Abstract
Among all bioluminescent organisms, the firefly is the most famous, with a high luminescent efficiency of 41%, which is widely used in the fields of biotechnology, biomedicine and so on. The entire bioluminescence (BL) process involves a series of complicated in-vivo chemical reactions. The BL is initiated by the enzymatic oxidation of luciferin (LH2). However, the mechanism of the efficient spin-forbidden oxygenation is far from being totally understood. Via MD simulation and QM/MM calculations, this article describes the complete process of oxygenation in real protein. The oxygenation of luciferin is initiated by a single electron transfer from the trivalent anionic LH2 (L3−) to O2 to form 1[L•2−…O2•−]; the entire reaction is carried out along the ground-state potential energy surface to produce the dioxetanone (FDO−) via three transition states and two intermediates. The low energy barriers of the oxygenation reaction and biradical annihilation involved in the reaction explain this spin-forbidden reaction with high efficiency. This study is helpful for understanding the BL initiation of fireflies and the other oxygen-dependent bioluminescent organisms.
Highlights
The firefly is the most efficient bioluminescent system for converting chemical energy into light with the extremely high luminescence efficiency of 41% [1]
Results and Discussion process is accompanied by a small amount of back negative charge transfer (CT) from L2−
This is a spin-forbidden rewith usually a low efficiency, which contradicts the fact that is the most action with usually a low efficiency, which contradicts the the factfirefly that the firefly is effithe cient bioluminescent system for converting chemical energy into light
Summary
The firefly is the most efficient bioluminescent system for converting chemical energy into light with the extremely high luminescence efficiency of 41% [1]. In 2018, an umbrella sampling molecular dynamics simulation and QM/MM study pointed out the approach of the oxygen moving inside the protein and defined the formation of FDO− , but did not provide details along the reaction path [22]. Our group has investigated the oxygenation process in DMSO, and described a complete process with potential energy curves (PECs) of both ground state (S0 ) and triplet state (T1 ) to confirm the SET mechanism [23] The initial structures for complete process with potential energy curves (PECs) of both ground state (S0) and triplet the QM/MM calculations were started at the snapshot of 1800 ps from the MD trajectory state (T1) to confirm(Figure the SET mechanism [23].contains. Between the oxygenation pathway in a solvent and in protein? How does the spin-forbidden reaction of firefly BL occur so efficiently? To answer these three questions is the purpose of this article
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