Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 42, Pages 12922-12927Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1424446112
Keywords
nitrosylmyoglobin; ligand binding; X-ray absorption; picosecond; pump-probe
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Funding
- Swiss National Science Foundation (NSF) [200021-116394, 200020-127231, 200021-137596]
- National Centre for Competence in Research: Molecular Ultrafast Science and Technology (NCCR:MUST)
- Swiss National Science Foundation (SNF) [200020_127231, 200021_137596] Funding Source: Swiss National Science Foundation (SNF)
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Diatomic ligands in hemoproteins and the way they bind to the active center are central to the protein's function. Using picosecond Fe K-edge X-ray absorption spectroscopy, we probe the NO-heme recombination kinetics with direct sensitivity to the Fe-NO binding after 532-nm photoexcitation of nitrosylmyoglobin ( MbNO) in physiological solutions. The transients at 70 and 300 ps are identical, but they deviate from the difference between the static spectra of deoxymyoglobin and MbNO, showing the formation of an intermediate species. We propose the latter to be a six-coordinated domed species that is populated on a timescale of similar to 200 ps by recombination with NO ligands. This work shows the feasibility of ultrafast pump-probe X-ray spectroscopic studies of proteins in physiological media, delivering insight into the electronic and geometric structure of the active center.
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