Comparative distribution and kinetic properties of acetylcholinesterase from Apis mellifera and Apis cerana
Ying Zhang, Xiwu Gao and Jian Huang
We determined the distribution of acetylcholinesterase (AChE) activities in extracts from the head, thorax and abdomen of Apis cerana cerana and Apis mellifera ligustica. There was no statistical difference in the AChE activity from the head or abdomen between the two honey bee species. However, AChE activity in the thorax was significantly greater (P < 0.01) in A. cerana than in A. mellifera. The substrate specificity and the sensitivity to inhibitors of AChEs from the head of two species were studied using acetylthiocholine iodide (ATCh), acetyl- (ß-methyl) thiocholine (MeTCh), s-propionylthiocholine (PrTCh) and s-butyrylthiocholine iodide (BuTCh) as substrates and eserine, propoxur, thiodicarb and methomyl as inhibitors, respectively. There was no statistical difference in AChE affinities toward the four substrates between A. mellifera and A. cerana based on comparison of the Michaelis constant (Km) values. However, the hydrolyzing efficiency of AChE from A. mellifera for four substrates was significantly higher than that from A. cerana. Among the tested inhibitors, eserine was the most potent inhibitor to AChEs of both bees; the bimolecular reaction constant (ki) was 400.3 for A. mellifera and 340.3 for A. cerana. Responses of AChE to carbamate insecticides differed for the bees. For A. mellifera, kis were: propoxur = 5.7, thiodicarb = 5.2 and methomyl = 4.9. For A. cerana, kis were: methomyl = 10.4, propoxur = 4.6 and thiodicarb = 4.2. AChE from A. mellifera thus was more sensitive to inhibitors than AChE from A. cerana.