Characterization of the peroxidase in human eosinophils.

1. Human eosinophils contain a peroxidase that appears to be of the same type as horseradish peroxidase, lactoperoxidase and intestine peroxidase. 2. Electron paramagnetic resonance spectra of human eosinophils show high-spin ferric heme signals with rhombic symmetry (gx = 6.56, gy = 5.31 and gx = 6.33, gy = 5.59) for the heme group. Part of the more rhombic signal is due to catalase, whereas the other part is completely due to the peroxidase. In addition to these high-spin heme compounds a low-spin heme compound is detectable with g values (gx = 3.09, gy = 2.22 and gz = 1.48) characteristic of a bisimidazole heme iron complex. 3. The amount of heme iron derived from the eosinophil peroxidase, determined from electron paramagnetic spectra, is 13.2 X 10(-17) mol/eosinophil. This is in good agreement with the pyridine hemochrome spectra which yield a value of 13.5 X 20(-17) mol heme iron/eosinophil.