Characterization of cholinesterase from guppy (Poecilia reticulata) muscle and its in vitro inhibition by environmental contaminants

With a view to using the cholinesterase (ChE) activity from guppy (Poecilia reticulata) muscle as a biomarker, the objectives of this work were: (i) to characterize the soluble cholinesterases present in muscle homogenate using different substrates and specific inhibitors, (ii) to determine the normal range of activity in non-exposed individuals and (iii) to investigate the in vitro effects of two common environmental contaminants, copper sulphate and dodecylbenzene sulphonic acid sodium salt (DBS) on ChE activity. The rate of substrate hydrolysis of P. reticulata ChE decreased in the order acetylthiocholine, propionylthiocholine and butyrylthiocholine. Inhibition by excess of substrate was observed at concentrations higher than 1.28 mM. Furthermore, eserine sulphate and 1,5-bis(4-allyldimethylammoniumphenyl) -pentan-3-one (BW284C51) significantly inhibited the enzyme activity at low concentrations (mM range) and N,N'-diisopropylphosphorodiamic acid (iso-OMPA) had no significant effect up to 8 mM. These findings suggest that the enzyme measured in this study is acetylcholinesterase. The activity determined in non-exposed fish was 145.1+/-44.7 SD U mg(-1) protein. The common environmental contaminants copper and DBS significantly inhibited P. reticulata ChE at concentrations that can be ecologically relevant.