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.
- Acidithiobacillus thiooxidans
- Coenzyme specificity
- Decarboxylating dehydrogenase
- Enzyme purification
- Isocitrate dehydrogenase
ASJC Scopus subject areas
- Molecular Biology