Superoxide dismutase activity in the giant hemoglobin of the earthworm, Lumbricus terrestris

The giant hemoglobin, which occurs in free solution in the blood of earthworms, contains copper and zinc and exhibits superoxide dismutase activity as assessed by competition assays using cytochrome c or nitroblue tetrazolium. On a molar basis, the activity of this hemoglobin was approximately 10% that of the mammalian copper, zinc superoxide dismutase. The dodecamer, which contains the globin chains but lacks the linker subunits, had very little activity when compared to the complete native molecule. This suggests that the superoxide dismutase activity resides in one of the linker subunits. This is the first report of a superoxide dismutase bound to a respiratory pigment.