Evaluation and optimization of the protocols for measuring cytochrome P450 activity in aphids

Cytochrome P450 enzymes play major roles in insect detoxification of plant toxins and insecticides. However, measuring P450 activity in aphids has variable success, and a reliable method is not available yet. In this study, we evaluated and optimized the method for measuring P450 activity in aphids using the 7-ethoxycoumarin as the substrate. First, we found that nicotinamide adenine dinucleotide phosphate and protective agents are not needed in the aphid P450 activity assay, and homogenizing the green peach aphid, Myzus persicae, in the microplate resulted in significantly higher P450 activities than those in Eppendorf tube. Homogenizing aphids in Eppendorf tube could grind tissues thoroughly and released uncharacterized compounds that could inhibit aphid and pig liver P450 activities, whereas aphids in the microplate likely could not be thoroughly ground and thus released fewer such inhibitors. Then, the microplate homogenization method was optimized to follows: one or two aphids were put into one well of the microplate and ground in phosphate buffer using pipette tips for 20 cycles, followed by addition of 7-ethoxycoumarin, and then incubated for 1 h at room temperature, after which glycine buffer-ethanol mixture was added to stop the reaction. This method is also suitable for the pea aphid, Acyrthosiphon pisum, and the bird cherry {square}oat aphid, Rhopalosiphum padi. These results emphasize the importance of considering inhibitory effect of endogenous compounds in insects on their P450 activity and provide one possible method to reduce this inhibitory effect.