Most insect possess two AChEs (i.e., AChE1 and AChE2 encoded by ace1 and ace2 gene, respectively). Due to its higher transcription level and responsibility for insecticide resistance, it is believed that AChE1 is likely the main catalytic AChE, between two AChEs of the insects having both AChE1 and AChE2 studied to date. However, Cyclorrhaphan flies have only AChE2, suggesting the evolutionary scenarios for the takeover of ace2 and the loss of ace1 during Diptera evolution (Huchard et al., 2006). Therefore, it is essential to investigate the evolutionary distribution of AChE1 and AChE2 in Insecta. In this study, among 100 insect species examined, we found 33 species expressing AChE2 as the catalytic major enzyme by Western blotting using AChE1- and AChE2 specific antibodies. These findings are contrary to the common expectation that AChE1 is dominant synaptic enzyme in all insect species with the exception of Cyclorrhapha. In this study, we compared the characteristics of both AChE1 and AChE2 from the German cockroach and the honey bee, in which AChE1 and AChE2 were expressed as major catalytic enzyme, respectively. In addition, we presented a unique case of a damselfly, which expresses both AChEs exhibiting almost identical enzymatic activities, along with the fruit fly, where AChE1 is not present but multiple forms of AChE2 appear to replace the function of AChE1. The current study will provide valuable insights into the evolution of AChE.

• Young Ho Kim(Research Institute for Agriculture and Life Sciences, Seoul National University)
• Si Hyeock Lee(Research Institute for Agriculture and Life Sciences, Seoul National University, Department of Agricultural Biotechnology, Seoul National University)