Purification and characterisation of beta-cyanoalanine synthase from cassava tissues

The occurrence of the beta-cyanoalanine pathway for detoxication of cyanide in cassava was examined by studying the activity of beta-cyanoalanine synthase (beta-CAS) [EC.4.4.1.9]: which is the major enzyme involved in the conversion of cyanide to beta-cyanoalanine. beta-CAS was partially purified from cassava leaf, rind and tuber. Its specific activity in the tuber was significantly greater than that in the leaf and rind. The purified enzyme appeared as a single band with M-r of 50 k in SDS-PAGE. On gel filtration over Sephadex G-150, the enzyme was eluted as a single peak with an average M-r of 51 k. beta-CAS from all three tissues had an optimum pH of 9.0 and showed maximum activity at 30 degrees and the K-m (cyanide) was similar. The presence of serine, an alternate substrate for the enzyme did not affect the utilisation of cysteine for the formation of beta-cyanoalanine. (C) 1997 Elsevier Science Ltd.