Electron Transfer to a Gold Electrode from Cytochrome Oxidase in a Biomembrane via a Polyelectrolyte Film

We have developed an electrode modification, which permits the communication between cytochrome c in solution, cytochrome oxidase residing in its natural environment of a lipid membrane, and a gold electrode. The connection is made via an electroactive polyelectrolyte containing an osmium complex covalently attached to poly(4-vinylpyridine), sandwiched between thin layers of a negatively charged polyelectrolyte, polystyrene sulfonate. The outermost layer is the support for the oxidase-containing lipid film. Electron transfer from a pulse of reduced cytochrome c in the surrounding medium via the enzyme and the polyelectrolyte to the electrode is evident as a transient current during anaerobic conditions. Inhibiting the enzyme with sodium azide results in a temporarily decreased cytochrome c signal. The enzyme-mediated electron transport increased with increasing substrate concentration, resulting in a Michaelis−Menten constant of the same magnitude as for free or liposomal enzyme.