Voltammetry of Cytochrome c3 from Desulfovibrio desulfuricans (strain Norway) at the Graphite Electrode

Interfacial reactions of cytochrome c3 at a graphite electrode were studied in a neutral medium by means of the differential pulse and cyclic voltammetry. It was found that ferricytochrome c3 yielded three cathodic peaks G, d i and Cm at potentials of —0.3 to —0.5 V (vs. Ag/AgCl reference electrode) on the voltammograms. Upon anodic polarization this protein yielded two anodic peaks Ai and An at 0.66 V and 0.89 V, respectively. It was suggested that peak G, appearing at relatively low concentrations of the protein (5 x 10~ mol/1), corresponded to a catalytic reaction, in which some of haemins of adsorbed molecules of ferricytochrome c3 were reduced to haems; these haemins could then be regenerated by chemical oxidation of the haem residues with oxygen adsorbed at the graphite surface. The next two cathodic peaks Cu and C m apparently corresponded to diffusion-controlled reduction of haemins bound in the nonadsorbed molecules of ferricytochrome c3. Anodic peaks Ai and An were suggested to correspond to electrode reactions identical to those corresponding to peaks A! and An of cytochrome c. This means that the electrooxidation of tyrosine residues is responsible for the appearance of the anodic peak Ai, whereas peak An corresponds to an anodic reaction of haemin residues.