AbstractExtracts of ground seeds from Annona squamosa revealed interesting insecticidal properties. By an activity‐monitored fractionation, different acetogenins, called annonins and annonacin, were determined to be the active components. The investigation of ATP‐levels (at the LT50value) inPlutella xylostellaunder treatment with annonin I and antimycin A revealed values of 1.45 and 1.35 μmole g−1fresh weight respectively, whereas insecticides primarily afecting neurotoxic targets, e.g. cyfluthrin (sodium channels; 2.25 μmole g−1fresh weight) or parathion (acetylcholinesterase; 2.0 μmole g−1fresh weight) did not influence the ATP‐levels significantly (control; 1.98 μmole g−1fresh weight). Further studies on the target site of annonins revealed an inhibitory effect on the NADH‐cytochrome c‐reductase and complex I of insect mitochondria with IC50values of 4–8 nmole mg−1protein and 0.8 μM respectively for annonin I. Similar results were observed for the inhibition of complex I from bovine heart muscle (IC50:<0.1 μM) or Neurospora crassa cells (IC50: 0.3 μM), whereas coupling sites II or III were not afected. Furthermore, annonins did not reveal any direct inhibition of oxidative phosphor
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