Purification and some properties of IMP dehydrogenase of Bacillus cereus

IMP dehydrogenase was purified from a crude extract of B. cereus cells. The molecular mass of the purified enzyme was estimated to be 56 kDa by SDS-PAGE and 225 kDa by gel filtration. The optimum pH of the enzyme was about 9.5. The first seven residues at N-terminus of the enzyme was determined to be Met-Trp-Glu-Ser-Lys-Phe-Val. The enzyme showed a significant specificity for inosine nucleotides among 15 purines and pyrimidines tested, but not acted on other purines and pyrimidines including inosine. Among 11 metal ions and 3 enzyme inhibitors tested, A1³⁺ activated the IMP dehydrogenase. The enzyme activity was strongly inhibited by Zn²⁺ and Fe³⁺.