Structural and electron transfer properties of cytochrome c adsorbed on graphite electrode studied by in situ tapping mode AFM

We have investigated the adsorption of redox protein, cytochrome c, on graphite electrode from phosphate buffer by in situ tapping mode AFM. The protein adsorbs spontaneously onto the electrode that is covered with an adsorbed phosphate layer and forms a uniform monolayer. The adsorbed protein exhibits a reversible electron transfer at 0.17 V (Ag/AgCl) once the electrode has been increased to 0.75 V. We suggest that the adsorbed protein retains the folded conformation, and increasing the potential induces the protein to reorient its positively charged lysine residues towards the phosphate layer which promotes the electron transfer. (C) 1997 Elsevier Science B.V.