1. Plant phenolics are detoxified by prophenoloxidase in the insect gut.
- Author
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Wu K, Zhang J, Zhang Q, Zhu S, Shao Q, Clark KD, Liu Y, and Ling E
- Subjects
- Animals, Biotransformation, Bombyx genetics, Bombyx metabolism, Catechol Oxidase deficiency, Drosophila melanogaster genetics, Enzyme Precursors deficiency, Gene Deletion, Gene Expression, Hemolymph metabolism, Indoles metabolism, Insect Proteins deficiency, Intestinal Mucosa metabolism, Lepidoptera genetics, Levodopa metabolism, Plant Extracts administration & dosage, Plant Extracts metabolism, Plants chemistry, Bombyx enzymology, Catechol Oxidase genetics, Drosophila melanogaster enzymology, Enzyme Precursors genetics, Insect Proteins genetics, Lepidoptera enzymology, Metabolic Detoxication, Phase I genetics, Phenols metabolism
- Abstract
Plant phenolics are a group of important secondary metabolites that are toxic to many animals and insects if ingested at high concentrations. Because most insects consume plant phenolics daily, they have likely evolved the capacity to detoxify these compounds. Here, we used Drosophila melanogaster, Bombyx mori and Helicoverpa armigera as models to study the metabolism of plant phenolics by prophenoloxidases. We found that insect foreguts release prophenoloxidases into the lumen, and that the survival of prophenoloxidase-deletion mutants was impaired when fed several plant phenolics and tea extracts. Using l-DOPA as a model substrate, biochemical assays in large Lepidopteran insects demonstrated that low levels of l-DOPA are rapidly metabolized into intermediates by phenoloxidases. Feeding with excess l-DOPA showed that the metabolic intermediate 5,6-dihydroxyindole reached the hindgut either by passing directly through the midgut, or by transport through the hemolymph. In the hindgut, 5,6-dihydroxyindole was further oxidized by prophenoloxidases. Intermediates exerted no toxicity in the hemocoel or midgut. These results show that plant phenolics are not toxic to insects unless prophenoloxidase genes are lost or the levels of phenolics exceed the catalytic activity of the gut prophenoloxidases.
- Published
- 2015
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