Uptake and Release of Iron by Ferritin Adsorbed at Tin-Doped Indium Oxide Electrodes

Abstract

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.

Electrochemically Induced Iron Release of Adsorbed Horse Spleen Ferritin: Quantitation of Iron Using Long Optical Path Length Thin‐Layer Spectroelectrochemistry

“…It has been shown previously that the theoretical packing density of ferritin on ITO agrees fairly well with the value obtained from the charge under the cathodic peak using the Faraday law, suggesting that one electron is transferred per iron atom [3]. The number of moles of iron atoms reduced was calculated from the charge under the cathodic peak using the same assumption.…”

“…In previous work, the direct electron transfer of ferritin adsorbed on indiumtin oxide (ITO) electrodes had shown that the electrochemical reduction of ferritin is effected without the use of homogeneous reducing agents [2 -6]. Voltammetric data suggested that the reduction of ferritin in the presence of an iron-chelating agent results in the release of iron from the protein shell [3,6]. In order to substantiate this result, the iron released from a layer of adsorbed ferritin should be quantitated by an independent method that measures iron concentration directly.…”

The direct electrochemistry of ferritin compared with the direct electrochemistry of nanoparticulate hydrous ferric oxide

“…This is made possible by the fact that both types of nanoparticle readily adsorb onto tin-doped indium oxide (ITO) electrode surfaces. The adsorption of protein-coated HFO (ferritin) on ITO has been reported previously by Zapiens and coworkers [7,8,9,10]. So far as we are aware, however, the adsorption of bare HFO on ITO is new.…”

Electrochemical Characterization of Horse Spleen Ferritin Covalently Immobilized on Self‐Assembled Monolayer Modified Gold Electrodes

“…The cathodic charge is fairly constant suggesting that covalently immobilized ferritin does not desorb as the ionic strength is varied. In contrast, the packing density of ferritin adsorbed on ITO increased as the ionic strength of the dosing and scanning buffers was increased, then reached a limiting value at 1.2 M ionic strength, indicating that ferritin was immobilized on ITO via an hydrophobic interaction [5].…”

“…The voltammetric signature of covalently immobilized ferritin bears a striking similarity to that of ferritin adsorbed on indium-tin oxide (ITO) electrodes [5]. On ITO, an initial cathodic peak appeared at À 0.62 V (at pH 7.0), followed by a quasireversible couple with a midpoint potential at À 0.28 V. The initial cathodic peak is completely absent in the second cycle, and it was suggested that a conformational or orientation change leads to the diminished electroactivity.…”