. "Catalysis of the reaction: L-serine + L-homocysteine = cystathionine + H2O." . . "cystathionine beta-synthase activity" . "beta-thionase activity" . "L-serine hydro-lyase (adding homocysteine)" . "methylcysteine synthase activity" . "serine sulfhydrase activity" . "serine sulfhydrylase activity" . "L-serine hydro-lyase (adding homocysteine, L-cystathionine-forming)" . . .