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2,3-Dihydroxybenzoic acid decarboxylase from Aspergillus niger A novel decarboxylase

Santha, Ramakrishnan and Savithri, Handanahal S and Rao, Appaji N and Vaidyanathan, Chelakara S (1995) 2,3-Dihydroxybenzoic acid decarboxylase from Aspergillus niger A novel decarboxylase. In: European Journal Of Biochemistry, 230 (1). pp. 104-110.

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2,3-Dihydroxybenzoic acid decarboxylase, the last enzyme in the fungal metabolism of indole to catechol, catalyzes the non-oxidative decarboxylation of 2,3-dihydroxybenzoic acid to catechol. Unlike most other decarboxylases, this enzyme does not require a cofactor, underlining the importance of active-site residues in the reaction mechanism. Earlier studies from this laboratory [Kamath, A. V., Appaji Rao, N. & Vaidyanathan, C. S. (1989) Biochem. Biophys. Res, Commun. 165, 20-26], have shown that the sulfhydryl agent N-ethylmaleimide (MalNEt) inactivated the enzyme by modifying a single class of cysteine residues and that this inactivation was prevented in the presence of salicylate, a substrate analogue. in the present study, this essential cysteine residue has been identified by specific labelling with [C-14]-MalNEt using the differential labelling technique. The stoichiometry of incorporation of [C-14]MalNNEt was approximately one/subunit of the homotetrameric protein. The peptide bearing this reactive cysteine residue was isolated by tryptic digestion of the differentially labelled enzyme and subsequent reverse-phase chromatography of the peptide mixture. The sequence of the major radioactive peptide that was identified to be the active-site peptide, was LLGLAETCK. A search for sequences similar to this active-site peptide indicated that this sequence was probably unique to the decarboxylase under study. A partial primary structure map constructed from the sequences of peptides derived from enzymic cleavage of the protein using endoproteinase Glu-C and trypsin did not share any significant sequence similarity with sequences reported in the database, again suggesting the uniqueness of the enzyme. This is the first report on the active-site peptide and the partial primary structure of a non-oxidative decarboxylase catalyzing the removal of a carboxyl group from an aromatic nucleus.

Item Type: Journal Article
Publication: European Journal Of Biochemistry
Publisher: Springer
Additional Information: Copyright of this article belongs to springer
Keywords: Biochemistry & Molecular Biology;Decarboxylase;Nonoxidative Decarboxylation;Aromatic Acids;Active-Site Cysteine;Primary Structure;2,3-Dihydroxybenzoic Acid
Department/Centre: Division of Biological Sciences > Biochemistry
Date Deposited: 11 Feb 2009 06:28
Last Modified: 19 Sep 2010 05:25
URI: http://eprints.iisc.ac.in/id/eprint/18848

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