Primarily catalyzes the cleavage of cystathionine to homocysteine, pyruvate and ammonia during methionine biosynthesis (PubMed:7049234). Also exhibits cysteine desulfhydrase activity, producing sulfide from cysteine (PubMed:12883870). In addition, under certain growth conditions, exhibits significant alanine racemase coactivity (PubMed:21193606). H2O + L,L-cystathionine = L-homocysteine + NH4(+) + pyruvate H2O + L-cysteine = H(+) + hydrogen sulfide + NH4(+) + pyruvate an S-substituted L-cysteine + H2O = a thiol + NH4(+) + pyruvate L-cysteine inhibits cystathionine beta-lyase activity competitively (PubMed:7049234). Inhibited by aminoethoxyvinylglycine (AVG) (PubMed:9376370). Optimum pH is 8.0-9.0. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homocysteine from L-cystathionine: step 1/1. Homotetramer; dimer of dimers. Disruption of the gene increases the amounts of L-cysteine and L-cystine produced after 72 hours of cultivation. Belongs to the trans-sulfuration enzymes family.