ELECTRON-TRANSFER OF HORSE SPLEEN FERRITIN AT GOLD ELECTRODES MODIFIED BY SELF-ASSEMBLED MONOLAYERS

Electron transfer is known to be an important step in the sequestering of iron by cellular ferritin. In this work, direct electron transfer between ferritin and a gold electrode was performed in order to probe its electron transfer kinetics. Gold electrodes were modified by the f ormation of self-assembled monolayers of 3-mercapto-propionic acid on the gold surface. Cyclic voltammetry using these electrodes shows that ferritin exhibits slow electron transfer kinetics at low potentials, yet fairly well-defined current-potential curves. In addition, the vol tammetry indicates that adsorption of ferritin precedes the electron t ransfer step. Controlled potential electrolysis measurements yielded a n n-value of 1910 electrons transferred per mole of ferritin. Cyclic v oltammetry of a solution containing ferritin as well as nitrilotriacet ate yields no electrolytic currents at potentials where the iron-nitri lotriacetate complex undergoes redox reactions, indicating that the cu rrents observed in the voltammetry of ferritin were not due to free ir on in the ferritin sample. In addition, the voltammetry of iron-free f erritin (apoferritin) did not yield appreciable currents, providing ad ditional support to the suggestion that the observed voltammetric curr ents were due to the redox reactions of ferritin iron. Self-assembled monolayers containing carboxylate end groups effectively promoted the direct electron transfer of ferritin at a gold electrode, thus demonst rating that the electron transfer mechanisms of ferritin can now be pr obed electrochemically.