To find a simple criterion for the presence of the distal (E7) histidine residue in myoglobins and hemoglobins, the Soret magnetic‐circular‐dichroic spectra were examined for ferric metmyoglobins from various species. A distinct and symmetric dispersion‐type curve was obtained for myoglobins containing the distal histidine, whereas a relatively weak and unsymmetric pattern was observed for myoglobins lacking this residue, such as those from three kinds of gastropodic sea molluscs, a shark and the African elephant. The magnetic‐circular‐dichroic spectra obtained would thus be a direct reflection of the presence or absence of a water molecule at the sixth coordinate position of the heme iron(III), this axial water ligand being stabilized by hydrogen‐bond formation to the distal histidine residue. On the basis of these Soret magnetic‐circular‐dichroic signals, we also examined the structure of a protozoan myoglobin (or a monomeric hemoglobin) from Paramecium caudatum of particular interest for the evolution of these proteins from protozoa to higher animals.
|Number of pages||5|
|Journal||European Journal of Biochemistry|
|Publication status||Published - 1992 Nov|
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