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 C 17 O- and 13 CO-Labeled Species

Ki Deok Park, Kermin Guo, Foluso Adebodun, Mark L. Chiu, Stephen G. Sligar, Eric Oldfield

Research output: Contribution to journalArticle

Abstract

We have obtained the oxygen-17 nuclear magnetic resonance (NMR) spectra of a variety of C l7 O-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 17 O NMR chemical shifts, δ i , and spin-lattice relaxation times, T 1 . We have also obtained similar results on a picket fence prophyrin, [5, 10, 15, 20-tetrakis(α,α,α,α-pivalamidophenyl)porphyrinato]iron(II) (l-Melm)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 δ i , between μ(C–O) and the ,7 O nuclear quadrupole coupling constant (e 2 qQ/h, derived from T 1 ), and as expected between e 2 qQ/h and δ i . Taken together with the work of others on the 13 C NMR of 13 CO-labeled proteins, where we find an excellent correlation between δ i ( 13 C) 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 π-back-bonding from Fe d to CO π* 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.

Original languageEnglish (US)
Pages (from-to)2333-2347
Number of pages15
JournalBiochemistry
Volume30
Issue number9
DOIs
StatePublished - Mar 1 1991

ASJC Scopus subject areas

  • Biochemistry

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