Chemical reagents were designed to cross-link and connect hemoglobin and superoxide dismutase, combining the oxygen transport and superoxide-removal capabilities of the red cell in a dual-function protein. Reaction of 1 with thiol-protected hemoglobin followed by reduction produces cross-linked hemoglobin with a free thiol on the cross-link. Reaction of SOD with 5 produces a cross-linked protein with a maleimide on the cross-link. Addition of the hemoglobin-thiol to the SOD-maleimide produces a protein with the desired dual properties, Hemoglobin's oxygenation cooperativity is lowered as a result of being in the conjugate, while SOD's activity is equal to that of the native protein.