The redox interaction between O2 − and ferritin cannot solely be regarded as a Fe(II) release reaction. We demonstrate that native copper bound to horse spleen ferritin and apoferritin, stimulated the decay of O2 − in a catalytic reaction. Copper was determined by atomic absorption spectrophotometry. Decay of O2 − was monitored spectrophotometrically as the decrease in (A 250-A 360) at pH 9.5. The catalytic effect was linearly related to the copper content of the protein. Ferritin copper was less efficient than equimolar CuCl2, and iron-poor ferritin was more efficient than iron-rich ferritin. The results support a direct antioxidant function of ferritin.
