Stopped-flow absorbance traces for the reaction of 300 μM TrpH/Fe(II) with oxygen in the absence (A) or presence of 400 μM tryptophan (B). The final concentrations of oxygen were 600 μM (circles), 300 μM (squares), 125 μM (diamonds) and 80 μM (triangles). Only 5% of the points are shown for clarity. The lines are from global simulations (KinTek Explorer Pro) of the reactions at all four oxygen concentrations using a second order irreversible reaction with a rate constant of 104 M−1s−1. Conditions: 150 mM HEPES/NaOH, 100 mM ammonium sulfate, 20% glycerol, pH 7.0, 5 °C