Fluorometric assay of tiopronin based on inhibition of multienzyme redox system

In this paper, a simple and sensitive fluorimetric method for the determination of tiopronin (N-(2-mercaptopropionyl)-glycine) is proposed. The method is based on the strong inhibitory effect of tiopronin on the multienzyme redox system of hemoglobin, nicotinamide adenine dinucleotide (NADH) and H2O2, in which the intrinsic fluorescence of NADH was employed as the detection signal. The calibration graph is linear in the range 6.13 × 10−7 to 6.13 × 10−6 M with a detection limit of 1.65 × 10−7 M and the relative standard deviation of 2.02%. Kinetics in the pseudo-first-order conditions was investigated by stopped-flow spectrofluorometry and the inhibition mechanism of tiopronin was verified of the competitive type.