Destroys radicals which are normally produced within the cells and which are toxic to biological systems. The plasma superoxide dismutase has phagocytosis-stimulating activity and may play an important role in the biological defenses of the organism. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 copper ion per subunit. Binds 1 zinc ion per subunit. Inhibited by KCN and diethyldithiocarbamate. Monomer. Belongs to the Cu-Zn superoxide dismutase family.