THE PEROXIDASE REACTION OF HUMAN METHEMOGLOBIN - 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 tyro syl residues in the catalytic process. The ESR spectra of methaemoglob in modified by tetranitromethane showed on the participation of tyrosi ne in the generation of superoxide anion radical. After repeated catal ytic cycles the rapid decreasing of superoxide anion radical content w as observed. This fact indicated, that the generation of superoxide an ion radical is connected with tyrosyl residues. These residues with hi gh probability are the source of the second electron in the peroxidase catalytic process. For the generation of superoxide anion radical dur ing the peroxidase reaction the dissolved oxygen in the reaction mixtu re is necessary. This oxygen is also responsible for tyrosine destruct ion and thus for the decreasing of peroxidase activity of methaemoglob in.