Characterization of Copper/Zinc Superoxide Dismutase Activity on Phascolosoma esculenta (Sipuncula: Phascolosomatidea) and Its Protection from Oxidative Stress Induced by Cadmium.

, an economically important species inhabiting the high tide areas of the intertidal zone, is particularly sensitive to water pollution. Considering its potential as a bioindicator, studies on the ecotoxicology of are imperative. The toxic effects of cadmium (Cd) were analyzed by exposing to different concentrations of Cd (6, 24, 96 mg/L). In this study, the changes in the antioxidative indexes of total superoxide dismutase (T-SOD), glutathione s-transferase (GST), reduced glutathione (GSH), and microscale malondialdehyde (MDA) were recorded. Copper/zinc superoxide dismutase (Cu/Zn SOD) is one of the most important free radical scavenging members. To reveal the antioxidative function of an important member of the antioxidative system, designated , was cloned and analyzed. Phylogenic analysis revealed that was located in the invertebrate evolutionary branch of intracellular Cu/Zn SOD (icCu/Zn SOD). The quantitative real-time polymerase chain reaction results showed that messenger ribonucleic acid was widely expressed in all tissues examined. The highest expression levels in coelomic fluid after Cd exposure indicated its function in the stress response. Using a prokaryotic expression system, we obtained a recombinant protein, which enhanced the heavy metal tolerance of . In vivo assays also confirmed that the recombinant protein had an antioxidative and free radical scavenging ability. A Cd toxicity experiment, in which purified protein was injected into the body cavities of , showed that the reactive oxygen species content in the coelomic fluid of the experimental group was significantly lower compared with the control group. These results suggest that played a role in Cd detoxification by chelating heavy metal ions and scavenging reactive oxygen free radicals, and that could be used as a bioindicator to evaluate heavy metal pollution.