   4.1.2.47 | an aliphatic (S)-hydroxynitrile = cyanide + an aliphatic aldehyde or ketone |
proposed reaction mechanism: in free enzyme, the hydroxyl group of Ser80 is hydrogen-bonded to the imidazole nitrogen of His236, which in turn is stabilized by a hydrogen bond with Asp208. If the enzyme encounters a substrate molecule, the proton of Ser80 is rapidly transferred to an imidazole nitrogen of His236. The resulting oxyanion of Ser80 functions as a strong base in a nucleophilic attack of the substrate hydroxyl proton, leading to a negatively charged oxyanion on the substrate. This oxyanion could be stabilized by an oxygen hole formed by amide nitrogen of the backbone of Ser80 and Gly78. Both residues belong to the consensus motif, which is typical for nucleophils located in a catalytic triad. The stabilized oxyanion could further increase the local positive charge on the alpha-C atom of the cyanohydrin, allowing the cyanide group to leave the molecule |
704383 |
