Acetilcolinesterase, butirilcolinesterase, carboxilesterase e a resistência de peixes neotropicais aos pesticidas organofosforados

Abstract

Every human group who organizes to work together uses rivers, lakes or ponds as places in which undesirable substances are deposited for decomposition. Contamination of the aquatic environment with herbicides and pesticides derived from agricultural practices has become a problem of global importance since a long ago. We need detailed information on the biochemistry of the poisoning of native fish to assess the effects of pesticides on the biochemical processes that maintain fishes life cycle in waters of Brazil. Organophosphates, which are widely used pesticides, can interact with the B-esterases butyrylcholinesterase (EC 3.1.1.8) and carboxylesterase (EC 3.1.1.1) in plasma and liver. Butyrylcholinesterase (BChE) and carboxylesterase (CarbE) in relatively high concentrations act as stoichiometric scavengers by linking the phosphorus atom of the P=O group with the serine s hydroxyl they have in their active site. Our results show that the CarbE of curimbata plasma (IC50 74 ηm) is more sensitive to the organophosphate metilparaoxon than CarbE of pacu plasma (IC50 691 ηm). We isolated CarbE from curimbata and pacu s plasma. Piavussu does not have an expressive activity of CarbE in plasma, so we did not isolate it. The type and distribution of esterases in tissues are peculiar to a species. Curimbata has high CarbE activity in the liver (237.8 U.g-1) and blood (29.85 U.mL-1), pacu is equipped with high activities of BChE (134.0 U.g-1) and CarbE (149.6 U.g-1) in the liver and piavussu relies only on BChE of blood (17.87 U.g-1). This enzymatic arsenal was sufficient to protect AChE from brain, muscle and heart of the three species and protect them against mild intoxication by methylparathion (0.2 mg / L). The biochemical kinetic approach that allows understanding of the inhibition of the esterases in tissues of different fish species is a good tool capable of anticipating the harmful consequences of these drugs.