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A Novel Deaminase Involved in Chloronitrobenzene and Nitrobenzene Degradation with Comamonas sp. Strain CNB-1

State Key Laboratory of Microbial Resource, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100080, People's Republic of China,¹ Chinese National Human Genome Center at Shanghai, Shanghai, 200031, People's Republic of China²

Received 18 November 2006/ Accepted 29 January 2007

Comamonas sp. strain CNB-1 degrades nitrobenzene and chloronitrobenzene via the intermediates 2-aminomuconate and 2-amino-5-chloromuconate, respectively. Deamination of these two compounds results in the release of ammonia, which is used as a source of nitrogen for bacterial growth. In this study, a novel deaminase was purified from Comamonas strain CNB-1, and the gene (cnbZ) encoding this enzyme was cloned. The N-terminal sequence and peptide fingerprints of this deaminase were determined, and BLAST searches revealed no match with significant similarity to any functionally characterized proteins. The purified deaminase is a monomer (30 kDa), and its V_max values for 2-aminomuconate and 2-amino-5-chloromuconate were 147 µmol·min^–1·mg^–1 and 196 µmol·min^–1·mg^–1, respectively. Its catalytic products from 2-aminomuconate and 2-amino-5-chloromuconate were 2-hydroxymuconate and 2-hydroxy-5-chloromuconate, respectively, which are different from those previously reported for the deaminases of Pseudomonas species. In the catalytic mechanism proposed, the -carbon and nitrogen atoms (of both 2-aminomuconate and 2-amino-5-chloromuconate) were simultaneously attacked by a hydroxyl group and a proton, respectively. Homologs of cnbZ were identified in the genomes of Bradyrhizobium japonicum, Rhodopseudomonas palustris, and Roseiflexus sp. strain RS-1; these genes were previously annotated as encoding hypothetical proteins of unknown function. It is concluded that CnbZ represents a novel enzyme that deaminates xenobiotic compounds and/or -amino acids.

Published ahead of print on 26 January 2007.

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