Dicamba monooxygenase (DMO) catalyzes the O-demethylation of dicamba (3,6-dichloro-2-methoxybenzoate) to produce 3,6-dichlorosalicylate and formaldehyde. Recent crystallographic studies suggest that DMO catalyzes the challenging oxidation of a saturated C-H bond within the methyl group of dicamba to form a hemiacetal intermediate. Testing of this hypothesis was made possible by our development of two new independent techniques. As a novel method to allow use of 18O2 to follow reaction products, bisulfite was used to trap newly formed 18O-formaldehyde in the stable adduct, hydroxymethanesulfonate (HMS-), and thereby prevent the rapid exchange of 18O in formaldehyde with 16O in water. The second technique utilized unique properties of Pseudomonas putida formaldehyde dehydrogenase that allow rapid conversion of 18O-formaldehyde into stable and easily detectable 18O-formic acid. Experiments using these two new techniques provided compelling evidence for DMO-catalyzed oxidation of the methyl group of dicamba, thus validating a mechanism for DMO [and for vanillate monooxygenase, a related Rieske nonheme iron monooxygenase] that involves the difficult oxidation of a saturated C-H bond.
ASJC Scopus subject areas
- Molecular Medicine