Antioxidant enzymes of larvae of the cabbage looper moth, Trichoplusia ni: subcellular distribution and activities of superoxide dismutase, catalase and glutathione reductase.

In the mid-fifth instar larvae of the cabbage looper moth, Trichoplusia ni, the subcellular distribution of total superoxide dismutase was as follows: 3.05 units (70.0%), 0.97 units (22.3%), and 0.33 units (7.6%) mg-1 protein in the mitochondrial, cytosolic and nuclear fractions, respectively. No superoxide dismutase activity was detected in the microsomal fraction. Catalase activity was unusually high and as follows: 283.4 units (47.3%), 150.1 units (25.1%), 142.3 units (23.8%), and 22.9 units (3.8%) mg-1 protein in the mitochondrial, cytosolic, microsomal (containing peroxisomes), and nuclear fractions. No glutathione peroxidase activity was found, but appreciable glutathione reductase activity was detected with broad subcellular distribution as follows: 3.86 units (36.1%), 3.68 units (34.0%), 2.46 units (23.0%), and 0.70 units (6.5%) mg-1 protein in the nuclear, mitochondrial, and cytosolic fractions, respectively. The unusually wide intracellular distribution of catalase in this phytophagous insect is apparently an evolutionary adaptation to the absence of glutathione peroxidase; hence, lack of a glutathione peroxidase-glutathione reductase role in alleviating stress from lipid peroxidation. Catalase working sequentially to superoxide dismutase, may nearly completely prevent the formation of the lipid peroxidizing .OH radical from all intracellular compartments by the destruction of H2O2 which together with O2- is a precursor of .OH.