A highly specific D-hydroxyisovalerate dehydrogenase from the enniatin producer Fusarium sambucinum

A highly specific D-hydroxyisovalerate (D-HIV) dehydrogenase, which is a key enzyme in depsipeptide synthesis, was purified to near homogeneity from the enniatin-producing fungus Fusarium sambucinum. The enzyme catalyzes the reversible reaction of 2-ketoisovalerate (2-KIV) to D-HIV. It is strictly dependent on NADPH and exhibits a high substrate specificity with respect to 2-KIV. NADH was not accepted by the enzyme. Km values for 2-KIV and NADPH were found to be 200 and 333 microM, respectively. D-HIV dehydrogenase consists of a single polypeptide chain with a molecular mass of about 53 kDa. Optimum temperature for the reduction of 2-KIV was 35 degrees C and for the oxidation reaction was 45 degrees C. The optimum pH was found to be 7 for the reduction and 8-9 for the oxidation reaction.