Separate Assays Specific for Ascorbate Peroxidase and Guaiacol Peroxidase and for the Chloroplastic and Cytosolic Isozymes of Ascorbate Peroxidase in Plants

Ascorbate (AsA) peroxidase can be inactivated both by p-chloromercuribenzoate and by the depletion of AsA but guaiacol peroxidases, such as horseradish peroxidase, cannot. The cytosolic isozymes of AsA peroxidase are less sensitive to depletion of AsA than the chloroplastic isozymes, which include stromal [Chen and Asada (1989) Plant Cell Physiol. 30: 987] and thyla-koid-bound [Miyake and Asada (1992) Plant Cell Physiol. 33: 541] enzymes. Exploring these properties, we established simple methods for separate assays of AsA peroxidase and guaiacol peroxidase and of the three isozymes of AsA peroxidase in plant extracts. These methods were used to characterize the guaiacol peroxidases and isozymes of AsA peroxidase in plants and algae.