Abstract
On the basis that choline, produced from cholinester by cholinesterase (ChE), is oxidized by choline oxidase to hydrogen peroxide, the blood plasma ChE activity was determined by advancing the 2 succesive reactions in a single reaction cell, and electrochemically measuring the hydrogen peroxide of the final product. The enzyme electrode, consisting of an immobilized choline oxidase membrane and a hydrogen peroxide probe, was employed for the second reaction and the assay of hydrogen peroxide. The most suitable ChE analysis included addition of 10μl of 4 mM ACh and 10μl of plasma in 1 ml of 1/15 M phosphate buffer (pH 8.0) in the reaction cell, incubating the mixture for 2 min at 37°C and recording the hydrogen peroxide yield during the incubation. The ChE activity was expressed as mM of choline formed/ml of plasma/min of reaction, calibrated from the amount of hydrogen peroxide produced. The ChE activity from normal human- or MEP-treated rabbit blood, determined by the present method, had good correlation with that of the DTNB method or the ΔpH method. The reaction was 4.5 to 7.5 %, compared to 12 to 14 % by the DTNB method, and the enzyme electrode was stable for up to 25 repeated examinations. The enzyme electrode method could thus be available for the rapid and simplified determination of blood plasma ChE activity.
