Introduction and conclusions of book article
Bacterial luciferase can use FMN as well as various analogs in the bioluminescent reaction. These analogs have an effect on the bioluminescent spectrum and on the kinetics of light emission [1-3]. Some bacteria also produce accessory fluorescent proteins, which modify the spectral characteristics of the emitted light [4,5]. This probably occurs by transfer of excitation from the primary excited state [6], the flavin-4a-hydroxide [7], to the chromophore of the bound fluorescent protein. An alternative mechanism in which the accessory protein(s) play a direct role in the process of chemiexcitation is also in discussion [8]. However, with bacterial luciferase no other than flavin derivatives have been found to catalyze the emission of light. We report on a molecule, tetrahydro-FMN, which is structurally analogous to FMN but chemically a lumazine (see structures in scheme 1) and which is also capable of light emission.
The present results demonstrate that the bacterial luciferase reaction can proceed in a productive way, i.e. to yield light, also in the absence of the typical flavin moiety. Of course the reactivity of the dihydrolumazine can be assumed to be similar to that of reduced flavin, and indeed the corresponding tetrahydropteridines have been shown to form hydroperoxides which are necessary intermediates during the hydroxylation of aromatic amino acids catalyzed by enzymes such a phenylalanine hydroxylase. We thus assume that the 5,8-dihydrolumazine chromophore bound to luciferase forms a hydroperoxide, which can react with long chain aldehyde in a way similar to that occurring in the normal reaction. The primary function of the flavine/lumazine might thus be to provide a hydroperoxide of appropriate reactivity.