The solutionmolecular andelectronic structuresof theactive site in the extremelyO2-avidhemoglobin fromthe trematode Paramphistomum epiclitumhave been investigated by 1 H NMR on the cyanomet form in order to elucidate the distal hydrogen-bonding to a ligated H-bond acceptor ligand. Comparison of the strengths of dipolar interactions in solution with the alternate crystal structures of methemo-globin establish that the solution structure of wild-type Hb more closely resembles the crystal structure of the recom-binant wild-type than the true wild-type met-hemoglobin
