(Top row) Iron oxidation kinetics at 305 nm under low oxygen concentration using (a) HosF (1.0 μM), Fe(II) (200 μM), and approximately 19 μM O2; (b) HL (0.2 μM), Fe(II) (140 μM), and approximately 11 μM of O2; (c) HuHF (0.4 μM),Fe(II) (500 μM), and approximately 30 μM O2. (Middle row): Dependence of the reaction rates on the concentration of remaining O2, calculated assuming 4:1 FeII:O2 stoichiometry. Red and green curves are kinetics before and after correction (more details in the text). (Lower row) Michaelis-Menten fit to the corrected kinetic curves for the calculation of Km and Vmax parameters.