Figure 6.

A and B, Kinetics of disappearance of NADH (200 µM) in the presence of MB (100 µM) in PBS (phosphate-buffered saline), at pH ranging between 7.4 and 7.5 (values given in the figure) and ambient temperature. The concentrations of NADH were determined based on the peak of absorbance in the ultraviolet range (340 nm). These data were used to determine the time at which all NADH would have disappeared from a solution, which initially contained MB, NADH, and H₂O. As NADH, but not MB, created an artifact for the determination of H₂O₂ (C and D), the reaction of the solution containing MB and NADH with the assay kit, was performed at 120 min, when all NADH was oxidized. In all tests, a peak of absorbance was observed at 570 nm corresponding to concentrations of H₂O₂ in the high µM range (D).