Lumazine protein and the excitation mechanism in bacterial bioluminescence

The spectral properties of lumazine protein and mixtures with the intermediates of the bacterial luciferase reaction, are reviewed. Measurements of fluorescence dynamics in particular have been employed with the aim of elucidating the mechanism by which lumazine protein functions in the bioluminescence of the bacteria of the type Photobacterium. The reaction of bacterial luciferase with its substrates produces bioluminescence emission with a spectral maximum at 496 nm. This spectrum is the same as the fluorescence of a luciferase flavin intermediate in the reaction, called the Fluorescent Transient. When lumazine protein is also present in the reaction; however, the bioluminescence emission now corresponds to the fluorescence of lumazine protein, which has a maximum at 475 nm. From measurements of the decay of fluorescence anisotropy of lumazine protein alone and in mixtures with the luciferase fluorescent transient, it is shown that a protein-protein complex is formed and that there is rapid energy transfer between the flavin on the luciferase and the lumazine derivative bound to its protein. An approximate calculation estimates the rate of this energy transfer to be faster than 10(9) s-1, and this would account for the efficient transfer of excitation from the flavin on the associated luciferase in the mixed protein bioluminescence reaction.