Asymmetric hydrolysis of α-aminonitriles to optically active amino acids by a nitrilase of Rhodococcus rhodochrous PA-34

Rhodococcus rhodochrous PA-34 isolated from soil as a propionitrile-utilizing microorganism, hydrolysed several α-aminonitriles to optically active amino acids. The hydrolysis of α-aminonitriles was found to be catalysed by a nitrilase. The characteristics of the purified enzyme revealed that this is a new nitrilase as it has a molecular mass of 45 kDa and acts as a monomer. The optimum pH and temperature for the activity of the purified enzyme were 7.5 and 35° C, respectively. Thiol-specific reagents caused inhibition whereas chelators did not significantly alter the activity of this enzyme. The amino acids produced were of L-form, except for alanine. In the case of leucine production from α-aminoisocapronitrile, the enantiomeric ratio of L-leucine to D-leucine was about 60.