Electron transport catalyzed by a membrane-bound enzyme, d-fructose dehydrogenase (FDH), from one aqueous phase (W1) containing d-fructose to another one (W2) containing [Fe(CN)6]3− across a planar bilayer lipid membrane (BLM) containing 7,7,8,8-tetracyanoquinodimethane (TCNQ) was investigated electrochemically. We found that the ion transport across the BLM was driven at the same time by the electromotive force generated by the electron transport.
Proton transport from an aqueous phase (W1) to another one (W2) across a planar bilayer lipid membrane (BLM) was driven by the electron transport system. The electron transport system was composed of the oxidation of D-fructose by an oxidized form of D-fructose dehydrogenase (FDH) at the W1|BLM interface, the oxidation of a reduced form of FDH by an oxidized form of 7,7,8,8-tetracyanoquinodimethane (TCNQ) at the W1|BLM interface and the oxidation of a reduced form of TCNQ by [Fe(CN) 6 ] 3− at the W2|BLM interface. Then the negative current due to the electron transfer from W1 to W2 was clearly observed around 0 V. The zero-current potential varied to hold the electroneutrality in all phases by balancing the proton transport with the electron transport.
Ion transport from one aqueous phase (W1) to another (W2) across a planar bilayer lipid membrane (BLM) in the presence of inhalation anesthetics was electrochemically investigated. In the absence of inhalation anesthetics in the BLM system, no ion transport current flowed between W1 and W2 across the BLM. When inhalation anesthetics such as halothane, chloroform, diethyl ether and trichloroethylene were added to the two aqueous phases or the BLM, the ion transport current quite clearly appeared. When the ratio of the concentration of KCl or NaCl in W1 to that in W2 was varied, the zero current potential across the BLM was shifted. By considering the magnitude of the potential shift, we concluded that the ion transport current can be predominantly ascribed to the transport of Cl(-) across the BLM. Since the dielectric constants of these anesthetics are larger than that of the inner hydrophobic domain of the BLM, the concentration of hydrophilic electrolyte ions in the BLM increases with the increase in the dielectric constant of the inner hydrophobic domain caused by addition of these anesthetics. These situations lead to an increase in the ion permeability coefficient.
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