysteine), respectively). A cysteine conjugate beta-lyase was isolated from Eubacterium limosum at levels at least 16-fold greater than those from any other gastrointestinal bacterial tested. This enzymic activity was present from the late lag phase through the stationary phase of growth of the bacteria. Maximum activity occurred in the mid log phase. A cysteine conjugate beta-lyase isolated from animal and plant tissues cleaved only the S-aryl-linked cysteine conjugate (S-(2-benzothiazolyl)cysteine) and generally had less enzymic activity than enzymes isolated from the bacteria. Glutathione-S-transferase activity was not detected in the 43 gastrointestinal bacteria tested, except for a low level (0.6 nmol/min per mg) of activity in Escherichia coli. No S-methyl transferase activity was detected in the gastrointestinal bacteria or mixed populations of bacteria tested.