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°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.