A pyridoxal-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing L-homocysteine and an unstable enamine product that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form pyruvate and ammonia. The latter reaction, which can occur spontaneously, can also be catalysed by EC 126.96.36.199, 2-iminobutanoate/2-iminopropanoate deaminase. The enzyme from some sources also acts on L-cystine, forming pyruvate, ammonia and cysteine persulfide, and a number of related compounds. Possibly identical, in yeast, with EC 188.8.131.52 S-alkylcysteine lyase.