NMR study of haem exchange reaction of native myoglobin and haemoglobin

Abstract A proton NMR study of the haem exchange reactions of native myoglobin and haemoglobin with the various haems revealed that the haem displacement reaction occurs in native haemoproteins as has been detected in the reconstituted haemoproteins. In the presence of an excess amount of the modified haem, protohaem was excluded from a native haemoprotein to yield a reconstituted haemoprotein containing the modified haem, suggesting that the conformational fluctuations in native haemoprotein are large enough to dissociate its haem from the haem crevice. Although the haemoglobin subunits and myoglobin exhibit very similar three‐dimensional structures as revealed by x‐ray diffraction studies, the rates of the haem exchange reactions in myoglobin were larger than those in the haemoglobin β‐subunit. Such differences in the dynamic properties suggest that these haemoproteins have different interactions between the haem and amino acid residues inside the haem pocket.