HYDROXYNITRILE LYASES OF HIGHER-PLANTS

Release of HCN from cyanogenic glycosides is due to the cleavage of th e carbohydrate moiety by beta-glucosidases to yield the corresponding alpha-hydroxynitrile, which dissociates spontaneously into HCN and a c arbonyl compound, or by action of an alpha-hydroxynitrile lyase (HNL). A short review of the regulation of the catabolism of cyanogenic glyc osides during cyanogenesis and germination of cyanogenic plants is giv en. The major biochemical properties of HNLs purified from various spe cies of higher plants are summarized. Thereafter the phylogenetic rela tionship, 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 alph a-hydroxynitriles which are important building blocks in the fine chem ical and pharmaceutical industries.