Kinetic method for enzymatic analysis by predicting background with uricase reaction as model

Objective:To investigate the reliability for kinetic assay of substance with background predicted by the integrated method using uricase reaction as model. Methods: Absorbance before uricase action (A0) was estimated by extrapolation with given lag time of steady-state reaction. With Km fixed at12.5 μmol/L, background absorbance (Ab) was predicted by nonlinearly fitting integrated MichaelisMenten equation to Candida utilis uricase reaction curve. Uric acid in reaction solution was determined by the difference (ΔA) between A0 and Ab. Results :Ab usually showed deviation ＜3% from direct assay with residual substrate ＜one-fifth of initial substrate for analysis. ΔA showed CV ＜5% with resistance to common interferences except xanthine, and it linearly responded to uric acid with slope consistent to the absorptivity of uric acid. The lower limit was 2.0 μmol/L and upper limit reached 30 μmol/L in reaction solution with data monitored within 8 min reaction at 0. 015 U/ml uricase. Preliminary application to serum and urine gave better precision than the direct equilibrium method without the removal of proteins before analysis. Conclusion:This kinetic method with background predicted by the integrated method was reliable for enzymatic analysis, and it showed resistance to common interferences and enhanced efficiency at much lower cost.