[1][2][3][4][5][6][7][8][9][10] This enzyme catalyses the interconversion between cyanohydrins and the carbonyl compounds derived from the cyanohydrin with free cyanide, as in the following two chemical reactions: In nature, the liberation of cyanide serves as a defense mechanism against herbivores and microbial attack in plants.
In contrast to esterases, serine proteases, lipases and other enzymes in this family, the nucleophile in hydroxynitrile lyases functions as a proton acceptor.
[14] Lys236 helps to orient the substrate while Thr11 serves to block the oxyanion hole that would convert the enzyme into an esterase.
[15] Commonly studied (S)-selective hydroxynitrile lyases include MeHNL from Manihot esculenta and HbHNL from Hevea brasiliensis.
In addition to cyanohydrin cleavage, HNLs have been found to catalyze the nitroaldol reaction at low levels.