Hydroxynitrile lyases from almond and sorghum as biocatalysts

Hydroxynitrile lyases from sweet almond (E.C. 4.1.2.10) and from sorghum bicolor (E.C. 4.1.2.11) have been purified to homogeneity by ion‐exchange chromatography. These enzymes catalyse the decomposition of α‐hydroxynitriles to aldehydes and hydrocyanic acid (HCN) and show great promise for synthetic applications in the reverse reaction: the stereospecific addition of HCN to aldehydes to form enantio‐pure α‐hydroxynitriles. Physical and kinetic characteristics of the two dominating isoenzymes in each source were compared and revealed appreciable species‐specific differences. The differences in substrate specificity between iso forms within one species, were, however, found to be small. The native molecular weight for the sorghum lyase was found to be 95 kDa. This is in contrast with an earlier reported value of 180 kDa. From the kinetic parameters Km and Kmax, a specificity constant was calculated, which can be used to predict the potential application of oxynitrilase as a biocatalyst for specific synthetic purposes.