Purification and characterization of cystathionine gamma-lyase from Lactobacillus fermentum DT41.

A homo-tetrameric ca. 140-kDa cystathionine gamma-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 alpha,gamma-elimination reaction of L-cystathionine producing L-cysteine, ammonia and alpha-ketobutyrate. The cystathionine gamma-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.