Light emission in firefly: a theoretical study
Résumé
The emitting light in fireflies arises from the electronic relaxation of oxyluciferin, an organic compound resulting from the oxidation of the luciferin substrate inside an enzyme called luciferase. The color of the emitted light can be modulated by mutation of the luciferase. We used quantum mechanical/molecular mechanical (QM/MM) methods, implemented in MOLCAS and TINKER, to clarify the relationship between the structure of the system and the color of the emitted light. The use of the complete active space SCF (CASSCF) and the multi-configurational reference second-order perturbation theory (CASPT2) is required to study of the electronic system and the use of molecular mechanics (MM) to take into account the surrounding molecules. Our systematic theoretical investigation of all the possible light emitter structures of firefly shows that the phenolate-keto form of oxyluciferin is responsible for the light emission.a Our theoretical resultsb on the oxyluciferin-luciferase complex shows in agreement with recent experimental observations that the wavelength of the emitted light depends on the polarity of the microenvironment at the phenol/phenolate terminal of the benzothiazole fragment of oxyluciferin. Color modulation can be optained by mutation of the luciferase or the luciferin on the benzothiazole fragment.