Erythrocuprein (Cu2Zn2 superoxide dismutase) is the major copper protein of the red blood cell.

The copper balance in the red blood cell deserved special attention as the exact amount of copper being bound in erythrocuprein (Cu2Zn2 superoxide dismutase) is poorly understood. An improved aqueous isolation of erythrocuprein revealed that essentially all erythrocyte copper is found in this protein. This fact is supported by both superoxide dismutase activity measurements of the haemolysate and EPR-quantification studies throughout the course of the isolation.