Protect the extracellular space from toxic effect of reactive oxygen intermediates by converting superoxide radicals into hydrogen peroxide and oxygen. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 copper ion per subunit. Binds 1 zinc ion per subunit. Homodimer (PubMed:8643556). Interacts with ATP7A; this interaction is copper-dependent and is required for SOD3 activity. Belongs to the Cu-Zn superoxide dismutase family.