Electron transfer mediated by membrane-bound d-fructose dehydrogenase adsorbed at an oil/water interface.

Abstract The catalytic activity of a membrane-bound enzyme, d -fructose dehydrogenase (FDH), at the polarized oil/water (O/W) interface was studied. Multisweep cyclic voltammetry and ac voltammetry were carried out to show the irreversible adsorption of FDH at the interface. Using the thusly prepared FDH-adsorbed O/W interface, clear steady-state catalytic current was observed in amperometry and cyclic voltammetry, where 1,1′-dimethylferrocenium ion (DiMFc + , electron acceptor) and d -fructose (substrate) were added to the O and W phases, respectively. The observed catalytic current was then analyzed by using two mechanisms. In mechanism (A), the heme c site of FDH, where DiMFc + is reduced, was assumed to be located in the O-phase side of the interface. The intramolecular electron transfer in FDH should be affected by the Galvani potential difference of the interface ( Δ O W ϕ ). However, the theoretical equations derived for the catalytic current could not reproduce the experimental data. In mechanism (B), the heme c site was assumed to be in the W-phase side. In this case, Δ O W ϕ should affect the interfacial distribution of DiMFc + . This mechanism could reproduce well the observed potential dependence of the catalytic current.