Catalyzes the alpha,gamma-elimination of L-methionine to produce methanethiol, 2-oxobutanoate and ammonia. Is probably involved in L-methionine catabolism. Is also able to catalyze the alpha,gamma-elimination of L-homocysteine, and, to a lesser extent, the alpha,beta-elimination of L-cysteine. H2O + L-methionine = 2-oxobutanoate + methanethiol + NH4(+) H2O + L-homocysteine = 2-oxobutanoate + H(+) + hydrogen sulfide + NH4(+) H2O + L-cysteine = H(+) + hydrogen sulfide + NH4(+) + pyruvate kcat is 2.90 sec(-1) for the alpha,gamma-elimination of L-methionine. kcat is 1.67 sec(-1) for the alpha,gamma-elimination of L-homocysteine. kcat is 0.03 sec(-1) for the alpha,beta-elimination of L-cysteine. Homotetramer; dimer of active dimers. Belongs to the trans-sulfuration enzymes family.