Specific and amplified current responses to histidine and histamine using immobilized copper-monoamine oxidase membrane electrode, based on novel ascorbate oxidase activity induced by exogenous ligands.

Upon the addition of histidine and histamine, the copper containing monoamine oxidase (MAO) catalyzes the oxidation of L-ascorbic acid (AsA) by dissolved oxygen, in which the consumed oxygen was finally converted to hydrogen peroxide, according to Michaelis-Menten kinetics (Km) = 1.97 mM, upon the addition of 5 x 10(-5) M L-histidine at 35 degrees C and pH 8.5). The amount of oxygen consumption depended on the amount of histidine and histamine added, and specific responses over other amines were observed when the oxygen electrode modified with immobilized MAO membrane was used in the 0.1 M Tris buffer containing AsA. The calibration curves of L-histidine and histamine at 4 mM AsA exhibit linearity in the concentration range from 5 x 10(-7) to 5 x 10(-5) M L-histidine and 5 x 10(-6) to 1 x 10(-8) M histamine, with detection limit of 3 x 10(-7) M L-histidine and 3 x 10(-6) M histamine, respectively. The ESR signal of copper(II) in active site of MAO at 77K was apparently changed upon the addition of L-histidine and histamine indicating that exogenous histidine and histamine bound to the copper site of enzyme and lead to the structural change in active site.