Recognition of substrates by membrane potential of immobilized enzyme membranes

Abstract

The membrane potential and its shifts, caused by the injection of substrates into a permeation cell, were measured by using immobilized glucose oxidase membranes. No shift in membrane potential was observed for the injection of caffeine and galactose, but there was a shift for D- and L-glucose. Response plots for D-glucose showed that a slope of 10.8 mV per concentration decade was observed over a linear range of 3 × 10^–3–10^–1 mol dm^–3 with a detection limit of 1 mmol dm^–3D-glucose. The shift in membrane potential was considered to be generated by change of charge density in the enzyme membrane due to the binding of glucose to the enzyme. Since the enzyme did not react with L-glucose but did react with D-glucose, it is considered that L-glucose can bind with the enzyme, but cannot react with oxygen and gives no product. It is suggested that the high specificity of the reaction between the enzyme and substrates is generated not only by the specific binding sites on the enzyme but also by stereochemical interaction.