Superoxide dismutase from the silkworm, Bombyx mori: sequence, distribution, and overexpression

Superoxide dismutase (SOD) is an enzyme facilitating the removal of superoxide anions from living organisms. This study focused on SOD from the silkworm, Bombyx mori (bmSOD). cDNA encoding bmSOD was amplified by reverse transcriptase-polymerase chain reaction. The deduced amino acid sequence of bmSOD indicated that the residues forming the Cu/Zn binding site are conserved and that the sequence is in 60% identity to that of the Drosophila melanogaster. B. mori SOD was also close to the D. melanogaster SOD in a phylogenetic tree. The bmSOD mRNA and the enzyme activity were widely distributed in diverse tissues. bmSOD functionally overexpressed in Escherichia coli in a soluble form was purified, and its stability was examined. bmSOD at 4 degrees C retained almost all of its original activity after incubation at pH 4-11 for 24 h. Incubation (pH 7) for 30 min at temperatures below 40 degrees C also affected activity insignificantly.