A high‐resolution proton nuclear‐magnetic‐resonance investigation of carp hemoglobin

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Abstract
The high-resolution proton NMR spectra of carp Hb were compared to those of human normal adult Hb. Carp deoxy and HbCO in the deoxy-type quaternary state exhibit 2 downfield exchangeable proton resonances as compared to 4 seen in human normal adult deoxyhemoglobin. Two of the hydrogen bonds present in human normal adult deoxyhemoglobin are absent or occur in very different environments in carp Hb. One of the exchangeable proton resonances of carp Hb, while present in the deoxy-type quaternary state of the carbonmonoxy and deoxy derivatives, is absent in the oxy-type quaternary state of both, in agreement with the assignments of these quaternary structures by other methods. The ring-current-shifted proton resonances (sensitive tertiary structural markers) of carp HbCO are substantially different from those of human normal adult Hb. The aromatic proton resonance region of carp Hb has fewer resonances than that of human normal adult Hb, consistent with its much reduced histidine content. The hyperfine-shifted proximal histidyl NH-exchangeable proton resonances of carp HB suggest that during the transition from the oxy to the deoxy quaternary structure, there is a greater alteration in the heme pocket of 1 type of subunit (presumably the .beta. chain) than that in the other subunit. There apparently are differences in both tertiary and quaternary structures between carp and human normal adult Hb which could contribute to the great differences in the functional properties between these 2 proteins.