Localization and properties of cholinesterases in the common prawn (Palaemon serratus): A kinetic-histochemical study

Due to the diversity in biochemical properties and tissue distribution of cholinesterase (ChE) enzymes, a characterization should be performed before they are used as biomarkers for monitoring pesticide contamination. In this study we investigate the distribution of ChEs and their kinetic properties in diverse tissues of the common prawn Palaemon serratus. The results concerning the histochemical localization of ChEs suggest that the highest amount of ChE activity occurs in prawn eyes, followed by the brain, gills, and digestive tract. Negligible staining was observed in the muscle. We describe the kinetic properties of ChEs in eyes, gills, and hepatopancreas, investigating their substrate preferences with different thiocholine esters and their sensitivity to inhibition with selective inhibitors. The results suggest that the studied enzymes are ChEs and not nonspecific esterases, due to their apparent affinity for choline esters, with a distinct preference for the substrate acetylthiocholine, and their high sensitivity to inhibition by eserine sulfate. P. serratus eyes can be considered the best tissue for recovery of ChE enzyme: this tissue is easy to isolate, it expresses high levels of ChE, and the enzyme shows properties of a vertebrate AChE.