High-field, variable-temperature Mössbauer effect measurements on oxyhemeproteins.

Area of Science:

• Biophysics
• Biochemistry
• Spectroscopy

Background:

• Oxyhemeproteins like hemoglobin and myoglobin are crucial for oxygen transport.
• The electronic state of the heme iron in these proteins is fundamental to their function.
• Previous studies suggested an excited triplet state in oxyhemoglobin, but experimental evidence was lacking.

Purpose of the Study:

• To investigate the electronic state of the oxyheme complex in human oxyhemoglobin, its beta chains, and oxymyoglobin.
• To determine if an excited triplet state exists in these oxyhemeproteins.
• To provide a detailed characterization of the oxyheme electronic structure.

Main Methods:

• Mössbauer spectroscopy was employed to analyze human oxyhemoglobin, isolated beta chains, and horse/sperm whale oxymyoglobin.
• Measurements were conducted under varying magnetic fields (4 or 6 T) and temperatures (4.2–200 K).
• Diamagnetic sodium nitroprusside was used as a control, and spectral data were modeled using adjustable parameters.

Main Results:

• Mössbauer spectra were adequately reproduced by a model assuming diamagnetic iron.
• The analysis included quadrupole splitting, asymmetry parameter, and Mössbauer linewidth as adjustable parameters.
• No evidence supporting the existence of an excited triplet state in oxyhemeproteins was found.

Conclusions:

• The iron in the oxyheme complex of the studied proteins is predominantly diamagnetic.
• The findings contradict previous hypotheses of an excited triplet state in oxyhemoglobin.
• Mössbauer spectroscopy provides a robust method for characterizing the electronic state of heme iron.