Acetilcolinesterasa de Eisenia foetida como indicador de contaminación por plaguicidas organofosforados

Abstract

Organophosphates are among the most used and the most toxic pesticides that inhibit acetylcholinesterase. The enzyme aceticolinesterase (AChE) is widely used to detect organophosphate pollutants because they are inhibitors of its activity. A source of this enzyme is present in Eisenia foetida, being the AChEs of these earthworms susceptible to this effect. In this work, an enzymatic concentrate of acetylcholinesterase was prepared from E. foetida. The inhibitory effect of commercial organophosphorus pesticides as malathion, diazinon, methamidophos and dimethoate on its enzymatic activity was evaluated, as well as its selectivity when using organochlorine, carbamate and pyrethroid pesticides. Acetylcholinesterase activity was measured using indoxyl acetate as chromogenic substrate. Results showed that all organophosphorus pesticides tested, in concentrations between 1-10 mg/L, were able to decrease acetylcholinesterase activity in percentages of 36 ± 16 % on average. On the other hand, carbamates slightly inhibited the enzymatic activity in a 16 ± 7 %, and organochlorines and pyrethroids showed a little or no significant inhibitory effect of 1 ± 5 % for any tested concentrations. This is because the mode of action of each group of pesticides is different. For this reason, the activity of the enzyme is not significantly affected and it remains catalyzing the decomposition of indoxyl acetate even in the presence of pesticides with chemical groups different to organophosphates, which is indicative of acetylcholinesterase selectivity against this specific type of inhibitors.