Metal ion environment in reconstituted hemoglobins and myoglobins

Studies on reconstituted hemeproteins, viz, hemoglobin and myoglobin, with metal ions such as Co(II), Ni(II) and Cu(II), using a variety of spectroscopic techniques such as EPR, NMR, resonance Raman and optical, indicate three levels at which the metal ion coordinations are influenced by protein conformation. While in monomeric proteins the type of coordination, essentially a five-coordinate one, is determined by the protein conformation in the heme pocket, the sub-unit interactions in tetrameric proteins can produce a mixture of two types of coordination in individual proteins, one similar to that in monomeric proteins and the other a four-coordinate one with a possible weak axial coordination. As a result, tetrameric proteins with Ni(II) as the metal ion reveal the presence of differing spin states. Furthermore, it is proved that the effects on the proximal histidine associated with the R and T quaternary conformation influence the five-coordinated sites. Some results on hybrid hemoglobins as well as those from isolated chains are also reported. © 1990 Indian Academy of Sciences.