Hydroxynitrile lyases of higher plants.

Release of HCN from cyanogenic glycosides is due to the cleavage of the carbohydrate moiety by beta-glucosidases to yield the corresponding alpha-hydroxynitrile, which dissociates spontaneously into HCN and a carbonyl compound, or by action of an alpha-hydroxynitrile lyase (HNL). A short review of the regulation of the catabolism of cyanogenic glycosides during cyanogenesis and germination of cyanogenic plants is given. The major biochemical properties of HNLs purified from various species of higher plants are summarized. Thereafter the phylogenetic relationship, molecular structure and catalytic mechanism of these enzymes are discussed. Finally we give an overview of recent progress in the use of HNLs as biocatalysts for the synthesis of optically active alpha-hydroxynitriles which are important building blocks in the fine chemical and pharmaceutical industries.