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J. Bacteriol. doi:10.1128/JB.01762-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

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, P. R. China; Chinese National Human Genome Center at Shanghai, 200031, P. R. China

^* To whom correspondence should be addressed. Email: liusj{at}sun.im.ac.cn.

	Abstract

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 that 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. RS-1; these genes were previously annotated as hypothetical proteins of unknown function. It is concluded that CnbZ represents a novel enzyme that deaminates xenobiotic compounds and/or -amino acids.

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