Peroxidase Associated with Higher Plant Mitochondria

The presence of peroxidase in mitochondria from etiolated mung bean hypocotyls and skunk cabbage spadices, suggested by carbon monoxide difference spectra and the spectral response to methyl hydroperoxide, was shown to result from contamination of the isolated mitochondria by a denser particle fraction with high peroxidase activity. The mitochondria themselves have no peroxidatic activity. Analysis of the homogenate of mung bean hypocotyls revealed that over 90% of the peroxidase was soluble, as expected. Sonication of the isolated mitochondria, however, did not remove all the peroxidase from the particulate fraction, indicating that some of this enzyme is tightly bound to a membrane. These results suggest that the peroxidase in plant cells is localized in lysosomes or microbodies, most of which are ruptured on tissue homogenization to give soluble peroxidase, but some of which survive and appear as membrane bound peroxidase.