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Proc Natl Acad Sci U S A. 2015 Oct 20;112(42):12922-7. doi: 10.1073/pnas.1424446112. Epub 2015 Oct 5.

NO binding kinetics in myoglobin investigated by picosecond Fe K-edge absorption spectroscopy.

Author information

1
Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide and Lausanne Centre for Ultrafast Science (LACUS), Institut des Sciences et Ingeniérie Chimiques (ISIC), CH-1015 Lausanne, Switzerland;
2
Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide and Lausanne Centre for Ultrafast Science (LACUS), Institut des Sciences et Ingeniérie Chimiques (ISIC), CH-1015 Lausanne, Switzerland; SwissFEL, Paul Scherrer Institut, CH-5232 Villigen, Switzerland;
3
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
4
SwissFEL, Paul Scherrer Institut, CH-5232 Villigen, Switzerland;
5
Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide and Lausanne Centre for Ultrafast Science (LACUS), Institut des Sciences et Ingeniérie Chimiques (ISIC), CH-1015 Lausanne, Switzerland; majed.chergui@epfl.ch.

Abstract

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 ∼ 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.

KEYWORDS:

X-ray absorption; ligand binding; nitrosylmyoglobin; picosecond; pump–probe

PMID:
26438842
PMCID:
PMC4620891
DOI:
10.1073/pnas.1424446112
[Indexed for MEDLINE]
Free PMC Article

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