In this work, the electron transfer reactions of horse spleen ferritin at tin-doped indium oxide electrodes were investigated for the first time. Cyclic voltammetry reveals that ferritin adsorbs from phosphate solution into a layer composed of two adsorbed states, the relative packing density of the states depending strongly on ionic strength. Upon reduction, the initial layer reconstructs into a new one with faster electron-transfer kinetics. Reduction of the adsorbed layer in the presence of ethylenediaminetetraacetic acid results in the disappearance of any further voltammetric response indicating that transport of iron from the protein shell had been induced electrochemically.

In this work, the uptake and release of iron by ferritin using direct electrochemical techniques have been investigated for the first time. Adsorption of ferritin from phosphate solution onto tin-doped indium oxide (ITO) at open circuit potential gives about one monolayer of ferritin. The ferritin layer is electroactive and therefore lends itself to electrochemical analysis; cyclic voltammetry was the principal method used in this study. In the presence of EDTA, iron is not removed at open circuit potential. However, when the ITO/ ferritin electrode is subjected to -0.70 V, the anodic branch is no longer present in the current-potential curve, indicating that the reduction of core iron had induced the removal of iron from the protein shell. Adsorbed ferritin, emptied in this fashion, was exposed to ferrous ion at 0.20 V. The ensuing currentpotential curve showed the original peak pattern, suggesting that iron had been reincorporated into the apoferritin shell. An authentic sample of adsorbed apoferritin exposed to ferrous ion, exhibited the same current-potential response as electrochemically emptied ferritin, supporting the conclusion that apoferritin results from the reduction of ITO/ferritin in the presence of an iron chelator. These studies show that ferritin adsorbed at an ITO electrode is a promising venue to study not only ferritin's electrochemistry but also its functions.