ASCORBATE PEROXIDASE - A NOVEL ANTIOXIDANT ENZYME IN INSECTS

Ascorbate peroxidase (APOX) activity, which catalyzes the oxidation of ascorbic acid with the concurrent reduction of hydrogen peroxide (H2O 2), was found in larvae of Helicoverpa tea. Since insects apparently l ack a Se-dependent glutathione peroxidase and since catalase has a low affinity for H2O2, this enzyme may be important in removing H2O2 in i nsects. We partially purified the APOX activity 58x from the whole bod y homogenates and investigated its activity with model lipid peroxides , electron donors, and known inhibitors of plant APOX. The H. tea APOX has activity with model lipid peroxides. This, along with the APOX ac tivity found in fat body tissues, suggests that ascorbate peroxidase m ay be important in removing lipid peroxides in insects. The H. tea APO X has broader specificity for electron donors than the plant APOX with activity using cysteine, NADPH, glutathione, and cytochrome C as elec tron donors (22-93% of activity with ascorbate). The H. tea APOX is al so resistant to many of the known inhibitors of plant APOX, suggesting that the enzyme has a different active site and may not be a heme-per oxidase. (C) 1997 Wiley-Liss, Inc.