Biochemical and toxicological studies on acetyl cholinesterase from larvae of red palm weevil (Rhynchophorous ferrugineus) / Sarah Adel Abdelghany Aboelenin ; Supervised Shebl Abdel Monem Shalaan , Magda Abdel Naby Mohamed , Atef Abdel Moneam Ali

Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Zoology

Red palm weevil (RPW), Rhynchophorus ferrugineus, is the most destructive pest of many palm trees. The synthetic insecticides are the main strategy for control. Distribution of acetylcholinesterase (AChE), as a detoxifying enzyme and the target site of inhibition by insecticides, in different organs of the 10th instar larvae of the pest including whole gut, cuticle, fat body, head and haemolymph was estimated. The activity ranged from 314.9 to 3868 U/organ with specific activity ranged from 99 to 340.8 U/mg proteins where the cuticle had the highest enzyme level. The enzyme activity was tracked in cuticles during larval development; the11th instar larvae had the highest enzyme content with 5630 U/cuticle with specific activity 140 U/mg proteins. Two major AChE isoenzymes, AChEIIb and AChEIIIb, were purified by chromatography on ion exchange and gel filtration columns. The two isoenzymes AChEIIb and AChEIIIb had specific activities of 3504.3 and 2979 U/mg protein, molecular weights of 33 and 54 kDa, activation energies of 8.3 and 4.4 kCal/mol, respectively.Both isoenzymes had monomeric forms, optimum activity at pH 8.0 and 40o C, completely inhibited by Hg2+ and Cu2, similar trends towards the inhibitors eserine, BW284C51 and iso-OMPA. The sensitivity of R. ferrugineus AChEIIb and AChEIIIb in vitro towards six different insecticides was investigated. The insecticides belong to four different classes including organophosphates (OPs) (chloropyrifos and malathion), carbamates (oxamyl, carbosulfan), pyrethroid (deltamethrin) and avermectin (emamectinbenzoate)

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