Emitter as an Intramolecular Probe in a Luciferase Active Center

The distinctive features of firefly luciferase bioluminescence are complex changes in the shape of the spectra and λmax of bioluminescence with varying pH, temperature, and enzyme structure. An analysis of the published data and the authors’ own results leads to the conclusion that the keto–enol tautomerism of the oxyluciferin molecule explains the observed complex spectral changes most reliably. Only one molecule of an electronically excited product is formed in the active center of the enzyme; therefore, the emitter can be considered as an intramolecular probe characterizing the properties of the emitter microenvironment in the active center of the enzyme. The superposition of two or three forms of the emitter, recorded in the bioluminescence spectra, indicates the coexistence of various conformational forms of luciferase, being in dynamic equilibrium in the reaction medium. An analysis of the bioluminescence spectra enables the identification of qualitatively and quantitatively different conformers of the enzyme and their change with varying external conditions and luciferase structure.