Abstract
Abstract High resolution proton nuclear magnetic resonance spectra at 220 MHz were obtained for cyanoferrimyoglobins of sperm whale, harbor seal, harbor or common porpoise, California gray whale, and horse. Carboxymethylated derivatives of sperm whale and porpoise cyanoferrimyoglobin were also studied. The positions of the proton resonances of the heme group, which are greatly shifted by hyperfine interactions with the unpaired electron, delineate the electron spin delocalization from the iron to the porphyrin ring. The nuclear magnetic resonance studies indicate that the electronic structure of the heme group is identical in the cyanoferrimyoglobins of the different mammals, even though the amino acid residues at only 119 of the 153 positions of the polypeptide chain are invariant. Chemical modification of the amino acid residues at some positions did not noticeably affect the heme group either. These results indicate that only the amino acid residues in the immediate environment of the porphyrin ring are involved in the heme-polypeptide interactions which were shown in previous studies to have marked effects on the electronic structure of the heme group.
Highlights
Harbor seal (Phoca titdina) ferrimyoglobin was prepared according to the method described by Hapner et al [15]
Alkylation. of Porpoise and Sperm Whale MyoglobinsPreparations of sperm whale ferrimyoglobin in solution and in the crystalline state were treated for a total of 7 days with 0.2 M bromoacetate at pH 6.8 and room temperature, 22-24’, as described in detail previously [1, 13]
In the sperm whale myoglobin derivatives used for -26.1, -17.7, -13.1, and -12.1 ppm (Fig. 2a)
Summary
High resolution proton nuclear magnetic resonance spectra at 220 MHz were obtained for cyanoferrimyoglobins of sperm whale, harbor seal, harbor or common porpoise, California gray whale, and horse. The nuclear magnetic resonance studies indicate that the electronic structure of the heme group is identical in the cyanof errimyoglobins of the different mammals, even though the amino acid residues at only 119 of the 153 positions of the polypeptide chain are invariant. Chemical modification of the amino acid residues at some positions did not noticeably affect the heme group either These results indicate that only the amino acid residues in the immediate environment of the porphyrin ring are involved in the heme-polypeptide interactions which were shown in previous studies to have marked effects on the electronic structure of the heme group. In the proton nuclear magnetic resonance spectra of low spin ferric heme proteins [3,4,5,6,7], the protons of the heme groups are shifted to high and low field positions by hyperfine interactions with the unpaired electron. The NMR spectra of myogIobins modified by alkylation of some of the histidyl residues [1, 13] were compared to those of the native compounds
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