The pH-dependent swinging-out of the distal histidine residue in ferric hemoglobin of a midge larva (Tokunagayusurika akamusi)

Kenichi Akiyama, Mitsunori Fukuda, Nagao Kobayashi, Ariki Matsuoka, Keiji Shikama

Research output: Contribution to journalArticle

17 Citations (Scopus)

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 languageEnglish
Pages (from-to)306-309
Number of pages4
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Volume1208
Issue number2
DOIs
Publication statusPublished - 1994 Oct 19

Keywords

  • (Diptera)
  • (T. akamusi)
  • CD Soret magnetic
  • Distal histidine
  • Hemoglobin
  • Midge larva
  • Pentacoordination

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology

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