Cysteine conjugate β-lyase in the gastrointestinal bacterium Fusobacterium necrophorum

Abstract

1. A cysteine conjugate β-lyase from the anaerobic gastrointestinal bacterium Fusobacterium necrophorum was purified 51-fold by heat treatment, ammonium sulphate fractionation, gel-filtration chromatography, and anion-exchange chromatography. 2. This enzyme catalyses the cleavage of the thioether linkage in cysteine conjugates of the following S-alkyl- or S-aryl-linked compounds: cysteine conjugate of propachlor (2-S-cysteinyl-N-isopropylacetanilide); 1,2-dihydro-1-hydroxy-2-S-cysteinylnaphthalene and S-(2-benzothiazolyl)cysteine. 3. 2-Mercapto-N-isopropylacetanilide, pyruvic acid and ammonia were produced from the β-lyase cleavage of the cysteine conjugate of propachlor in equimolar ratios. 4. The apparent K_m values for the cysteine conjugate of propachlor and S-(benzothiazolyl)cysteine were 1.1 and 1.0mM, respectively. 5. Pyridoxal phosphate was required for enzymic activity. Ammonium ion activated enzymic activity, while hydroxylamine completely inhibited the enzyme. Dithiothreitol and bovine serum albumin had no effect on enzymic activity.