Electrochemical properties of pH-dependent flavocytochrome c₃ from Shewanella putrefaciens adsorbed onto unmodified and catechol-modified edge plane pyrolytic graphite electrode

The electroactivity of adsorbed flavocytochrome c₃, a tetraheme FAD-containing flavoenzyme isolated from the bacterium Shewanella putrefaciens, is investigated by cyclic voltammetry at an edge plane pyrolytic graphite electrode before and after modification with grafted catechol serving as an efficient pH sensor based on a redox readout. Flavocytochrome c₃ adsorption onto the unmodified or modified electrode surface is successfully achieved by cyclic voltammetry (100 consecutive cycles) in a flavocytochrome c₃ solution containing polymyxin as co-adsorbate. The immobilized flavocytochrome c₃ retains its electrochemical activity and its catalytic fumarate reductase activity. The redox activity of the protein arises from its FAD and four hemes cofactors. The experiments evidence that the hemes' redox potential of flavocytochrome c₃ from Shewanella putrefaciens, for which no crystal structure is yet available, depend on pH which is at variance with data from the other strains Shewanella frigidimarina or Shewanella oneidensis.