Cyanogenesis in Cassava¹
The Role of Hydroxynitrile Lyase in Root Cyanide Production

Wanda L.B. White, Diana I. Arias-Garzon, Jennifer M. McMahon, and Richard T. Sayre^*

Department of Plant Biology, 1735 Neil Avenue (W.L.B.W., D. I.A.-G., J.M.M.), and Departments of Biochemistry and Plant Biology, 2021 Coffey Road, Ohio State University, Columbus, Ohio 43210 (R.T.S.)

In the cyanogenic crop cassava (Manihot esculenta, Crantz), the final step in cyanide production is the conversion of acetone cyanohydrin, the deglycosylation product of linamarin, to cyanide plus acetone. This process occurs spontaneously at pH greater than 5.0 or enzymatically and is catalyzed by hydroxynitrile lyase (HNL). Recently, it has been demonstrated that acetone cyanohydrin is present in poorly processed cassava root food products. Since it has generally been assumed that HNL is present in all cassava tissues, we reinvestigated the enzymatic properties and tissue-specific distribution of HNL in cassava. We report the development of a rapid two-step purification protocol for cassava HNL, which yields an enzyme that is catalytically more efficient than previously reported (Hughes, J., Carvalho, F., and Hughes, M. [1994] Arch Biochem Biophys 311: 496-502). Analyses of the distribution of HNL activity and protein indicate that the accumulation of acetone cyanohydrin in roots is due to the absence of HNL, not to inhibition of the enzyme. Furthermore, the absence of HNL in roots and stems is associated with very low steady-state HNL transcript levels. It is proposed that the lack of HNL in cassava roots accounts for the high acetone cyanohydrin levels in poorly processed cassava food products.

Plant Physiol. (1998) 116: 1219-1225
Copyright Clearance Center:   0032-0889/98/116/1219/07
© 1998 American Society of Plant Physiologists

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