Comparative Study of ~17O and ~18O Isotope Effects As a Probe for Dioxygen Activation: Application to the Soybean Lipoxygenase Reaction

摘要

We present the first comparative study of ~17O and ~18O isotope effects in a dioxygen-dependent enzymatic reaction. The binding of dioxygen to soybean lipoxygenase is expected to be near the diffusive limit, introducing the possibility of a magnetic isotope effect with ~17O reacting faster than ~16O. However, the experimental data indicate a purely mass effect among the ~16O, ~17O, and ~18O isotopes. A reaction mechanism for soybean lipoxygenase is proposed in which dioxygen undergoes reversible reaction with a substrate derived radical, followed by a slow release of the bound lipid hydroperoxide.