Interaction of bacterial luciferase with 8-substituted flavin mononucleotide derivatives.

Bacterial luciferase catalyzes the emission of visible light from the reaction of reduced flavin, molecular oxygen, and an n-alkyl aldehyde. The mechanism of the reaction was probed by measuring the electronic effects of various substituents at the 8-position of the flavin ring system. Substituent effects were obtained for CH3-, Cl-, CH3O-, CH3S-, F-, and H- on the rate of formation and decay of the hydroperoxyflavin intermediate and the time courses for the emission of visible light. The rate constant for the decay of light emission increases for the series Cl < F < H < CH3S < CH3 < CH3O. These results are not compatible with a standard Baeyer-Villiger type mechanism for the chemical transformation, but they are consistent with a decrease in the electron density at the reaction center of the flavin moiety during the rate-limiting step of the reaction.