Fatty acid-enhanced binding of flavin mononucleotide to bacterial luciferase measured by steady-state fluorescence

Bacterial luciferase catalyzes the oxidation of reduced flavin mononucleotide and tetradecanal resulting in the emission of light. We have investigated the interactions of a recombinant luciferase from a terrestrial bacterium Xenorhabdus luminescens with the reaction products, FMN and myristic acid, using steady-state fluorescence spectroscopy. Quenching of the intrinsic fluorescence and FMN fluorescence on binding of FMN to luciferase was found to be greatly stimulated in the presence of myristic acid, corresponding to a reduction of more than 30-fold in the FMN dissociation constant of the enzyme. In addition, the FMN-luciferase complex exhibits distinct fatty acid-dependent fluorescence properties. These results indicate that luciferase forms a ternary complex with FMN and myristic acid with a significantly different conformation from that of the binary FMN-luciferase complex.