Spectrochemistry of Firefly Bioluminescence

Abstract

The chemical reactions underlying the emission of light in fireflies and other bioluminescent beetles are some of the most thoroughly studied processes by scientists worldwide. Despite these remarkable efforts, fierce academic arguments continue around even some of the most fundamental aspects of the reaction mechanism behind the beetle bioluminescence. In an attempt to reach a consensus, we made an exhaustive search of the available literature and compiled the key discoveries on the fluorescence and chemiluminescence spectrochemistry of the emitting molecule, the firefly oxyluciferin, and its chemical analogues reported over the past 50+ years. The factors that affect the light emission, including intermolecular interactions, solvent polarity, and electronic effects, were analyzed in the context of both the reaction mechanism and the different colors of light emitted by different luciferases. The collective data points toward a combined emission of multiple coexistent forms of oxyluciferin as the most probable explanation for the variation in color of the emitted light. We also highlight realistic research directions to eventually address some of the remaining questions related to firefly bioluminescence. It is our hope that this extensive compilation of data and detailed analysis will not only consolidate the existing body of knowledge on this important phenomenon but will also aid in reaching a wider consensus on some of the mechanistic details of firefly bioluminescence.

A Brighter picALuc Generated Through the Loss of a Salt Bridge Interaction

“…For example, mutational analysis, in combination with the use of different substrates, has enabled the generation of Renilla luciferase (RLuc) variant with a range of emission wavelengths including those that show peak emission in the red region of the spectrum. 10, 11, 12, 13, 14, 15 Additionally, significant efforts have been made towards developing luciferases that show enhanced bioluminescence activity. These include variants that show an increased bioluminescence such as the consensus-based analysis, protein-protein interaction analysis and protease activity sensors 21, 23, 24 , including its application in protein fragment complementation assay for monitoring protein-protein interaction 25, 26, 27…”

The Protein Environment Restricts the Intramolecular Charge Transfer Character of the Luciferine/Luciferase Complex

“…For each of the simulations, a few snapshots were selected and single point QM/MM calculations were performed on top of them to compute the absorption and emission spectra and characterize the electronic states involved. Moreover, and even thought there is still some debate about the emitting specie of the system, 53 it is in general a good approximation to use the OLU mono-anion in its keto form as chromophore in the model since it is the direct product of the bioluminescence reaction and has been found to be one of the emitting species. [72][73][74]…”

The application and trend of ultra-weak photon emission in biology and medicine

“…It is generally accepted that the relaxation of oxyluciferin excited by luciferase enzyme from the excited state to the ground state emits photons and is called bioluminescence (Yeh and Ai, 2019;Adams and Miller, 2020;Wang and Liu, 2021). Only a few species of organisms exhibit bioluminescence due to specific biochemical reactions, such as insects, fish, algae, and fungi (Haddock et al, 2010;Widder, 2010;Al-Handawi et al, 2022). It is, however, important to note that all living organisms (animals, plants, bacteria, fungi, yeasts, humans) continuously emit ultra-weak photons spontaneously without any external stimulation, which is known as ultra-weak bioluminescence, biophoton emission, ultra-weak photon emission, etc.…”