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In the present work, Ion Jelly films based on 1‐ethyl‐3‐methylimidazolium ethylsulfate, with incorporated redox proteins and enzymes were deposited on carbon screen‐printed electrodes (SPEs), and their electrochemical characterization was attained. Ion Jelly synthesis was carried out simultaneously with protein incorporation in its structure, followed by a maturation step under controlled atmosphere (4 days at 4 °C and water activity (aw) of 0.76). The electrochemical response of the material was characterized, and a sandwich‐type fuel cell configuration was subsequently built, consisting of two SPEs containing two independent Ion Jelly discs in the middle; one disc incorporated Desulfovibrio gigas cytochrome c3 and [NiFe]‐hydrogenase, while the other disc contained aldehyde oxidoreductase, constituting the biocathode and bioanode of the cell, respectively. Cell voltage increased with time in the presence of benzaldehyde, in agreement with a successful electronic pathway across the cell and the concomitant aldehyde oxidoreductase enzymatic activity. In the cathodic side assays, hydrogenase showed catalytic activity towards H+ reduction to H2.
In the present work, Ion Jelly films based on 1‐ethyl‐3‐methylimidazolium ethylsulfate, with incorporated redox proteins and enzymes were deposited on carbon screen‐printed electrodes (SPEs), and their electrochemical characterization was attained. Ion Jelly synthesis was carried out simultaneously with protein incorporation in its structure, followed by a maturation step under controlled atmosphere (4 days at 4 °C and water activity (aw) of 0.76). The electrochemical response of the material was characterized, and a sandwich‐type fuel cell configuration was subsequently built, consisting of two SPEs containing two independent Ion Jelly discs in the middle; one disc incorporated Desulfovibrio gigas cytochrome c3 and [NiFe]‐hydrogenase, while the other disc contained aldehyde oxidoreductase, constituting the biocathode and bioanode of the cell, respectively. Cell voltage increased with time in the presence of benzaldehyde, in agreement with a successful electronic pathway across the cell and the concomitant aldehyde oxidoreductase enzymatic activity. In the cathodic side assays, hydrogenase showed catalytic activity towards H+ reduction to H2.
A comparative study of direct and mediated electrochemistry of metalloproteins in bulk and membrane-entrapped solutions is presented. This work reports the first electrochemical study of the electron transfer between a bacterial cytochrome c peroxidase and horse heart cytochrome c. The mediated catalysis of the peroxidase was analysed both using the membrane electrode configuration and with all proteins in solution. An apparent Michaelis constant of 66 +/- 4 and 42 +/- 5 microM was determined at pH 7.0 and 0 M NaCl for membrane and bulk solutions, respectively. The data revealed that maximum activity occurs at 50 mM NaCl, pH 7.0, with intermolecular rate constants of (4.4 +/- 0.5) x 10(6) and (1.0 +/- 0.5) x 10(6) M(-1) s(-1) for membrane-entrapped and bulk solutions, respectively. The influence of parameters such as pH or ionic strength on the mediated catalytic activity was analysed using this approach, drawing attention to the fact that careful analysis of the results is needed to ensure that no artefacts are introduced by the use of the membrane configuration and/or promoters, and therefore the dependence truly reflects the influence of these parameters on the (mediated) catalysis. From the pH dependence, a pK of 7.5 was estimated for the mediated enzymatic catalysis.
In this work it is demonstrated that the characterization of c-type haem containing proteins by electrochemical techniques needs to be cautiously performed when using pyrolytic graphite electrodes. An altered form of the cytochromes, which has a redox potential 300 mV lower than that of the native state and displays peroxidatic activity, can be induced by interaction with the pyrolytic graphite electrode. Proper control experiments need to be performed, as altered conformations of the enzymes containing c-type haems can show activity towards the enzyme substrate. The work was focused on the study of the activation mechanism and catalytic activity of cytochrome c peroxidase from Paracoccus pantotrophus. The results could only be interpreted with the assignment of the observed non-turnover and catalytic signals to a non-native conformation state of the electron-transferring haem. The same phenomenon was detected for Met-His monohaem cytochromes (mitochondrial cytochrome c and Desulfovibrio vulgaris cytochrome c-553), as well as for the bis-His multihaem cytochrome c(3) from Desulfovibrio gigas, showing that this effect is independent of the axial coordination of the c-type haem protein. Thus, the interpretation of electrochemical signals of c-type (multi)haem proteins at pyrolytic graphite electrodes must be carefully performed, to avoid misassignment of the signals and incorrect interpretation of catalytic intermediates.
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