Catalytic Mechanism of Fatty Acid Photodecarboxylase: On the Detection and Stability of the Initial Carbonyloxy Radical Intermediate |
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Authors: | Alexey Aleksandrov Adeline Bonvalet Pavel Müller Damien Sorigué Fred Beisson Laura Antonucci Xavier Solinas Manuel Joffre Marten H Vos |
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Institution: | 1. LOB, CNRS, INSERM, École Polytechnique, Institut Polytechnique de Paris, 91120 Palaiseau, France;2. Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France;3. Aix-Marseille University, CEA, CNRS, Institute of Biosciences and Biotechnologies, BIAM Cadarache, 13108 Saint-Paul-lez-Durance, France |
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Abstract: | In fatty acid photodecarboxylase (FAP), light-induced formation of the primary radical product RCOO⋅ from fatty acid RCOO− occurs in 300 ps, upon which CO2 is released quasi-immediately. Based on the hypothesis that aliphatic RCOO⋅ (spectroscopically uncharacterized because unstable) absorbs in the red similarly to aromatic carbonyloxy radicals such as 2,6-dichlorobenzoyloxy radical (DCB⋅), much longer-lived linear RCOO⋅ has been suggested recently. We performed quantum chemical reaction pathway and spectral calculations. These calculations are in line with the experimental DCB⋅ decarboxylation dynamics and spectral properties and show that in contrast to DCB⋅, aliphatic RCOO⋅ radicals a) decarboxylate with a very low energetic barrier and on the timescale of a few ps and b) exhibit little red absorption. A time-resolved infrared spectroscopy experiment confirms very rapid, ≪300 ps RCOO⋅ decarboxylation in FAP. We argue that this property is required for the observed high quantum yield of hydrocarbons formation by FAP. |
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Keywords: | photoenzymes ultrafast spectroscopy quantum simulations radicals reaction pathways |
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