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The influence of ligands at the sixth dismal position on the formation of pi-cation radical in horseradish peroxidase (HRP) is determined. The results showed that fluoride accelerates the reaction of HRP with IrCl(sub 6)(super 2-) to form a new product which is a ferric flouride complex with a porphyrin pi-cation radical. Addition of cyanide slows the reaction. The pH dependence of the one-electron reduction potential of the oxidized HRP-fluoride complex was also determined.

X-ray absorption spectroscopy of the heme-iron structures of lignin and manganese peroxidase isoenzymes from the white rot fungus, Phanerochaete chrysosporium, reveals differences in the atoms of the second and third shell. The data from the second shell indicate H4, H8 and H10 isoenzymes form a group, while the H3 and H5 form another group but the H2 is separate from both the groups. The differences in the shells are probably related to variations in heme conformations.

X-ray absorption fine structure spectroscopy was used in studying the mative lactoperoxidase (LPO), compound II, and the reduced forms at pH6 and pH9. Similarities and differences in the heme-active structures of several peroxidases including horseradish peroxidase, cytochrome c peroxidase, catalase and lignin peroxidase were determined. In addition, changes in spin state were not observed at the different pH values.

The active site of the heme peroxidase horseradish peroxidase (HRP) compound II at pH 7 and pH 10 was investigated using X-ray absorption spectroscopy. The aim was to further characterize the catalytic reaction center of HRP. The results showed that at pH 10, there was a decrease in the Fe-O bond length of HRP compound II. This was attributed to the loss of a hydrogen bond between the oxygen ligand and an amino acid in the heme pocket at higher pH.

Research was conducted on the structure of the active site of lignin peroxidase isozyme H2 using x-ray absorption spectroscopy. The iron content of the native enzyme, the reduced enzyme and compound III of the glycosylated protein was analyzed. Fe-pyrrole nitrogen, Fe-proximal nitrogen and Fe-distal ligand distances were determined. The active-site structure of compound III among the distances was also identified.