title: Distal and proximal ligand interactions in heme proteins: correlations between C-O and Fe-C vibrational frequencies, oxygen-17 and carbon-13 nuclear magnetic resonance chemical shifts, and oxygen-17 nuclear quadrupole coupling constants in C17O- and 13CO-labeled species.
abstract: We have obtained the oxygen-17 nuclear magnetic resonance (NMR) spectra of a variety of C17O-labeled heme proteins, including sperm whale (Physeter catodon) myoglobin, two synthetic sperm whale myoglobin mutants (His E7----Val E7; His E7----Phe E7), adult human hemoglobin, rabbit (Oryctolagus cuniculus) hemoglobin, horseradish (Cochlearia armoracia) peroxidase (E.C. 1.11.1.7) isoenzymes A and C, and Caldariomyces fumago chloroperoxidase (E.C. 1.11.1.10), in some cases as a function of pH, and have determined their isotropic 17O NMR chemical shifts, delta i, and spin-lattice relaxation times, T1. We have also obtained similar results on a picket fence prophyrin, [5,10,15,20-tetrakis(alpha, alpha, alpha, alpha, alpha-pivalamidophenyl)porphyrinato]iron(II) (1-MeIm)CO, both in solution and in the solid state. Our results show an excellent correlation between the infrared C-O vibrational frequencies, v(C-O), and delta i, between v(C-O) and the 17O nuclear quadrupole coupling constant (e2qQ/h, derived from T1), and as expected between e2qQ/h and delta i. Taken together with the work of others on the 13C NMR of 13CO-labeled proteins, where we find an excellent correlation between delta i(13C) and v(Fe-C), our results suggest that IR and NMR measurements reflect the same interaction, which is thought to be primarily the degree of pi-back-bonding from Fe d to CO pi* orbitals, as outlined previously [Li, X.-Y., & Spiro, T.G. (1988) J. Am. Chem. Soc. 110, 6024]. The modulation of this interaction by the local charge field of the distal heme residue (histidine, glutamine, arginine, and possibly lysine) in a variety of species and mutants, as reflected in the NMR and IR measurements, is discussed, as is the effect of cysteine as the proximal heme ligand.
authors.affiliation: School of Chemical Sciences, University of Illinois, Urbana-Champaign 61801.
authors.forename: K D
authors.initials: KD
authors.lastname: Park
authors.forename: K M
authors.initials: KM
authors.lastname: Guo
authors.forename: F
authors.initials: F
authors.lastname: Adebodun
authors.forename: M L
authors.initials: ML
authors.lastname: Chiu
authors.forename: S G
authors.initials: SG
authors.lastname: Sligar
authors.forename: E
authors.initials: E
authors.lastname: Oldfield
mesh_terms: D002247:Carbon Isotopes; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism; D007501:Iron; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008433:Mathematics; D008962:Models, Theoretical; D009211:Myoglobin / Q000737:chemistry; D010103:Oxygen Isotopes; D011485:Protein Binding; D013816:Thermodynamics; D014732:Vibration
chemical_list: D002247:Carbon Isotopes; D006420:Hemeproteins; D008024:Ligands; D009211:Myoglobin; D010103:Oxygen Isotopes; D007501:Iron