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. Homotetramer (By similarity). Directly interacts with ATP7A/MNK; this interaction is copper-dependent and is required for SOD3 activity (By similarity). Belongs to the Cu-Zn superoxide dismutase family.