Abstract
Hemoglobin VII (TaVII) is a major component in the larval hemolymph of Tokunagayusurika akamusi, a common midge (Diptera) found in Japan. This protein contains 150 amino-acid residues including the usual distal histidine at position 64. When the aquomet-form was placed in acidic pH range, its Soret peak was considerably blue-shifted and accompanied by a marked decrease in intensity, indicative of the protein being converted into a structure quite similar to that of Aplysia myoglobin lacking the distal histidine residue. The pH-dependent magnetic circular dichroism spectra in the Soret region have also revealed that TaVII hemoglobin is in an equilibrium between a hexacoordinate and a pentacoordinate structure for its ferric heme iron. We attribute this to a transition from an iron-ligated water molecule that is hydrogen-bonded to the distal histidine, to a water-free iron with the histidine swung-out of the heme pocket. Furthermore, this process was described by the involvement of a single dissociable group with pKa = 6.3 in 0.1 M KC1 at 25°C.
Original language | English |
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Pages (from-to) | 306-309 |
Number of pages | 4 |
Journal | Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular |
Volume | 1208 |
Issue number | 2 |
DOIs | |
Publication status | Published - 1994 Oct 19 |
Externally published | Yes |
Keywords
- (Diptera)
- (T. akamusi)
- CD Soret magnetic
- Distal histidine
- Hemoglobin
- Midge larva
- Pentacoordination
ASJC Scopus subject areas
- Biophysics
- Structural Biology
- Biochemistry
- Molecular Biology