Composite films of surfactants, nation, and proteins with electrochemical and enzyme activity

Stable, functional composite films were made from the ionomer Nafion, water-insoluble surfactants, and heme proteins or the enzyme alcohol dehydrogenase. Rates of electron transfer between myoglobin (Mb) and. hemoglobin (Hb) and edge plane pyrolytic graphite (PG) electrodes in these composite films were much larger than those for Hb and Mb in solution on Nafion-coated or bare PG electrodes. Films containing Nafion, didodecydimethylammanium bromide (DDAB), and hemoglobin or myoglobin retained about 90% of the initial redox activity during 4 weeks of storage at 4 degrees C. DDAB is arranged in lamellar Liquid crystal bilayers in these films at 25 degrees C, which were more stable than films of the proteins and DDAB alone. Films of Nafion-lecithin-Cyt c on edge plane PG also had good electrochemical properties but were much less stable. Electronic and vibrational spectra indicate that the heme proteins are not denatured in the composite films, but conformational differences from the native state may exist. Linear dichroism suggests that the proteins are specifically oriented in these films. After treatment with a cross-linking agent, Nafion-lipid films containing the enzyme alcohol dehydrogenase retained twice the activity of the enzyme in solution (4 degrees C) when stored for 2 days at room temperature.