Journal Article

Biochemical and molecular characterization of the NAD<sup>+</sup>-dependent isocitrate dehydrogenase from the chemolithotroph <i>Acidithiobacillus thiooxidans</i>

Hiroyuki Inoue, Takashi Tamura, Nagisa Ehara, Akira Nishito, Yumi Nakayama, Makiko Maekawa, Katsumi Imada, Hidehiko Tanaka and Kenji Inagaki

in FEMS Microbiology Letters

Volume 214, issue 1, pages 127-132
Published in print August 2002 |
Published online January 2006 | e-ISSN: 1574-6968 | DOI: http://dx.doi.org/10.1111/j.1574-6968.2002.tb11335.x

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Abstract

An isocitrate dehydrogenase (ICDH) with an unique coenzyme specificity from Acidithiobacillus thiooxidans was purified and characterized, and its gene was cloned. The native enzyme was homodimeric with a subunit of Mr 45 000 and showed a 78-fold preference for NAD+ over NADP+. The cloned ICDH gene (icd) was expressed in an icd-deficient strain of Escherichia coli EB106; the activity was found in the cell extract. The gene encodes a 429-amino acid polypeptide and is located between open reading frames encoding a putative aconitase gene (upstream of icd) and a putative succinyl-CoA synthase β-subunit gene (downstream of icd). A. thiooxidans ICDH showed high sequence similarity to bacterial NADP+-dependent ICDH rather than eukaryotic NAD+-dependent ICDH, but the NAD+-preference of the enzyme was suggested due to residues conserved in the coenzyme binding site of the NAD+-dependent decarboxylating dehydrogenase.

Keywords: Isocitrate dehydrogenase; Decarboxylating dehydrogenase; Coenzyme specificity; Enzyme purification; Acidithiobacillus thiooxidans

Journal Article.  2460 words.  Illustrated.

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