Relationship between the ligand structure of copper and the stability of superoxide dismutase.

Abstract

The ligand structure of chelated copper in recombinant human Cu(2)Zn(2)SOD (r-hSOD) and its metal-substituted SODs was examined. In r-hSOD the configuration of the copper binding site was axially symmetrical and that of metal-substituted SODs had a tendency to change towards a tetrahedral type compared with r-hSOD except for Cu(2)(VO)(2)SOD. Cu(2)(VO)(2)SOD was not tetrahedral and in this case the ligand atom of copper was inclined to convert from nitrogen towards oxygen. In Cu(2)E(2)SOD, Ag(2)Cu(2)SOD, and Cu(2)(VO)(2)SOD the specific activities were lower but in CU(2)Cu(2)SOD and Cu(2)Co(2)SOD they were nearly identical with that of r-hSOD. These results suggested the ligand structure of chelated copper was not related to the specific activity of SOD. However, these SODs were less stable than r-hSOD against heat treatment and denaturing reagent. Further they were less stable against attack by an inactivator (hydrogen peroxide) except for Cu(2)(VO)(2)SOD. In this case the decreased stability of these SODs was associated with the change of the ligand structure of copper from that of r-hSOD. These results suggested that the presence of zinc contributed highly to the stable formation of the ligand structure of copper and the enzymatic stability.