Analysis of ESR Detectable Cu(II) in Recombinant Human Cu, Zn-SOD

A quantitative analysis of recombinant human Cu, Zn-SOD revealed that the Cu (II) measured by ESR was lower than that of total copper measured by X-ray fluorescence. Several metal-substituted SOD (Cu, E-SOD, Cu, Cu-SOD, Cu, Co-SOD, Cu, VO-SOD and Ag, Cu-SOD) were prepared and compared with recombinant Cu, Zn-SOD. The same phenomena were found in Cu, Cu-SOD, Cu, Co-SOD and Cu, VO-SOD. The amounts of ESR detectable Cu (II) were increased to levels identical with total copper by treatment with 1N HC1 in Cu, Cu-SOD, Cu, Co-SOD and Cu, VO-SOD. In Cu, Zn-SOD ESR detectable Cu (II) was not increased by treatment with 1N HCl, but increased by treatment with a mixture of 10N HNO3 and 60% HClO4 (1:1(V/V)) at 180°C for 24hr. These results suggest that the copper chelated in Cu, Zn-SOD and its metal-substituted SOD exist partially in reduced form which is not detectable by ESR.