Fig. 5. Stopped-flow-absorption spectra demonstrating the accumulation of intermediate(s) in the reaction of the Fe(II)·AetD complex with O₂ in the presence of 5,7-dibromo-l-tryptophan at 5 °C.

a,b, Absorption spectra acquired after rapid mixing an O₂-free solution of AetD (0.30 mM) and Fe(II) (0.60 mM, 2 molar equiv.) in the absence (a) or presence (b) of 2 mM 5,7-dibromo-l-tryptophan, with an equal volume of O₂-saturated buffer (1.8 mM). c, Kinetic traces showing the accumulation and decay of the absorbing intermediates as a function of time in the presence of 2 mM 5,7-dibromo-l-tryptophan (initial concentration). The control without the substrate is shown in black. d, Kinetic traces of the intermediate with absorption maxima λ = 625 nm as a function of various Fe(II) molar equivalents in the presence of 2 mM 5,7-dibromo-l-tryptophan (initial concentration).