Characterization of cholinesterase activity in tissues of the grass shrimp ( Palaemonetes pugio)

Abstract

Inhibition of cholinesterases in estuarine organisms is a useful indicator of organophosphorus insecticide exposure. Recent research has indicated that more than one cholinesterase may be present in tissues of estuarine organisms and that these cholinesterases vary in their sensitivity to organophosphorus insecticides. Baseline cholinesterase activity for adult grass shrimp ( Palaemonetes pugio) was determined with four substrates (acetylthiocholine iodide, acetyl-β-methylthiocholine iodide, propionylthiocholine iodide, S-butyrylthiocholine iodide) and three cholinesterase inhibitors (eserine sulfate, tetraisopropyl pyrophosphoramide, 1,5-bis(4-allyldimethyl-ammoniumphenyl) pentan-3-one dibromide). Cholinesterase activity was the highest with acetylthiocholine iodide at 57.42 nmol/mg P/min and the lowest with acetyl-β-methylthiocholine iodide at 6.17 nmol/mg P/min. The four substrates tested were not inhibited by tetraisopropyl pyrophosphoramide. Eserine sulfate significantly inhibited cholinesterase activity against all substrates except S-butyrylthiocholine iodide. The results of substrate specificity and cholinesterase inhibition in grass shrimp indicate that acetylthiocholine iodide is the most appropriate substrate for assessing cholinesterase inhibition in grass shrimp.