ИСТИНА

Investigation of the firefly bioluminescence spectra and the emitter structure is one of the important problems already in the first researches on the reaction mechanism. The studies of natural and model bioluminescent systems showed that bioluminescence of firefly luciferases is characterized by complex changes of the emission spectra and bioluminescence λmax occurring with changing pH, temperature, and the enzyme structure. The firefly bioluminescence maximum in nature varied in a wide range. So, the conclusion was made that the bioluminescence spectra were defined by microenvironment of the emitter in the enzyme active center. Already at the start of 21st century substantial experimental evidence has been accumulated corroborating contribution of the keto-enol tautomerization mechanism to the firefly bioluminescence. The numerous experimental results suggested that the red emission is related to the keto-form, while the yellow-green emission – to the enol/enolate form of the emitter. Despite the large number of publications considering the structure of bioluminescence emitter based on keto-enol tautomerization, several authors suggested alternative hypothesis on the emitter structure: 1) the keto-form of oxyluciferin is the only emitter in this system, which could exist as two stereo-conformations with the planar (green emitter) and perpendicular (red emitter) mutual arrangement of the benzothiazole and thiazole rings; 2) the different resonance structures of the oxyluciferin keto-anion generate green and red bioluminescence; 3) the entire variety of the firefly bioluminescence spectra theoretically is explained by polarization of the OH-bond in the protein microenvironment in any form of the emitter; 4) the spectrum of enolate ion can cover the entire range of yellow-green and red bioluminescence. However, novel experimental evidence for existence of keto-enol tautomerzation of oxyluciferin in solution and in complex with luciferase appeared in the literature and the results of our own research allowed concluding that keto-enol tautomerization of the excited oxyluciferin molecule provides the most adequate explanation of the observed complex spectral changes.