Characterization of acetylcholinesterases of acaricide-resistant and susceptible strains of the cattle tick Boophilus microplus (Can.): I. Extraction of the critical component and comparison with enzyme from other sources |
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Authors: | James Nolan H.J. Schnitzerling |
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Affiliation: | Division of Entomology, CSIRO, Long Pocket Laboratories, Indooroopilly, Queensland, Australia 4068 |
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Abstract: | The critical acetylcholinesterase component, that is responsible for the resistance mechanism of decreased sensitivity to the inhibitor in the cattle tick Boophilus microplus (Can.), has been isolated from the organophosphorus-susceptible Yeerongpilly and resistant Biarra and Ridgelands strains. With the substrate acetylthiocholine this enzyme component gave a pH activity profile similar for all strains. Optimal substrate concentration for Ridgelands was 1.73.10?2M compared to 2.70.10?4M for the other strains. Computed Km values were 1.98.10?5M, 3.65.10?5M, and 6.43.10?6M for Yeerongpilly, Biarra, and Ridgelands strains, respectively, while the corresponding Vmax figures were 336, 135, and 21 μmoles acetylthiocholine hydrolyzed per gram of larvae per hour. These results are discussed in relation to the resistance mechanism and compared with similar parameters derived for this enzyme from bovine erythrocytes, the sheep blowfly Lucilia cuprina, and the sheep nematode Trichostrongylus colubtiformis. |
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