The role of energy transfer in bioluminescence quenching by xanthene dyes.

The paper reports the experimental results of bioluminescence quenching in the coupled enzyme system NADH:FMN-oxidoreductase-luciferase in the presence of xanthene dyes (fluorescein, eosin Y, erythrosin B) featured by the rate constants of intersystem crossing. From the spectral data and with the help of kinetic model the rate constants of energy transfer from emitter to dye were determined (2.9 x 10(12)-6.5 x 10(13) M(-1) s(-1)) and the emitter lifetime was estimated (1.2-2.7 ns). The calculated rate constants of energy transfer in a series of xanthene molecules are higher than the diffusion-controlled constants. The rate constants of energy transfer correlate with the probability of intersystem crossing of a dye. The combined analysis of emitter fluorescence quenching and acceptor fluorescence enhancement indicates that the significant bioluminescence intensity decrease in the presence of xanthene dyes is determined by both the quenching processes via the energy transfer and the inhibition of bioluminescent reaction.

Estimation of energy of the upper electron-excited states of the bacterial bioluminescent emitter.

The hypothesis of activity of the upper electron-excited states of the bacterial bioluminescent emitter was verified using dye molecules as foreign energy acceptors. Six compounds were selected having fluorescent state energies ranging from 25,700 to 32,000 cm(-1) (anthracene, pyrene, 1.4-bis(5-phenyloxasol-2-yl)benzene (POPOP), p-bis(o-methylstyryl)benzene (MSB), 2-methoxy-naphtalene, p-terphenyl), exceeding that of the bioluminescent emitter (22,000 cm(-1)). Their absorption spectra do not overlap with the bioluminescence spectrum; the trivial light absorption and the intermolecular resonance S-S energy transfer were excluded. Bacterial bioluminescent spectra of the coupled enzyme system NADH:FMN-oxidoreductase-luciferase in the presence of MSB were presented as an example. The weak sensitized fluorescence of MSB was registered. The results obtained have confirmed the activity of the energetic precursor in the bacterial bioluminescence. Its energy can be located in the interval of 26,000-27,000 cm(-1).

Upper electron-excited states in bioluminescence: experimental indication.

The involvement of upper electron-excited states in bacterial bioluminescence process was studied with excitation energy-accepting molecules. The fluorescent aromatic compounds, anthracene and 1.4-bis(5-phenyloxazol-2-yl)benzene, were chosen. Energies of their lowest excited singlet states are higher than the energy of the analogous state of the bioluminescence emitter; their absorption spectra and bioluminescence do not overlap. Hence, the excitation of these molecules by singlet-singlet energy transfer or by light absorption is excluded. Sensitized fluorescence of these compounds in the bioluminescence systems has been recorded, indicating the activity of upper electron-excited states in the bioluminescent process.