Electrochemical behavior of ferritin at the polarized water|1,2-dichloroethane interface

https://doi.org/10.1016/j.elecom.2018.04.010Get rights and content

Highlights

  • Cationic ferritin subunits responded in the positively polarized interface.

  • Ferritin was transferred across the interface accompanied by adsorption processes.

  • Ion transfer of the organic electrolyte anion was facilitated by the positively charged ferritin.

  • Ferritin formed a film at the interface depending on the concentration.

Abstract

The electrochemical behavior of ferritin at the polarized water|1,2-dichloroethane (DCE) interface was studied, mainly under acidic conditions. No obvious voltammetric responses were observed under neutral and alkaline conditions where ferritin formed an uncharged nanocage structure. On the other hand, large electrochemical responses were obtained in the positive potential region under acidic conditions where ferritin was disassembled into positively charged subunits. These responses varied slightly with the concentration of the supporting electrolyte in the organic phase and changed drastically with the concentration of ferritin and under repetitive sweeps. In addition, depending on the applied potential and the concentration of ferritin, a white film was formed at the interface. This electrochemical behavior could be attributed to ion transfer and the adsorption/desorption of positively charged ferritin subunits with the interfacial activity accompanied by the facilitated ion transfer of the organic supporting electrolyte anion.

Introduction

Ferritin is a well-known iron storage and detoxification protein, which is ubiquitous in animals, plants and bacteria. Ferritin forms a nanocage structure in which up to 4500 iron atoms can be accommodated [1]. The diameter and inner cavity are approximately 12 and 8 nm, respectively [2]. Ferritin is composed of 24 subunits of two types known as heavy (H) and light (L) chains, classified according to the subunit molecular weight, 21 and 19 kDa, respectively [1,2]. The nanocage structure reversibly assembles and disassembles depending on the pH conditions. The pH-dependent structures of ferritin have been investigated by synchrotron small-angle X-ray scattering (SAXS) [3]. It has been found that the intact hollow spherical ferritin was stable over the pH range 3.40–10.0, while stepwise disassembly of the hollow sphere takes place below pH 3.40. Since these unique features could play an important role in developing a molecular capsule or container, much attention has been paid to ferritin in fields including nanocomposite materials, semiconductors, drug delivery system (DDS) and so on [[4], [5], [6], [7]]. In fact ferritin forms a nanocage structure with several channels through which metal ions and/or organic molecules could pass in vivo, however, ferritin could function as an attractive molecular capsule if one can control the reversible assembly reaction.

The interface between two immiscible electrolyte solutions (ITIES) is a useful model for biomembrane systems in which charge transfer and adsorption processes are controlled as a function of the Galvani potential difference between two liquid phases [8,9]. The physicochemical study of bioactive species in biomimetic liquid–liquid systems is important since it is difficult to investigate in vivo the complicated pharmacokinetics involved in molecular association, acid-base equilibrium and distribution on or across a biomembrane [[10], [11], [12]]. Furthermore, electrochemical ion transfer at the ITIES offers an attractive label-free method of determining non-redox active species [13]. There are a number of studies of the electrochemical characterization and determination of small ionizable drugs [[14], [15], [16]], polyelectrolytes [17], macromolecules [18,19], and proteins [[20], [21], [22], [23]] at the ITIES. We have recently investigated the interfacial mechanism of dendritic polymers and their association behavior with anionic water-soluble porphyrins [24], ionizable drugs [25] and bioactive flavin species [26] through spectroelectrochemical techniques. In these works, it was demonstrated that NH2- and COOH-terminated polyamidoamine (PAMAM) dendrimers are useful molecular capsules and that hyperbranched polymers are pharmacokinetic modifiers of bioactive species.

In this study, the voltammetric behavior of ferritin was studied at the water|1,2-dichloroethane (DCE) interface prior to an application of ferritin as a molecular capsule for a functional DDS. The influence of pH, the concentration of ferritin and the organic supporting electrolyte, and the effect of repetitive sweeps on the voltammetric response were investigated.

Section snippets

Reagents

Ferritin from equine spleen (F4503) was purchased from Aldrich and used as received. The concentration of ferritin was calculated by using the molecular weight of the peptides (ca. 440 kDa). 1.0 × 10−2 mol dm−3 LiCl and 5.0 × 10−3 mol dm−3 bis(triphenylphosphoranylidene)ammonium tetrakis(pentafluorophenyl)borate (BTPPATPFB) were used as supporting electrolytes for the aqueous and organic phases, respectively. BTPPATPFB was prepared by metathesis of bis(triphenylphosphoranylidene)ammonium

Results and discussion

Typical cyclic voltammograms (CVs) measured for ferritin under various pH conditions are shown in Fig. 2a. CVs obtained under acidic conditions varied gradually depending on the repetitive sweeps (discussed later). Unless otherwise noted, therefore, the CVs obtained after 5 repetitive sweeps are used for the following discussion. No obvious voltammetric responses were observed in the potential window under neutral and alkaline conditions. However, at pH 2.1, anodic and cathodic peaks were

Conclusions

The voltammetric investigation revealed that the electrochemical behavior of ferritin at the polarized liquid|liquid interface was dependent on the pH. In acidic conditions where ferritin is disassembled to subunits, the current responses were drastically increased in the positive potential region. This result demonstrated that ferritin subunits have large positive charges. Ferritin subunits provided two distinguishable voltammetric responses during the forward and reverse sweeps. The

Conflict of interest

There is no conflict of interest.

Acknowledgements

The authors are grateful for valuable discussions with Mr. Ryota Kenmotsu of Okayama University of Science.

References (30)

  • H. Nagatani et al.

    Spectroelectrochemical analysis of ion-transfer and adsorption of the PAMAM dendrimer at a polarized liquid|liquid interface

    Electrochim. Acta

    (2008)
  • E.C. Theil

    Ferritin: structure, gene regulation, and cellular function in animals, plants, and microorganisms

    Annu. Rev. Biochem.

    (1987)
  • M. Kim et al.

    pH-dependent structures of ferritin and apoferritin in solution: disassembly and reassembly

    Biomacromolecules

    (2011)
  • G. Jutz et al.

    Ferritin: a versatile building block for bionanotechnology

    Chem. Rev.

    (2015)
  • L.P.H. Estrada et al.

    Protein nanoparticles for therapeutic protein delivery

    Biomater. Sci.

    (2015)
  • Cited by (17)

    • Interfacial association of ferritin with anionic fluorescent probe at the 1,2-dichloroethane/water interface

      2021, Journal of Electroanalytical Chemistry
      Citation Excerpt :

      On the other hand, the molecular association behavior between ionic species and dendritic polymers at ITIES has been elucidated through the spectroelectrochemical analysis, in which the interfacial reaction mechanisms of ionic species were reversibly controlled by the interaction with dendritic polymers under the appropriate potential [22–24]. Recently, we have reported the voltammetric behavior of ferritin at the polarized 1,2-dichloroethane (DCE)/water interface, suggesting its specific adsorption at the interface and the facilitated ion transfer of the organic anions [25]. In the present study, the spectroelectrochemical analysis of ferritin has been conducted by employing a fluorescent probe, 8-anilino-1-naphthalenesulfonate (ANS−), in order to elucidate the interfacial association of ferritin with anionic species in detail.

    • Electrochemistry of catalase at a liquid|liquid micro-interface array

      2021, Bioelectrochemistry
      Citation Excerpt :

      But at aqueous phase of pH 5.5 (the natural pH of 10 mM LiCl), no obvious CV response was observed (Fig. 1(b)), on comparison of CVs in the absence (black dashed line) and in the presence of 2 µM CAT (black solid line). In respect of this observed pH dependence, CAT behaves like other proteins at the ITIES, e.g. ferritin [43], insulin [44], lysozyme [44], myoglobin [29], haemoglobin [45], where below the pI of CAT (pI 5.4) [9], it is protonated and cationic in nature. But when the aqueous phase pH is higher than the pI of CAT, it is anionic in nature and no definite voltammetric response was found.

    • Co-deposition of silica and proteins at the interface between two immiscible electrolyte solutions

      2020, Bioelectrochemistry
      Citation Excerpt :

      Further polarization, together with the accumulated positive or negative charge within defined locus, facilitates the transfer of the organic phase background electrolyte anions or cations, respectively. This type of interfacial behaviour was reported for dendrimers (poly-L-lysine [13]; poly(propylamine) [14]; poly(amidoamine) [14,15] or carboxyl terminated-poly(amidoamine) [16]), polyelectrolytes (poly(diallyl dimethylammonium chloride) [17]; chitosan [18] protamine [19]; heparin [20]), proteins (e.g. ferritin [21] haemoglobin (Hb) [22,23]; myoglobin [24]; insulin [25]; cytochrome [26]) or DNA (thrombin binding aptamer [27]). Resulting deposits usually reside at the interface in a form of thin films.

    • Electrochemistry of proteins at the interface between two immiscible electrolyte solutions

      2018, Current Opinion in Electrochemistry
      Citation Excerpt :

      Electrochemical parameters indicate also that multi-layer films of adsorbed protein are formed at the interface. Systematic studies of pH with a range of proteins revealed that this indeed was the case (lysozyme [15], insulin [13], haemoglobin [12], cytochrome c [10,11], myoglobin [17], serum albumin [18]) and most recently, ferritin [19] and thrombin [20] have been shown to react exactly as predicted. Such behaviour has been summarised in a range of reviews/chapters [21,22].

    • Acid phosphatase behaviour at an electrified soft junction and its interfacial co-deposition with silica

      2018, Electrochemistry Communications
      Citation Excerpt :

      The interface between two immiscible electrolyte solutions (ITIES) emerges as a unique analytical platform with detection arising from interfacial charge transfer reactions including ions or electrons [4]. Proteins, when (positively) charged, can undergo potential-dependent adsorption to the ITIES, as has been found for haemoglobin [5], lysozyme [6], insulin [7], myoglobin [8], albumin [7] and ferritin [9], amongst others. Proteins and synthetic multi-charged macromolecules (e.g. polyelectrolytes [10], dendrimers [11]) can be considered to have similar interfacial charge-transfer characteristics.

    View all citing articles on Scopus
    View full text