Direct electrochemistry and catalysis of heme-proteins entrapped in methyl cellulose films

Myoglobin and hemoglobin was immobilized on edge-plane pyrolytic graphite (EPG) electrodes by methyl cellulose (MC). Both the proteins entrapped in the MC film underwent fast direct transfer-electron reactions, corresponding to hemeFeIII + e− → hemeFeII. The formal potential (E0′), the apparent coverage (Γ), the electron transfer coefficient (α) and the apparent electron transfer rate constant (ks) were calculated by performing non-linear regression analysis of SWV experimental data. E0′ was linearly dependent on the solution pH (redox Bohr effect), indicating the electron transfer of the FeIII/FeII redox couple accompanied by the transfer of proton. UV–Vis absorption (UV–Vis) and reflection–absorption infrared (RAIR) spectra suggested that the proteins keep their original conformation in the MC film. The conformation changed reversibly in the range of pH values investigated (3.0–9.0). Atomic force microscopy (AFM) images suggested a strong interaction between the heme proteins and MC. The processes of catalytic reduction of oxygen, hydrogen peroxide and nitric oxide by Mb and Hb entrapped in MC film were also explored.