Probably involved in the detoxification of cyanide that arises from ethylene biosynthesis in ripening fruits. Has only background level of in vitro cysteine synthase activity. hydrogen cyanide + L-cysteine = 3-cyano-L-alanine + H(+) + hydrogen sulfide Expressed in leaves, flowers and fruits. Up-regulated during the ripening process of fruits. Up-regulated by ethylene treatment and wounding. Belongs to the cysteine synthase/cystathionine beta-synthase family.