Cu/Zn containing superoxide dismutase (SOD) belongs to the family of related enzymes which have the same catalytic function but are structurally different. SOD catalyzes the dismutation of the superoxide radical O2-to O2 and H2O2 which in turn is metabolized to H2O and O2 by catalase and glutathione peroxidase (1, 2). The SOD family is classified into subfamilies on the basis of their metal cofactors which could be either a dinuclear Cu/Zn or mononuclear Fe, Mn or Ni. The Fe-and Mn-SODs have identical metal chelating residues at the active site and share substantial sequence and tertiary homology, whereas the other SODs are structurally unrelated. The Cu/Zn-SOD is found in the cytosol of eukaryotes, in chloroplasts and in the periplasm of some prokaryotes. The eukaryotic, Cu/Zn-SODs usually consists of two identical subunits of 16kD each that are linked by two cysteines forming an intrasubunit disulfide bridge and each subunit contains a metal cluster at the active site. The Cu/Zn-SOD is believed to play a major role in antioxidant defence mechanisms (3,5). Fe-SOD is present in both aerobic and anaerobic bacteria, Archaea and plants whereas Mn-SOD is present in bacteria, Archaea, mitochondria and chloroplasts. In animals, Mn-SOD is present predominately in the mitochondria as a tetramer of 80kD (3,4). SODs are involved in maintaining the cell integrity and protecting the functionality of the single cell components against the damages by oxidative stress (5).