a), The Stc operon from S. meliloti 1021 and the proposed Stc2-catalyzed N-demethylation reaction using its biological reductases Stc3 and Stc4. b), Stc2-catalyzed N-demethylation reaction using a photo-reduction system with the help of photo-sensitizers (PS). c), The overall structure of Stc2 trimer. d), Stc2 active site, including its mononuclear non-heme iron site, the Rieske-type [2Fe-2S]2+ cluster on an adjacent subunit, and Glu201 used to link them.