Screen-printed graphite macroelectrodes for the direct electron transfer of cytochrome c: a deeper study of the effect of pH on the conformational states, immobilization and peroxidase activity

Gomez-Mingot, M, Montiel, V, Banks, CE and Iniesta, J (2014) Screen-printed graphite macroelectrodes for the direct electron transfer of cytochrome c: a deeper study of the effect of pH on the conformational states, immobilization and peroxidase activity. ANALYST, 139. ISSN 0003-2654

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Abstract

The direct electron transfer of cytochrome c has been studied at screen-printed graphite macroelectrodes without recourse to mediators or the need for any electrode pre-treatment as is commonly employed within the literature. A wide range of pH values from 2.0 to 11.0 have been explored upon the electrochemical response of cytochrome c and different voltammetric signatures have been observed. The direct electron transfer of the alkaline transition of cytochrome c was found impeded within alkaline media leading to either an irreversible redox process or even no voltammetric responses. In acidic aqueous media the electrochemical process is observed to undergo a mixed diffusion and adsorption controlled process rather than a purely diffusional process of the native conformation as observed at pH 7.0. Interestingly, at pH 3.5 a new conformational state is revealed in cooperation with the native conformation. The immobilization of the protein was satisfactorily obtained using a simple method by cycling the protein at specific solution pH values allowing amperometric responses to be obtained and gives rise to useful pseudo-peroxidase activity for sensing H2O2. Apparent Michaelis–Menten constant values (Km) were calculated via the Lineweaver–Burk method with deduced values of 25 4, 98 12 and 230 30 mM, respectively for pH values of 2.0, 3.0 and 7.0. Such work is important for those utilising cytochrome c in bio-electrochemical and related applications.