Enzymatic Formation of β-Cyanoalanine from Cyanide

IN 1963 Blumenthal-Goldschmidt et al.¹ demonstrated the incorporation of ¹⁴C-labelled hydrogen cyanide into asparagine by seedlings of a number of plant species. They showed that the label from H¹⁴CN almost exclusively entered the amide carbon of asparagine and obtained preliminary evidence that the other three carbon atoms might be provided by serine or a closely related metabolite. These findings have been confirmed and extended by Tschiersch^2,3, Ressler et al.^4,5 and by Fowden and Bell⁶. The available evidence suggests that HCN reacts with serine to form β-cyanoalanine which then, depending on the plant species used, can either be hydrolysed to asparagine or can be converted into a peptide, γ-glutamyl-β-cyanoalanine. The two latter reactions have been demonstrated in extracts of seedlings⁶, but enzymatic evidence for the first reactions has so far not been reported.