CHEMICAL AMPLIFICATION OF URIC-ACID SENSOR RESPONSES BY DITHIOTHREITOL

The consumption of oxygen caused by the uricase reaction can be significantly amplified when the reaction is performed in the presence of dithiothreitol. As a result, chemically amplified current responses of uric acid using the immobilized uricase electrode were obtained. This amplified current response was increased with increasing dithiothreitol concentrations in the sample solution, and the amplification factor for a 1 x 10(-6) M uric acid solution was increased to 133 when 5 x 10(-2) M dithiothreitol solution (pH 9.1) was used. During amplification, the ESR signal of hydroxyl radicals was increased along with amplification. These facts suggest that uric acid is regenerated by the reduction of ternary complex consisting of enzyme, uric acid, and oxygen and by the accompanying formation of the hydroxyl. radical from the coordinated oxygen. An increase in hydroxyl radical was not observed in the presence of superoxide dismutase, suggesting that the coordinated oxygen was converted to a hydroxyl radical via the superoxide anion. The latter probably remains coordinated in the ternary complex, since no ESR signal for superoxide anion was detected during the experiments.