The Biosynthesis of Cyanogenic Glycosides in Higher Plants

An enzyme which catalyzes the transfer of glucose from UDP-glucose to a-hydroxyisobutyronitrile (acetone cyanohydrin) has been isolated from flax seedlings (Zinum usifafissimum L). The product of this reaction was shown to be identical with linamarin, one of the two cyanogenic glucosides produced by the flax plant. The partially purified UDP-glucose-ketone cyanohydrm /3-glucosyltransferase exhibited a high degree of specificity for the two aliphatic side chains of acetone and butanone cyanohydrins as well as for UDP-glucose as the glucose donor. This suggests that its natural function is to catalyze the last step in the biosynthesis of the cyanogenic glucosides linamarin and lotaustralin from the precursor cyanohydrins. In a series of steps resulting in a purification of 120-fold, the glucosyltransferase was separated from the P-glucosidase “linamarase” which is present in the flax plant. No requirements for metal ions or sulfhydryl reagents could be shown for the glucosyl transferase.