Decay of superoxide catalyzed by ferritin.

Ferritin iron can be reduced by O2.-, released, and form a Fe(II)-chelator complex. However, the thermodynamic influence of the chelator may disturb the reaction balance. We therefore excluded the chelator and measured instead the effect of ferritin on the decay of O.2-, monitored by direct spectrophotometry at pH 9.5. Ferritin, but not apoferritin, accelerated the decay of O.2-. Ferritin iron was apparently the responsible agent. The effect of ferritin was maintained after several bursts of O.2-, and the ratio degraded O.2-/released Fe(II) greatly exceeded one, consistent with a catalytic reaction.