Molecular and biochemical characterization of manganese-containing superoxide dismutase from the silkworm, Bombyx mori

Superoxide dismutase (SOD) is responsible for the removal of superoxide anion from living organisms. In this study, cDNA encoding the manganese-containing SOD (MnSOD) from the silkworm, Bombyx mori, was isolated by reverse transcriptase-polymerase chain reaction and sequenced. The deduced amino acid sequence of the MnSOD revealed 62% identity to that of the Drosophila melanogaster; both were close to each other in a phylogenetic tree. The MnSOD was overproduced in Escherichia coli and purified. The internal structure of the recombinant MnSOD was confirmed by peptide mass fingerprinting method. The recombinant MnSOD facilitating the reduction reaction of superoxide anion retained 75% of its original activity after incubation at pH 4-11 for 24 h at 4 °C. Its activity was never affected by incubation at pH 7 for 30 min below 50 °C.