Research on the anti-oxidative stress system in insects

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The changes of superoxide dismutase (SOD) activity in the onion maggot, Delia antiqua, were investigated in relation to the growth of larvae and its responsiveness to oxidative stress. Specific SOD activity was very high in the newly hatched larvae, but it decreased rapidly when they started feeding a synthetic diet, which is free from plant secondary compounds. By contrast, SOD activity was increased in a few hours after feeding onion pieces or its homogenate. As ethanol extract of onion had no apparent effect on SOD activity, SOD-inducing compound (s) in onion was considered to be produced by tissue injuries, including those caused by insect feeding.SOD of D.antiqua was purified to apparent homogeneity by ammonium sulfate fractionation, followed by anion exchange, hydrophobic interaction and gel filtration chromatographies. Native molecular weight was estimated as 32,000. SDS-PAGE revealed only one subunit of 16,000, indicating SOD is a homodimer. Isoelectric focusing revealed 3 charge isomers of pIs 5.3,5.5 and 5.7. Specific activity of purified SOD was 4250 units/mg protein. A monoclonal antibody (MAb, aSOD2B7) raised against Delia SOD recognized only SOD of the same genus, but another MAb (aSOD1H11) recognized SOD of Drosophila melanogaster as well.