Isotope fractionation plots for TauD (●), HppE (■), and ACCO (◆). The fits for obtaining 18O KIEs are shown in solid, dashed, and dotted lines, respectively.8 Conditions: TauD: 0.2 μM TauD, 0.4–0.6 mM O2, 2 mM taurine, 2 mM αKG, 0.2 mM ascorbate, 50 mM BisTris pH 6.2, 30 °C; HppE: 10μM HppE, 0.4–0.6 mM O2, 1 mM S-HPP, 11 μM FMN, 1.5 mM NADH, 20 mM Tris-HCl pH 7.5, 25 °C; ACCO: 5 μM ACCO, 0.3–0.5 mM O2, 3 mM ACC, 20 mM ascorbate, 20 mM NaHCO3, 100 mM NaCl, 100 mM MOPS pH 7.2, 25 °C.