Insecticidal properties of natural products may present alternatives to the use of synthetic molecule pesticides that are of diminishing effectiveness due to resistance. Three compounds, thymoquinone, nootkatone, and carvacrol, components of Alaska yellow cedar, Chamaecyyparis nootkatensis (D. Don) Spach, and incense cedar, Calocedrus decurrens (Torr.), essential oils, have been shown to have biological activity against a variety of mosquito and tick species. Although these components act as both repellents and insecticides, how they function in either capacity is unknown. Their use as mosquito control insecticides would be greatly increased if their mode of action is not the same as that of currently used commercial products. This study compared the lethal dosages for nootkatone, carvacrol, and thymoquinone by using colony strains of Anopheles gambiae Giles with known mutations at three different target sites. The altered target sites evaluated were the sodium channel para-locus mutation (L1014 F KDR) that confers permethrin resistance, the ACE-1 gene that confers organophosphate and carbamate resistance, and a gamma-aminobutyric acid receptor mutation of the Rdl locus conferring dieldrin resistance. Significant increases in lethal dose were not observed in any of the mosquito strains for any of the compounds tested compared with the doses required of chemicals with known modes of action at the mutated sites. Although the mode of action was not determined, this screening study indicates that none of these compounds interact at the target sites represented in the test mosquito strains. These compounds represent a different mode of action than existing chemicals currently used in mosquito control.
Extracellular papain is known to inhibit the anion transport function of the band 3 protein of the human red blood cell membrane. Previous work [Jennings, M. L., & Passow, H. (1979) Biochim. Biophys. Acta 554, 498-519] had suggested that this inhibition may result from the removal by papain of 5 000-10 000 daltons from the 35 000-dalton chymotryptic peptide of band 3. The present work shows, however, that papain also removes a small peptide from the C terminus of the 60 000-dalton chymotryptic peptide. The C-terminal amino acid sequence of this peptide is -Lys-Thr-Tyr. Whether or not this newly discovered action of papain is responsible for inhibiting anion transport is unknown. The effects of extracellular papain on the band 3 function have been characterized in detail. Papain inhibits Cl-Cl exchange in a high Cl medium by almost 90%. This inhibition appears to result from inhibition of the efflux step in the catalytic cycle for the transport, because papain does not inhibit the anion transport when it is assayed under influx-limited conditions. Moreover, since papain has no detectable effect on the dissociation constant for extracellular substrate (SO4) binding, the material removed by papain cannot be involved closely in the outward-facing substrate site. In contrast, removal of this material strongly (12-fold) reduces the affinity of the inhibitor 4,4'-dinitro-2,2'-stilbenedisulfonate for outward-facing sites. Therefore, stilbenedisulfonate binding involves portions of the band 3 molecule which are not intimately related to substrate binding.
Insecticides based on botanical sources have taken on increased attention due to differing modes of action from current insecticides in use and the view that they may be environmentally friendly. Thymoquinone, a component in the essential oil of incense cedar heartwood, has been shown to have insecticidal action against adult mosquitoes. This study evaluated relative toxicities of thymoquinone, selected derivatives of thymoquinone, hydroquinone, and arbutin to determine if any had similar or better activity. The intrinsic toxicities of hydroquinone and thymohydroquinone were not significantly different from thymoquinone, while libocedrol and arbutin were significantly less toxic.
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