Figure 6.
Kinetics of the formation of the NR 1 upon oxidation of 5 mM solution of the HA 1H in deaerated 0.1 M Na-phosphate buffer, pH 7.6, 0.1 mM DTPA, in the presence of various concentrations of the dehydroascorbic acid, 2 mM (□) and 5 mM (■), measured by EPR as described in the Materials and Methods. Solid lines are the best fits of the experimental data to equations (1-4) assuming the rate constant of monomolecular decomposition of dehydroascorbic acid, k4 = (6.8±0.5)×10−4s−1 and the rate constant of hydroxylamine oxidation by the ascorbate radical, k−1 = (1.05±0.05)×103 M−1s−1 yielding the bimolecular rate constant of hydroxylamine oxidation by dehydroascorbic acid, k2 = (1±0.25)×10−2 M−1s−1.
