Catalyzes the transformation of cystathionine into homocysteine (PubMed:19035565). Can also catalyze, at low levels, the conversion of cystathionine into methionine and the conversion of methionine into methanethiol (PubMed:19035565). H2O + L,L-cystathionine = L-homocysteine + NH4(+) + pyruvate an S-substituted L-cysteine + H2O = a thiol + NH4(+) + pyruvate Cystathionine beta-lyase activity is inhibited by sweat components such as glycine, serine and ammonium sulfate. Inhibited by cystathionine at a concentration higher than 6 mM. Optimum pH is 8.5. Optimum temperature is 37 degrees Celsius. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homocysteine from L-cystathionine: step 1/1. Homotetramer. Belongs to the trans-sulfuration enzymes family.