Selective hydrolysis of the nitrile group of cis-dihydrodiols from aromatic nitriles

Several nitrilases were screened for the hydrolysis of the nitrile group of cis-1,2-dihydroxy-3-cyanocyclohexa-3,5-diene and trans-3-[(5S,6R)-5,6-dihydroxycyclohexa-1,3-dienyl]-acrylonitrile to the corresponding acids. Nitrilase from Rhodococcus sp. was able to convert both compounds with the activity of 0.3 mU/mg protein and 0.05 mU/mg protein, respectively. Nitrilase AtNIT1 from Arabidopsis thaliana converted only the latter but with a higher initial specific activity of 1.7 mU/mg protein. Biotransformation of trans-3-[(5S,6R)-5,6-dihydroxycyclohexa-1,3-dienyl]-acrylonitrile was performed with AtNIT1 in the form of isolated enzyme and immobilized enzyme, and with recombinant cells containing AtNIT1. Biotransformations with isolated AtNIT1 resulted in 116 mg of product in 10.6 h with a yield of 77%. Forty-three percent of the enzymatic activity could be recovered after the biotransformation. Immobilization of AtNIT1 saturated with 3-phenylpropionitrile resulted in 3.5% of the free enzyme activity. Biotransformations with Escherischia coli JM101 (pQE10-AtNIT1) in shake-flasks produced 243 mg of product in 23 h with a yield of 48%. Maximum and average specific activities of 0.5 U/g cell dry weight and 0.17 U/g cell dry weight were achieved, respectively.