A study of the horseradish peroxidase catalytic site by FTIR spectroscopy

Vibrational changes in the catalytic site of horseradish peroxidase were investigated by FTIR (Fourier-transform infrared) spectroscopy in the 1000-2500 cm(-1) range. Difference spectra were generated by photolysis of the haemll-CO compound at different pH/pD values. The spectra report on the fine structure around the catalytic site and show vibrational changes of protein backbone, amino acid residues and cofactors. Assignments of the FTIR vibrations can be made based upon known crystal structures, comparisons with absorption frequencies and extinction coefficients of model amino acids and cofactors, effects of H2O/ (H2O)-H-2 exchange and changes of pH/pD. Concomitant with the photolysis of the Co ligand are changes due to haem and protein vibrations, predominant among which are arginine and histidine residue vibrations.