title: Purification and characterization of 3-isopropylmalate dehydrogenase from Thiobacillus thiooxidans.
abstract: 3-Isopropylmalate dehydrogenase was purified to homogeneity from the acidophilic autotroph Thiobacillus thiooxidans. The native enzyme was a dimer of molecular weight 40,000. The apparent K(m) values for 3-isopropylmalate and NAD+ were estimated to be 0.13 mM and 8.7 mM, respectively. The optimum pH for activity was 9.0 and the optimum temperature was 65 degrees C. The properties of the enzyme were similar to those of the Thiobacillus ferrooxidans enzyme, expect for substrate specificity. T. thiooxidans 3-isopropylmalate dehydrogenase could not utilize malate as a substrate.
authors.affiliation: Department of Bioresources Chemistry, Faculty of Agriculture, Okayama University, Okayama 700-8530, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kawaguchi
authors.forename: K
authors.initials: K
authors.lastname: Inagaki
authors.forename: H
authors.initials: H
authors.lastname: Matsunami
authors.forename: Y
authors.initials: Y
authors.lastname: Nakayama
authors.forename: T
authors.initials: T
authors.lastname: Tano
authors.forename: H
authors.initials: H
authors.lastname: Tanaka