Protects cells against oxidative stress by converting superoxide radicals to hydrogen peroxide (PubMed:9628580). Oxidative stress is involved in various biological dysfunctions and senescence (PubMed:9628580). 2 H(+) + 2 superoxide = H2O2 + O2 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 copper ion per subunit. Binds 1 zinc ion per subunit. Isoform 2 is preferentially expressed in eggs. Isoforms are expressed differently during development, while isoform 2 is preferentially expressed in eggs, isoform 1 is preferentially expressed in the adults. Belongs to the Cu-Zn superoxide dismutase family.