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Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy
M Levantino1, H T Lemke2, G Schirò3
1Department of Physics and Chemistry, University of Palermo , Viale delle Scienze, 90128 Palermo, Italy.
Abstract:
We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (∼70 fs) relaxation preceding a slower (∼400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix.
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