Rhodococcus rhodochrous NCIMB 11216 grows on propionitrile or benzonitrile as the sole source of carbon and nitrogen. The possibility that different nitrile-hydrolyzing enzymes were produced under these two growth conditions was investigated. Nitrilase activity in whole cell suspensions from either bacteria grown on propionitrile or benzonitrile were capable of biotransforming a wide range of nitriles. The propionitrile-induced nitrile degrading activity hydrolyzed 3-cyanobenzoate and both the nitrile groups in 1,3-dicyanobenzoate. In contrast, the benzonitrile-induced activity hydrolyzed only one of the nitrile groups in 1,3-dicyanobenzoate, but did not affect 3-cyanobenzoate. Both nitrilases biotransformed alpha-cyano-o-tolunitrile to produce 2-cyanophenylacetic acid. The nitrilases were purified by fast protein liquid chromatography and the iv-terminus of each enzyme sequenced. SDS-PAGE analysis identified a subunit molecular weight of 45.8 kDa for each nitrilase. The N-terminal sequences showed significant similarity with other sequenced nitrilases and with the exception of a single amino acid were identical with each other. Both nitrilases had temperature and pH optima of 30 degrees C and 8.0, respectively. The propionitrile-induced nitrilase had a K-m for benzonitrile of 20.7 mM and a V-max of 12.4 mu mol min(-1) mg(-1) protein whereas the benzonitrile-induced nitrilase had a K-m for benzonitrile of 8.83 mM and a V-max of 0.57 mu mol min(-1) mg(-1) protein.