The Peroxidase Reaction of Human Methaemoglobin: Character of the Amino Acid Electrondonor and the Influence of Oxygen

The chemical modification of tyrosyl residues in methaemoglobin led to the decreased peroxidase activity and thus confirmed the role of tyrosyl residues in the catalytic process. The ESR spectra of methaemoglobin modified by tetranitromethane showed on the participation of tyrosine in the generation of superoxide anion radical. After repeated catalytic cycles the rapid decreasing of superoxide anion radical content was observed. This fact indicated, that the generation generation of superoxide anion radical is connected with tyrosyl residue. The residues with high probability are the source of the second electron in the peroxidase reaction the dissolved oxygen in the reaction mixture is necessary. This oxygen is also responsible for tyrosine destruction and thus for the decreasing of peroxidase activity of methaemoglobin.