Nitrile [R-CN] and its isomer, isonitle [R-NC] are very toxic compounds. Although microbial degradation of nitriles have well been clarified at the protein and gene levels, information is quite limited on isonitrile metabolism. Through enrichment culture using isonitrile as the sole carbon and nitrogen sources, we obtained isonitrile-degrading microorganisms: Pseudomonas putida and Arthrobacter pascens. We identified their degradation products and clarified the metabolic pathway. We discovered two new enzymes. Isonitrile hydratase (InhA) catalyzes hydration of isonitrile to N-substituted formamide [R-NH-CH(=O)], followed by degradation to amine [R-NH2] and formate [H-COOH] by N-substituted formamide deformylase (NfdA). New EC numbers (EC 4.2.1.103 and EC 3.5.1.91) have been given to InhA and NhfA, respectively, and they have been approved as new enzymes by NC-IUBMB (International Union of Biochemistry and Molecular Biology). We cloned their enzyme genes and found weak amino acid similarities between each enzyme and other enzymes.
During the studies on culture conditions in A. pascens, we recently found that isonitrile-degrading enzyme is an inducible enzyme. Although this Arthrobacter enzyme (named InhB) and the Pseudomonas enzyme (InhA) were inhibited by sulfhydryl reagents, both of the enzymes have been found to be biochemically and imunologically different from each other, demonstrating that InhB is a new isonitrile hydratase. We clarified the active amino acid residues of the both isonitrile hydratases and their catalytic mechanisms. In addition, production of useful compounds has been investigated using NfdA.