Amperometric flow-type l-histidine sensor using an immobilized galactose oxidase reactor, based on a novel catalytic activity induced by exogenous histidine

The specificity of galactose oxidase (GAO; EC. 1.1.3.9, from dactylium dendroides) has been drastically changed upon the addition of l-histidine (His), and the GAO catalyzes an air oxidation of l-ascorbate (AsA). The ESR signal of copper (II) at active site of GAO at 77 K was drastically changed upon the addition of His indicating that extrinsic His binds at active copper site of GAO and leads to the change in the coordination structure. This His-induced reaction of GAO was applicable to the flow-injection analysis system for detecting His with an immobilized GAO reactor and an AsA-containing carrier. The peak-shape current response for His has been observed when 0.1 M Tris–HCl buffer (pH 8.5) containing 5 mM AsA was used as a carrier at 0.5 ml/min and 35°C. The calibration graph of His exhibits the linear line in the concentration up to 1×10−2 M His with detection limit of 5×10−6 M.