Electron paramagnetic resonance study of carp methemoglobin.

Area of Science:

• Biophysics
• Biochemistry

Background:

• Hemoglobin's structure and function are critical for oxygen transport.
• Azidomethemoglobin is a derivative used to study hemoglobin's electronic properties.
• Electron Paramagnetic Resonance (EPR) spectroscopy is a valuable tool for probing the electronic environment of metal ions in proteins.

Purpose of the Study:

• To investigate the pH-dependent behavior of carp azidomethemoglobin using EPR spectroscopy.
• To compare the pH sensitivity of carp azidomethemoglobin with that of human azidomethemoglobin.
• To elucidate the structural and electronic changes occurring in carp hemoglobin at different pH levels.

Main Methods:

• Electron Paramagnetic Resonance (EPR) spectroscopy was employed to analyze azidomethemoglobin derivatives.
• Crystal field analysis was used to determine spin Hamiltonian parameters, including rhombic (V/lambda) and tetragonal (delta/lambda) distortions.
• Comparative studies were conducted at various pH values (alkaline, pH 4.0, pH 6.0) and with different ligands (azide, water, fluoride).

Main Results:

• Carp azidomethemoglobin EPR spectra showed significant pH dependence, while human azidomethemoglobin spectra did not.
• At acidic pH (4.0), carp azidomethemoglobin exhibited altered V/lambda and delta/lambda values, suggesting increased out-of-plane iron displacement and T-state stabilization.
• A small percentage (1.5%) of high-spin species was observed in carp azidomethemoglobin at pH 6.0 and below, unaffected by inositol hexaphosphate or azide.
• Aquo- and fluoroderivatives of carp methemoglobin were insensitive to pH changes.

Conclusions:

• The pH-dependent EPR spectra of carp azidomethemoglobin indicate conformational changes related to protonation.
• High proton concentration stabilizes the T-form of carp azidomethemoglobin, altering the iron atom's position.
• These findings highlight distinct pH-responsive mechanisms in carp hemoglobin compared to human hemoglobin.