Direct electron transfer reactions between human ceruloplasmin and electrodes

Abstract

In an effort to find conditions favouring bioelectrocatalytic reduction of oxygen by surface-immobilised human ceruloplasmin (Cp), direct electron transfer (DET) reactions between Cp and an extended range of surfaces were considered. Exploiting advances in surface nanotechnology, bare and carbon-nanotube-modified spectrographic graphite electrodes as well as bare, thiol-and gold-nanoparticle-modified gold electrodes were considered, and ellipsometry provided clues as to the amount and form of adsorbed Cp. DET was studied under different conditions by cyclic voltammetry and chronoamperometry. Two Faradaic processes with midpoint potentials of about 400 mV and 700 mV vs. NHE, corresponding to the redox transformation of copper sites of Cp, were clearly observed. In spite of the significant amount of Cp adsorbed on the electrode surfaces, as well as the quite fast DET reactions between the redox enzyme and electrodes, bioelectrocatalytic reduction of oxygen by immobilised Cp was never registered. The bioelectrocatalytic inertness of this complex multi-functional redox enzyme interacting with a variety of surfaces might be associated with a very complex mechanism of intramolecular electron transfer involving a kinetic trapping behaviour.

Interfacial Behavior and Activity of Laccase and Bilirubin Oxidase on Bare Gold Surfaces

“…A bulk enzyme concentration of 4 mg mL −1 was chosen, a value similar to those used in previous studies. 9,11,12 The MCOmodified Au surfaces were imaged by operating the AFM in both tapping and PFT modes (Figure 1c,d). A granular structure similar to that of clean Au was found for these surfaces.…”

“…These included both simple, long-standing explanations in the field of redox protein/metal interface electrochemistry, 13 associated with enzyme denaturation on bare Au surfaces or/and the absence of a heterogeneous ET between Au and active centers of MCOs, 14,15 as well as a sophisticated hypothesis involving the formation of inactive forms of MCOs as a result of an unnatural ET pathway resulting from enzyme orientation specifically by the trinuclear Cu cluster (Cu-T23), which was assumed to be in DET contact with the Au surfaces. 6,7,11,12,16 Recently, the well-pronounced DET-based bioelectrocatalytic reduction of O 2 on Au electrodes modified with Lc and BOx was demonstrated. It should be emphasized, however, that bioelectrocatalysis was observed only in the case of atomically planar Au(111) electrodes, 17,18 specifically modified polycrystalline Au surfaces, 19,20 and 3D (porous) Au electrodes.…”

“…In doing so, the index was fitted according to the method described by McCrackin and co-workers. 31 When assuming the refractive index, two values were taken into account: one based on our own work (n = 1.65) 12 and another based on previously reported results n = 1.45. 34 Because of the complexity in evaluating the thicknesses of thin protein layers on Au, as discussed further in the Results and Discussion section, we evaluated the trends (differences between conditions and enzymes) in thickness rather than the absolute values.…”

Oxygen Electroreduction versus Bioelectroreduction: Direct Electron Transfer Approach

“…For instance, non‐turnover signals for another BMCO, ceruloplasmin (Cp), were clearly observed indicating efficient DET, but pronounced bioelectrocatalytic currents for the enzyme were not registered . Based on detailed investigations of the enzyme it was suggested that the absence of bioelectrocatalysis seems to be related to the ordered mechanism of Cp function . Moreover, only very recently even MET based bioelectrocatalytic activity of this enzyme has been shown (Figure A) .…”

“…The mechanism of O 2 bioelectrocatalytic reduction by different BMCOs, e.g . BOx, plant, fungal, and bacterial Lc, was the subject of investigation in many studies . The ET mechanism is schematically presented in Figure using one of the most studied BMCOs, fungal Trametes Lc, as an example.…”