Multinuclear NMR Studies of Hemoproteins and Their Model Compounds
Lee, Hee Cheon
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https://hdl.handle.net/2142/70413
Description
Title
Multinuclear NMR Studies of Hemoproteins and Their Model Compounds
Author(s)
Lee, Hee Cheon
Issue Date
1988
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Abstract
Nuclear magnetic resonance (NMR) in both solution and solid state has been used to study the active site structure of various hemoproteins, and the nature of the iron-oxygen bond in oxyhemoglobin. The first iron-57 NMR spectra of a metalloprotein, carbonmonoxymyoglobin, has been obtained, yielding the isotropic chemical shift, the anisotropy of the chemical shielding tensor and the rotational correlation time of the protein. The oxygen-17 NMR signals from CO ligands bound to oxygen-transport hemoproteins are much narrower than expected, and the lineshape is non-Lorentzian. The results indicate that the unusual linewidths and lineshapes originate from the multiexponential nature of quadrupolar relaxation outside of the extreme narrowing limit, permitting determinations of the oxygen-l7 nuclear quadrupole coupling constants and the rotational correlation time of the proteins. A correlation between the oxygen-l7 chemical shift and the CO binding affinity of the protein has been found. Oxygen-17 NMR studies of various carbonmonoxy peroxidases demonstrated that the peroxidases exist in two distinct states, which undergo reversible acid-base induced transitions characterized by a single pK value. Finally, the nature of the iron-oxygen bond in the heme model compound, $\sp $O$\sb2$-picket fence porphyrin, has been probed by the use of solid state oxygen-17 NMR. The results demonstrated that the oxygen-l7 chemical shifts of both the terminal and bridging oxygen atoms are unusually shifted to the downfield with very large chemical shift anisotropies, and that the dioxygen rotates fast around the iron-oxygen axis at room temperature. The principal components of the shielding tensors for both oxygens have been determined.
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