| Summary: | ABSTRACT: W e have obtained the oxygen-17 nuclear magnetic resonance ( N M R) spectra of a variety of CI70-labeled heme proteins, including sperm whale (Physeter cutodon) myoglobin, two synthetic sperm whale myoglobin mutants (His E7- Val E7; His E7- Phe E7), adult human hemoglobin, rabbit (Or-yctolagus cuniculus) hemoglobin, horseradish (Cochlearia armoracia) peroxidase (E.C. 1.1 1.1.7) isoenzymes A and C, and Culduriomyces fumago chloroperoxidase (E.C. 1.1 1.1. lo), in some cases as a function of pH, and have determined their isotropic I7O N M R chemical shifts, ai, and spin-lattice relaxation times, T I. W e have also obtained similar results on a picket fence prophyrin, [ 5,10,15,20-tetrakis(a,a,a,a-pivalamido-phenyl)porphyrinato]iron(lI) ( l-MeIm)CO, both in solution and in the solid state. Our results show an excellent correlation between the infrared C- 0 vibrational frequencies, v(C-0), and ai, between u(C-0) and the I7O nuclear quadrupole coupling constant ($qQ/h, derived from T I) , and as expected between $qQ/h and ai. Taken together with the work of others on the I3C N M R of I3CO-labeled proteins, where we find an excellent correlation between Bi(13C) and u(Fe-C), our results suggest that I R and N M R measurements reflect the same interaction, which is thought to be primarily the degree of n-back-bonding from Fe d to
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