The cyanoalanine synthesis reaction is more efficient than the cysteine synthase activity. Probably involved in detoxification of toxic cyanide produced in plant tissues. hydrogen sulfide + O-acetyl-L-serine = acetate + L-cysteine hydrogen cyanide + L-cysteine = 3-cyano-L-alanine + H(+) + hydrogen sulfide Optimum pH is 8.0-9.0. Homodimer. Expressed in tubers and buds. Detected in leaves. Up-regulated at the protein level by ethylene and 1-Aminocyclopropane-1-carboxylic acid or naphthalene acetic acid treatments. Down-regulated at transcript level by methyl jasmonate. No effect from wounding. Belongs to the cysteine synthase/cystathionine beta-synthase family.