EPR spectroscopy of semi-methemerythrin

Area of Science:

• Biophysics
• Biochemistry
• Spectroscopy

Background:

• Hemerythrin is an oxygen-binding protein containing non-heme iron.
• Semi-met hemerythrin represents a redox state crucial for understanding iron-sulfur cluster chemistry.
• Previous studies have characterized various hemerythrin forms, but detailed EPR analysis of semi-met states is ongoing.

Purpose of the Study:

• To characterize the electron paramagnetic resonance (EPR) spectra of semi-met hemerythrin forms.
• To investigate the stability and potential disproportionation pathways of these semi-met states.
• To compare EPR properties across different hemerythrin species and their adducts.

Main Methods:

• Preparation of semi-met hemerythrin via one-electron reduction of methemerythrin or oxidation of deoxyhemerythrin.
• EPR spectroscopy at liquid helium temperatures.
• Kinetic analysis of spectral changes at room temperature to assess stability.

Main Results:

• EPR spectra of semi-met hemerythrin from Themiste zostericola were obtained, showing distinct g-values.
• These semi-met forms undergo rapid intramolecular disproportionation with a half-life of 5-8 minutes.
• Similar EPR spectra were observed in other hemerythrin forms, though with varying degrees of disproportionation; azide adducts showed resistance to disproportionation.

Conclusions:

• Semi-met hemerythrin exhibits unique EPR spectral characteristics.
• Intramolecular disproportionation is a significant pathway for semi-met hemerythrin instability.
• Structural variations and ligand binding (e.g., azide) influence the stability and EPR properties of hemerythrin redox states.