Purification and characterization of S-alkylcysteine alpha,beta-lyase from Pseudomonas putida

S-Alkylcysteine alpha,beta-lyase [EC 4.4.1.6] was purified to more than 90% homogeneity from the cell extract of Pseudomonas putida ICR 3640. The enzyme has a molecular weight of about 195,000, and is composed of six subunits identical in molecular weight (37,000). Pyridoxal 5'-phosphate is required as a cofactor. The enzyme catalyzes the alpha,beta-elimination of S-methyl-L-cysteine and its analogs such as S-ethyl-L-cysteine, L-djenkolate, Se-methyl-DL-selenocysteine, and O-methyl-L-serine. However, S-methyl-D-cysteine, L-methionine, and L-norvaline were inert. The enzyme catalyzes also the beta-replacement reaction of the thiomethyl group of S-methyl-L-cysteine with various thiols to yield the corresponding S-substituted cysteines. In addition to S-methyl-L-cysteine, Se-methyl-DL-selenocysteine and O-methyl-L-serine also serve as substrates in the beta-replacement reaction.