Cytochrome P450 in Plant-Insect Interactions: Inductions and Deductions
Although it is now known that cytochrome P450 monooxygenases have a number of physiological functions in insects, including hormone and pheromone metabolism, they were first recognized as a general purpose system for metabolizing xenobiotics, particularly synthetic organic insecticides. In the early sixties, a series of experiments revealed that high levels of oxidase activity were associated with resistance to insecticides and that administration of known oxidase inhibitors, such as sesamex or piperonyl butoxide, could reverse that resistance. Subsequently, detoxification via microsomal monooxgenases of such insecticides as propoxur, carbaryl, and aldrin was demonstrated. The fact that insect strains selected for resistance to one class of insecticide often displayed resistance to other groups of insecticides suggested that the microsomal monooxygenase system was broadly substrate-specific (Hodgson, 1985). The microsomal cytochrome P450- dependent mono-oxygenase system was subsequently found to consist of a suite of membrane-bound enzymes that effect a variety of oxidation reactions; the heme protein cytochrome P450 is the terminal oxidase in the series. In general, since oxidation increases the hydrophilicity of a substrate, P450 monooxygenases can act as detoxification enzymes; with reduced lipophilicity, a substrate is at the same time rendered more likely to be excreted and, in the process, less able to cross lipid rich membranes to interfere with biological processes.
KeywordsPyrimidine Epoxidation Coumarin Phenobarbital Flavone
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