Dicamba (2-methoxy-3,6-dichlorobenzoic acid) O-demethylase (DMO) is the terminal Rieske oxygenase of a three-component system that includes a ferredoxin and a reductase.It catalyzes the NADH-dependent oxidative demethylation of the broad leaf herbicide dicamba.DMO represents the first crystal structure of a Rieske non-heme iron oxygenase that performs an exocyclic monooxygenation, incorporating O 2 into a side-chain moiety and not a ring system.t catalyzes the NADH-dependent oxidative demethylation of the broad leaf herbicide dicamba. DMO represents the first crystal structure of a Rieske non-heme iron oxygenase that performs an exocyclic monooxygenation, incorporating O 2 into a side-chain moiety and not a ring system.