Chemiluminescent in vitro estimation of the inhibitory constants of antioxidants ascorbic and uric acids in Fenton's reaction in urine.

The goal of this research was to measure in vitro the inhibitory constants of the antioxidants ascorbic and uric acid in urine, with lucigenin enhanced chemiluminescence (CL) in Fenton's system. Maximum CL emission is registered in urine containing H2O2 (5.10(-4) M), Fe2+ (5.10(-5) M), EDTA (5.10(-5) M), and chemical enhancer lucigenin (10(-4) M) at pH 5.5 and 36 degrees C. Ascorbic acid exhibits up to 4-fold stronger antioxidant effect than uric acid. The constants of antioxidant inhibition in urine were measured at concentrations 10(-3) and 10(-4) M: for ascorbic acid, 5.92 +/- 0.04 and 24.05 +/- 1.82 micromol.sec(-1); for uric acid, 1.60 +/- 0.02 and 21.45 +/- 0.97 micromol.sec(-1), respectively. Three phases of CL kinetics of urine are well observed: spontaneous CL (0-10 sec), fast flash of CL (10-50 sec), and latent period (50-300 sec). The antioxidant efficiency of ascorbic and uric acids in the final stage of catabolic processes in the body is discussed.