TY - JOUR
T1 - Structural characterization of oxidized dimeric Scapharca inaequivalvis hemoglobin by resonance Raman spectroscopy
AU - Boffi, Alberto
AU - Takahashi, Satoshi
AU - Spagnuolo, Carla
AU - Rousseau, Denis L.
AU - Chiancone, Emilia
N1 - Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.
PY - 1994/8/12
Y1 - 1994/8/12
N2 - Resonance Raman spectra of the ferric homodimeric hemoglobin from Scapharca inaequivalvis have been measured over the pH range 5.8-8.3 in buffers of ionic strengths 0.01 and 0.1 M to determine the spin and coordination state of the iron atom. Three species contribute to the spectra: a low spin hexacoordinate, a high spin pentacoordinate, and a high spin hexacoordinate component. Optical absorption and EPR spectra measured under the same conditions allowed the identification of the ligands in the sixth coordination position, namely the distal histidine in the low spin derivative and a water molecule in the high spin one. The relative concentrations of these three species depend on pH in an unusual way. Thus, the aquomet derivative is present over the whole pH range, albeit in small amounts as most of the hemoglobin converts to the low spin hemichrome at acid pH values and to the pentacoordinate derivative at neutral and slightly alkaline ones. The formation of a pentacoordinate heme as the pH is increased has not been reported previously for other myoglobins and hemoglobins. Low ionic strength and high protein concentration favor the formation of the high spin pentacoordinate species, while at high ionic strength and low protein concentration the low spin hexacoordinate species prevails. Ionization of the iron-bound water molecule occurs at pH ≥ 9.3; accordingly, signals from the hydroxyl derivative were not observed in the Raman spectra over the pH range studied.
AB - Resonance Raman spectra of the ferric homodimeric hemoglobin from Scapharca inaequivalvis have been measured over the pH range 5.8-8.3 in buffers of ionic strengths 0.01 and 0.1 M to determine the spin and coordination state of the iron atom. Three species contribute to the spectra: a low spin hexacoordinate, a high spin pentacoordinate, and a high spin hexacoordinate component. Optical absorption and EPR spectra measured under the same conditions allowed the identification of the ligands in the sixth coordination position, namely the distal histidine in the low spin derivative and a water molecule in the high spin one. The relative concentrations of these three species depend on pH in an unusual way. Thus, the aquomet derivative is present over the whole pH range, albeit in small amounts as most of the hemoglobin converts to the low spin hemichrome at acid pH values and to the pentacoordinate derivative at neutral and slightly alkaline ones. The formation of a pentacoordinate heme as the pH is increased has not been reported previously for other myoglobins and hemoglobins. Low ionic strength and high protein concentration favor the formation of the high spin pentacoordinate species, while at high ionic strength and low protein concentration the low spin hexacoordinate species prevails. Ionization of the iron-bound water molecule occurs at pH ≥ 9.3; accordingly, signals from the hydroxyl derivative were not observed in the Raman spectra over the pH range studied.
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M3 - Article
C2 - 8051140
AN - SCOPUS:0028096564
SN - 0021-9258
VL - 269
SP - 20437
EP - 20440
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 32
ER -