Complementary Mössbauer and EPR Studies of Iron(III) in Diferric Human Serum Transferrin with Oxalate or Bicarbonate as Synergistic Anions

A. Seidel, E. Bill, L. Haggstrom, P. Nordblad, F. Kilár

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Abstract

The spectral and magnetic properties of iron(III) bound in the metal binding sites of human serum transferrin with oxalate or bicarbonate as synergistic anions has been studied with Mössbauer spectroscopy and electron paramagnetic resonance (EPR). The Mössbauer spectra of the iron(III) in diferric transferrin with oxalate have been described using a spin Hamiltonian with the values of the zero field splitting parameter, D = 0.55 ± 0.05 cm-1, and the rhombicity of the crystal field, E/D = 0.045 ± 0.005. The EPR spectrum can be described with D = 0.58 cm-1 and E/D = 0.057, using a g-strain model for the lineshape that is based on a Gaussian distribution of D and E/D with Gaussian widths σ(D) = 0.35 cm-1 and σ(E/D) = 0.013, respectively. The rhombicity of the iron surroundings for the transferrin-oxalate complex is almost one order of magnitude smaller than for the bicarbonate complex and the zero field splitting parameter is twice as large in the oxalate as in the bicarbonate complex. We conclude that the crystal field symmetry of the iron site is almost tetragonal in the oxalate complex but rhombohedral in the bicarbonate complex, reflecting the different geometries of the oxalate and bicarbonate coordination. The isomer shift δ = 0.56 ± 0.01 mm s-1 and the quadrupole splitting ΔEQ = 0.2 ± 0.1 mm s-1, on the other hand, are very close to the values found for the bicarbonate complex. No differences between the Mössbauer spectra of the two iron(III) ions in diferric transferrin with oxalate were found. The homogeneity of the diferric transferrin samples was controlled by capillary zone electrophoresis in the presence of urea.

Original languageEnglish
Pages (from-to)52-63
Number of pages12
JournalArchives of Biochemistry and Biophysics
Volume308
Issue number1
DOIs
Publication statusPublished - Jan 1994

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Oxalates
Electron Spin Resonance Spectroscopy
Transferrin
Bicarbonates
Anions
Paramagnetic resonance
Iron
Serum
Hamiltonians
Crystals
Normal Distribution
Gaussian distribution
Capillary Electrophoresis
Crystal symmetry
Electrophoresis
Isomers
Urea
Spectrum Analysis
Magnetic properties
Metals

ASJC Scopus subject areas

  • Molecular Biology
  • Biophysics
  • Biochemistry

Cite this

Complementary Mössbauer and EPR Studies of Iron(III) in Diferric Human Serum Transferrin with Oxalate or Bicarbonate as Synergistic Anions. / Seidel, A.; Bill, E.; Haggstrom, L.; Nordblad, P.; Kilár, F.

In: Archives of Biochemistry and Biophysics, Vol. 308, No. 1, 01.1994, p. 52-63.

Research output: Contribution to journalArticle

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abstract = "The spectral and magnetic properties of iron(III) bound in the metal binding sites of human serum transferrin with oxalate or bicarbonate as synergistic anions has been studied with M{\"o}ssbauer spectroscopy and electron paramagnetic resonance (EPR). The M{\"o}ssbauer spectra of the iron(III) in diferric transferrin with oxalate have been described using a spin Hamiltonian with the values of the zero field splitting parameter, D = 0.55 ± 0.05 cm-1, and the rhombicity of the crystal field, E/D = 0.045 ± 0.005. The EPR spectrum can be described with D = 0.58 cm-1 and E/D = 0.057, using a g-strain model for the lineshape that is based on a Gaussian distribution of D and E/D with Gaussian widths σ(D) = 0.35 cm-1 and σ(E/D) = 0.013, respectively. The rhombicity of the iron surroundings for the transferrin-oxalate complex is almost one order of magnitude smaller than for the bicarbonate complex and the zero field splitting parameter is twice as large in the oxalate as in the bicarbonate complex. We conclude that the crystal field symmetry of the iron site is almost tetragonal in the oxalate complex but rhombohedral in the bicarbonate complex, reflecting the different geometries of the oxalate and bicarbonate coordination. The isomer shift δ = 0.56 ± 0.01 mm s-1 and the quadrupole splitting ΔEQ = 0.2 ± 0.1 mm s-1, on the other hand, are very close to the values found for the bicarbonate complex. No differences between the M{\"o}ssbauer spectra of the two iron(III) ions in diferric transferrin with oxalate were found. The homogeneity of the diferric transferrin samples was controlled by capillary zone electrophoresis in the presence of urea.",
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