Monday, August 2, 2010
Pacific Concourse (Hyatt Regency San Francisco)
We discovered an intriguing hemoprotein [aliphatic aldoxime dehydratase (OxdA)] that catalyzes the dehydration of aliphatic aldoximes [R–CH=N–OH] to the corresponding nitriles [R–C≡N] in the industrial Pseudomonas chlororaphis B23 strain(1). It has been approved as a new enzyme by NC-IUBMB: EC 4.99.1.5. The enzymatic reaction from aldoxime to nitrile is not only academically interesting but also expected to be applicable to the practical production of nitriles, because it is performed under mild conditions in contrast with the chemical dehydration of aldoxime under harsh conditions. The OxdA reaction is involving the direct binding of a substrate to the heme iron without other exogenous compounds, and therefore it is strongly attracting the attention of not only biochemists but also biophysicists. We have been identified the proximal and distal histidine residues involved in carbon-nitrogen triple bond synthesis by aldoxime dehydratase(2) and proposed the unique reaction mechanism(3).
In order to investigate the reaction mechanism of aldoxime dehydratase in detail, we have attempted to analyse other aldoxime dehydratase which is derived from other species (in Pseudomonas genus). First, we constructed an Escherichia coli transformant expressing OxdA homologue, purified the enzyme and characterized the enzymological properties (substrate specificity, heme content, and so on). Furthermore, we constructed and characterized two OxdA mutants of histidines conserved in the aldoxime dehydratase superfamily. Based on the results, we clarified the heme environment of the OxdA homologue.
1) JBC, 277, 45860 (2002); 2) JBC, 278, 29600 (2003); 3) PNAS, 103, 564 (2006)