The Soret magnetic circular dichroism of ferric high-spin myoglobins. A probe for the distal histidine residue.
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.
Matsuoka
A
A
Biological Institute and Pharmaceutical Institute, Tohoku University, Sendai, Japan.
Kobayashi
N
N
Shikama
K
K
D000818:Animals; D002942:Circular Dichroism; D006639:Histidine / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D009132:Muscles / Q000737:chemistry; D009211:Myoglobin / Q000737:chemistry*; D014907:Whales
D009211:Myoglobin; D006639:Histidine; D007501:Iron