Purification and characterization of cystathionine γ‐lyase from Lactobacillus fermentum DT41

A homo‐tetrameric ca. 140‐kDa cystathionine γ‐lyase was purified to homogeneity from Lactobacillus fermentum DT41 by four chromatographic steps. This was the first enzyme responsible for amino acid catabolism purified from lactobacilli. The activity is pyridoxal‐5′‐phosphate dependent and the enzyme catalyzes the α,γ‐elimination reaction of l ‐cystathionine producing l ‐cysteine, ammonia and α‐ketobutyrate. The cystathionine γ‐lyase produced a free thiol group, a keto acid component and ammonia from several amino acids, including l ‐cysteine and methionine, and amino acid derivatives. l ‐Cystine was the best substrate. The enzyme was stable in the conditions of cheese ripening and may contribute to the biosynthesis of sulfur‐containing compounds.