Abstract
The activity of acetylcholinesterase of mites susceptible and resistant to organophosphates in the reaction with acylthiocholine esters and the properties of the non-specific esterases which hydrolyze α and β-naphthyl acetate was studied. The acetylcholinesterase activity of the susceptible strain was higher with propionylthiocholine as substrate than with acetylthiocholine, but that of the resistant strains was higher with acetylthiocholine than with propionylthiocholine. The activities of the enzymes of both strains with butyrylthiocholine as substrate were much lower than that with the other two substrates. An almost similar difference between the resistant and susceptible strain was observed in the Michaelis constants (Km) and maximal velocity (Vmax) of the reaction of the enzymes with the three acylthiocholine esters. Thus, the properties of the acetylcholinesterase from the resistant strains were characterized by lower Vmax and larger Km than those from the susceptible strain in the reaction with propionylthiocholine. Non-specific esterases responsible for the hydrolysis of α and β-naphthyl acetate had similar values for the bimolecular reaction constants (ki), inhibition constants (Ki) as well as similar esterase zymogram patterns as revealed by agar-gel electrophoresis.
