Purification and characterization of 3-isopropylmalate dehydrogenase of acidophilic autotroph Thiobacillus thiooxidans

摘要

3-IsopyImdate dehydrogenase was purified to homogeneity from the acidophilic autotroph Thiobacillus thiooxidans. The native enzyme molecule is a dimer of molecular weight 40,000. The Km value for 3-isopropylmalate was estimated to be 0.13 mM and that for NAD~+ 8.7 mM. The optimum pH and temperature for the activity are 9.0 and 65, respectively. The properties of the enzyme are similar to those of the Thiobacillus ferrooxidans enzymes, except for substrate specificity. T. ferrooxidans 3-isopropylmalate dehydrogenase is able to utilize alkyl-malate as substrate in addition to 34sopropylmalate. However, T. thiooxidans 34sopropylmalate is not able to utilize malate as a substrate.