| Summary: | 1H-NMR spectra of deoxy myoglobins (Mbs) from shark ( Galeorhinus japonicus ), horse, and sperm whale have been studied to gain insights into their active site structure. It has been demonstrated for the first time that nuclear Overhauser effect (NOE) can be observed between heme peripheral side-chain proton resonances of these paramagnetic complexes. Val-Ell methyl and His-F8 C 8 H proton resonances of these Mbs were also assigned from the characteristic shift and line width. The hyperfine shift of the former resonance was used to calculate the magnetic anisotropy of the protein. The shift analysis of the latter resonance, together with the previously assigned His-F8 N δ H proton resonance, revealed that the strain on the Fe-N e bond is in the order horse Mb∼whale Mb <shark Mb and that the hydrogen bond strength of the His-F8 N δ H proton to the main-chain carbonyl oxygen in the preceding turn of the F helix is in the order shark Mb <horse Mb <whale Mb. Weaker Fe-N δ porphyrin interaction in shark Mb was manifested in a smaller shift of the heme methyl proton resonance and appears to result from distortion of the coordination geometry in this Mb. Larger strain on the Fe-Ne bond in shark Mb should be to some extent attributed to its lowered 02 affiuiity (P 50 =1.1 mmHg at 20°C), compared to whale and horse Mbs.
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