Abstract:A 977 bp cDNA containing an open reading frame encoding 224 amino acid residues of manganese superoxide dismutase was cloned from zebrafish (zMn–SOD). The deduced amino acid sequence showed high identity with the sequences of Mn–SODs from human (85.1%) to nematode (61.6%). The 3-D structure model was superimposed on the relative domains of human Mn–SOD with the root mean square (rms) deviation of 0.0919 Å. The recombinant mature zMn–SOD with enzyme activity was purified using His-tag technique. The half-life of the enzyme is approximately 48 min and its thermal inactivation rate constant kd is 0.0154 min−1at 70 °C. The enzyme was active under a broad pH (2.2–11.2) and in the presence of up to 4% SDS. Real-time RT-PCR assay was used to detect the zMn–SOD mRNA expression during the developmental stages following a challenge with paraquat. A high level expression of Mn–SOD mRNA was detected at the cleavage stage, but decreased significantly under paraquat treatment. The results indicated that Mn–SOD plays an important role during embryonic development.