O-H Activation by an Unexpected Ferryl Intermediate during Catalysis by 2-Hydroxyethylphosphonate Dioxygenase

摘要

Activation of O—H bonds by inorganic metal-oxo complexes has been documented, but no cognate enzymatic process is known. Our mechanistic analysis of 2-hydroxyethylphosphonate dioxygenase (HEPD), which cleaves the C1—C2 bond of its substrate to afford hydroxymethyl-phosphonate on the biosynthetic pathway to the commercial herbicide phosphinothricin, uncovered an example of such an O—H-bond-cleavage event Stopped-flow UV—visible absorption and freeze-quench Mössbauer experiments identified a transient iron(IV)-oxo (ferryl) complex. Maximal accumulation of the intermediate required both the presence of deuterium in the substrate and, importantly, the use of ~2H_2O as solvent. The ferryl complex forms and decays rapidly enough to be on the catalytic pathway. To account for these unanticipated results, a new mechanism that involves activation of an O—H bond by the ferryl complex is proposed. This mechanism accommodates all available data on the HEPD reaction.