Superoxide dismutase (SOD) catalyzes the removal of the O2- free radical. The enzyme protects oxygen-metabolizing cells against harmful effects of superoxide free-radicals. Superoxide dismutase is inactivated by H2O2. It consists of two subunits of identical molecular weight joined by a disulfide bond. The molecular weight is 32,500 daltons, and there are two Cu(II) and two Zn(II) atoms per molecule. The isoelectric point of the enzyme is 4.95.