title: The interaction of myeloperoxidase with ligands as studied by EPR.
abstract: 1. The reaction of myeloperoxidase with fluoride, chloride and azide has been studied by EPR. 2. Fluoride decreases the rhombicity of the high-spin heme signal of myeloperoxidase and the nuclear spin of the fluoride atom induces a splitting in g parallel of 35 G. This observation demonstrates that fluoride binds as an axial ligand to the heme iron of the enzyme. 3. Addition of chloride to the fluoride-treated enzyme increases the rhombicity of the high-spin heme signal and brings about a disappearance of the splitting at g parallel. The addition of azide to the fluoride-treated enzyme changes the spin state of the heme iron from a high-to a low-spin state (gx = 2.68, gy = 2.22 and gz = 1.80). 4. Upon addition of chloride or fluoride to low-spin azido-myeloperoxidase this compound is converted into the high-spin chlorido- or fluorido-myeloperoxidase. These observations demonstrate that these ligands compete for a binding site at or close to the heme iron of myeloperoxidase.
mesh_terms: D001386:Azides / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005459:Fluorides / Q000378:metabolism*; D006801:Humans; D007962:Leukocytes / Q000201:enzymology; D009195:Peroxidase / Q000097:blood*; D010544:Peroxidases / Q000097:blood*
chemical_list: D001386:Azides; D002712:Chlorides; D010544:Peroxidases; D009195:Peroxidase; D005459:Fluorides