Copper activation of superoxide dismutase in rat erythrocytes

Several lines of evidence suggested that copper can activate a preexisting pool of superoxide dismutase (SOD) apoprotein in erythrocytes from copper-deficient rats. First, feeding adequate copper to copper-deficient rats raised initially low erythrocyte SOD activities to normal values in under one-third the time needed to replace the entire red cell population. Moreover, copper injection (1 mg Cu/kg, sc) doubled erythrocyte SOD activity levels in 16 h. Since protein synthesis is restricted in mature erythrocytes, these results imply that copper activated apoSOD in vivo. Furthermore, injected copper raised SOD activity contents of both young and old erythrocytes. Neither dietary copper status nor copper injection influenced red cell SOD immunoreactive protein levels. In contrast, copper injection increased the amount of copper associated with the SOD activity peak region resulting from gel filtration of hemoglobin-free erythrocyte proteins on Sephadex G-75. Copper ions (3 microM) elevated SOD activity levels in vitro by 63% in 4 h in intact red cells from copper-deficient rats. No activation took place in lysed red cells from the same rats or in intact cells from copper-adequate rats. These results all suggest that copper can activate SOD apoprotein in erythrocytes by a specific, saturable process.