Portland State University. Department of Chemistry.
David H. Peyton
Date of Publication
Master of Science (M.S.) in Chemistry
Hemoproteins, Myoglobin, Nuclear magnetic resonance spectroscopy
1 online resource (2, ix, 73 p.)
NMR studies of paramagnetic hemoproteins have improved significantly our understanding of the structure-function relationship of hemoproteins in general. Up to date most of the studies focus on low-spin ferric systems which are characterized by relatively narrow resonance peaks and concomitant better resolution. However, characterizing in detail the NMR spectra of high-spin ferric hemoproteins is important since there are several hemoproteins, such as peroxidases, catalases, oxygenases, and some ferricytochromes that contain high-spin iron (III) in their biologically active forms. Yet assigning resonances from heme peripheral protons and/or heme pocket residues in high-spin myoglobins is a daunting undertaking. Only a sparse number of active site residues are assigned in such instances, even for metaquo-myoglobin. The protons from the heme and heme pocket residues in high-spin complexes experience extremely fast relaxation and very broad linewidths, which impede the 2D methods that detect through-space and through-bond connectivities. It is the intention of this study to develop an effective strategy to gain more resonance assignments for fast-relaxing protons in hemoproteins. We have set out to use a combined strategy, using two-dimensional exchange spectroscopy (2D-EXSY) with two dimensional nuclear Overhauser effect spectroscopy I correlation spectroscopy I total correlation spectroscopy (NOESY/COSY/TOCSY). I demonstrate here that 2D EXSY experiments can be used to obtain assignment correlations for the heme protons of methydroxy-, metthiocyano-, metaquo-, and metimidazole-myoglobin forms. All these assignments are unambiguous and straightforward. Moreover, saturation-transfer experiments allow determination of ligand binding kinetics. Thus, the exchange rates between the metaquo- and metimidazole- or methyl substituted imidazole myoglobin complexes are estimated. The differences between the exchange rates reflect the differences in the hydrophobic and steric interactions between the ligands and the protein moiety. Although I only demonstrate the feasibility of2D EXSY for the myoglobin case, this assignment strategy should to be applicable to other hemoprotein systems.
Luo, Ying, "Heme Proton Resonance Assignments and Kinetics Study in High-spin and Mixed-spin Metmyoglobin Complexes by Chemical Exchange NMR Spectroscopy" (1996). Dissertations and Theses. Paper 5238.