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Transfert de ligand dans la cytochrome c oxydase observé par des expériences femtosecondes infrarouge intégrées et résolues spectralement.

Abstract : Dynamic experiments on hemoproteins, in particuliar spectroscopy experiments, are essential to understand how these proteins accomplish their function. In this context, we have employed infrared femtosecond spectroscopy in order to study the transfer of carbon monoxide in cytochrome c oxidase, from the iron to the copper atom of its bimetallic active site. Infrared experiments are sensitive to the CO vibrational frequency changes and enable us to follow directly the dynamics of the CO transfer. This transfer from the iron to the copper atom takes place on a subpicosecond scale, this is why femtosecond resolution is needed. We developped two infrared femtosecond experiments : a spectrally integrated experiment and a spectrally resolved experiment. In the spectrally integrated experiment, we identified a signal due to the heme absorption. This signal was subtracted from the cinetics in order to extract the signal induced by the CO transfer. A caracteristic time of 400 fs was determined for this transfer. In the spectrally resolved experiment, we observed the evolution of the absorption bands of CO. This evolution shows a delay of 200 fs suggesting a ballistic contribution in the CO transfer. The spectrally resolved experiment uses a new technique recently developped in the laboratory for the characterization of the infrared pulse through upconversion. The signal-to-noise ratio and the resolution accessible with this technique enable the acquisition of an ensemble of differential spectra that is sufficient to validate a new filtering procedure for systematic removal of oscillations due to the pump-perturbed polarization artifacts. Molecular dynamic simulations were performed to model the transfer of CO in cytochrome c oxidase, from the iron to the copper atom of its bimetallic site. These simulations are in good agreement with the experimental results and show that the path from the iron to the copper atom is reproducible. This corroborates the presence of a ballistic component in the transfer.
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Johanne Treuffet. Transfert de ligand dans la cytochrome c oxydase observé par des expériences femtosecondes infrarouge intégrées et résolues spectralement.. Autre [q-bio.OT]. Ecole Polytechnique X, 2006. Français. ⟨pastel-00002200⟩

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