Our current research involves the structure-function-reactivity relationships of heme proteins. Hemes and heme proteins are vital components of essentially every cell of almost every living organism. We are investigating both synthetic and natural metal-free porphyrins, iron porphyrins (hemes), iron chlorins, isobacteriochlorins, other related macrocycles, and proteins that contain these. Projects involve gene synthesis and/or cloning, bacterial expression and purification of heme proteins, structures, electron transfer or enzymatic reactions of heme proteins, magnetic properties of cytochromes, structure and electronic properties of nitrosylheme proteins, binding of small molecules to myoglobins and hemoglobins. Techniques that we use include one- and two-dimensional 1H and 13C NMR spectroscopy, metal nucleus NMR spectroscopy, continuous wave and pulsed EPR spectroscopy, electronic, low temperature magnetic circular dichroism, Mössbauer and photoelectron spectroscopies, electrochemistry of model hemes and heme proteins, thermodynamics and kinetics of ligand addition to metal complexes and heme proteins. We are using all of these techniques to investigate the mechanism of action of the reversible NO-carrying proteins from the blood-sucking insect, Rhodnius prolixus (in collaboration with the Montfort research group), the reactivity and mechanism of action of the mitochondrial bc1 complex of yeast.
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Yatsunyk, L.A., A. Dawson, M.D. Carducci, G.S. Nichol, and F.A. Walker. 2006. Models of the cytochromes: crystal structures and EPR spectral characterization of low-spin bis-imidazole complexes of (OETPP)FeIII having intermediate ligand plane dihedral angles. Inorganic Chemistry 45: 5417-5428.
Jacobsen, N.E., K. Kövér, M.B. Murataliev, R. Feyereisen, and F.A. Walker. 2006. Structure and stereochemistry of products of hydroxylation of human steroid hormones by a housefly cytochrome P450 (CYP6A1). Magnetic Resonance in Chemistry 44: 467-474.
Teschner, T., L.A. Yatsunyk, V. Schünemann, H. Paulsen, H. Winkler, C. Hu, W.R. Scheidt, F.A. Walker, and A.X. Trautwein. 2006. Low-spin ferriheme models of the cytochromes: Mössbauer spectra of six crystalline complexes having axial ligand plane dihedral angles ranging from 0degrees to 90 degrees. Journal of the American Chemical Society 128: 1379-1389.
Nardis, S. R. Paolessee, S. Licoccia, F.R. Fronczek, M.G.H. Vicente, and T.Kh. Shokhirevnonplanar iron corrolates: modified patterns of spin delocalization and coupling in slightly saddled chloroiron(III) corrolate radicals. Inorganic Chemistry 44: 7030-7046.
Yatsunyk, L.A., H. Ogura, and F.A. Walker. 2005. Kinetics of ring inversion in strongly non-planar iron(III) octaalkyltetraphenylporphyrinates. Inorganic Chemistry 44: 2867-2881.Yatsunyk, L.A., N.V. Shokhirev, and F.A. Walker. 2005. Magnetic resonance spectroscopic investigations of the electronic ground and excited states in strongly non-planar iron(III) dodecasubstituted porphyrins,”Inorganic Chemistry 44: 2848-2866.
Cai, S., D.L. Lichtenberger, and F.A. Walker. 2005. NMR and EPR studies of the bis-pyridine and bis-t-butylisocyanide complexes of iron(III) octaethylchlorin complexes. Inorganic Chemistry 44: 1890-1903.
Weichsel, A., E.M. Maes, J.F. Andersen, J.G. Valenzuela, T. Kh. Shokhireva, F.A. Walker, and W.R. Montfort. 2005. Heme-assisted nitrosothiolation of a proximal thiol in a nitric oxide transport protein. Proceedings of the National Academy of Sciences U.S.A. 102: 594-599.
Murataliev, M.B., L.N. Trinh, L.V. Moser, R.B. Bates, R. Feyereisen, and F.A. Walker. 2004. Chimeragenesis of the fatty acid binding site of cytochrome P450BM3. Replacement of the residues 73-82 with the homologous residues from the insect cytochrome P450 CYP4C7. Biochemistry 43: 1771-1780.
Shokhireva, T.Kh., N.V. Shokhirev, and F.A. Walker. 2003. Assignment of heme resonances and determination of the electronic structures of high- and low-spin nitrophorin 2 by 1H and 13C NMR spectroscopy: An explanation of the order of heme methyl resonances in high-spin ferriheme proteins. Biochemistry 42: 679-693.
Shokhireva, T.Kh., R.E. Berry, E. Uno, C.A. Balfour, H. Zhang, and F.A. Walker. 2003. Electrochemical and NMR spectroscopic studies of distal pocket mutants of nitrophorin 2: stability, structure, and dynamics of axial ligand complexes. Proceedings of the National Academy of Sciences U.S.A. 100: 3778-3783.
Berry, R.E., X.D. Ding, T.Kh. Shokhireva, A. Weichsel, W.R. Montfort, and F.A. Walker. 2004. Axial ligand complexes of the Rhodnius nitrophorins: reduction potentials, binding constants, EPR spectra, and structures of the 4-iodopyrazole and imidazole complexes of NP4. Journal of Biological Inorganic Chemistry 9: 135-144.
