Axial ligand coordination in intestinal peroxidase

Area of Science:

• Biochemistry
• Biophysics
• Enzymology

Background:

• Peroxidases are crucial enzymes involved in various biological processes.
• Understanding the heme environment and ligand interactions is key to elucidating enzyme function.
• Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful tool for studying paramagnetic species like heme proteins.

Purpose of the Study:

• To characterize the EPR spectra of intestinal peroxidase for the first time.
• To compare the heme environment and spectral properties of intestinal peroxidase with lactoperoxidase.
• To investigate the influence of pH and chloride ions on enzyme forms and the role of proximal histidine ligands.

Main Methods:

• Electron Paramagnetic Resonance (EPR) spectroscopy was employed to analyze resting and cyanide-ligated states of intestinal and lactoperoxidase.
• Spectra were recorded under varying pH conditions and in the presence of chloride ions.
• Comparison of g-values and spectral features with other hemeproteins of known structure.

Main Results:

• Intestinal peroxidase exhibits a pH-dependent high spin EPR spectrum, with chloride shifting the acidic/neutral equilibrium.
• Resting lactoperoxidase shows both low and high spin species, indicating a different heme environment than intestinal peroxidase.
• Cyanide adducts of both peroxidases display similar g-values, suggesting conserved proximal histidine ligation.

Conclusions:

• The study provides the first EPR characterization of intestinal peroxidase, highlighting its unique spectral properties.
• Differences in resting spectra suggest distinct heme environments between intestinal and lactoperoxidase.
• EPR analysis of cyanide complexes supports the role of histidine as the proximal ligand in mammalian peroxidases.