Structure of the oxygen adduct intermediate in the bacterial luciferase reaction: C nuclear magnetic resonance determination.

By using FMN enriched in (13)C (90%) at position C-4a, we have conclusively shown that the reaction of molecular oxygen with bacterial luciferase-bound FMNH(2) forms an adduct at the 4a position. Consistent with this are (13)C NMR studies of FMN and other flavin compounds which show that this carbon should be unusually reactive in the reduced 1,5-dihydroflavins with respect to electrophilic attacks.