Characterization of cholinesterase from guppy (Poecilia reticulata) muscleand 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) t o characterize the soluble cholinesterases present in muscle homogenate usi ng different substrates and specific inhibitors, (ii) to determine the norm al range of activity in non-exposed individuals and (iii) to investigate th e in vitro effects of two common environmental contaminants, copper sulphat e and dodecylbenzene sulphonic acid sodium salt (DBS) on ChE activity. The rate of substrate hydrolysis of P. reticulata ChE decreased in the order ac etylthiocholine, propionylthiocholine and butyrylthiocholine. Inhibition by excess of substrate was observed at concentrations higher than 1.28 mM. Fu rthermore, eserine sulphate and 1,5-bis(4-allyldimethylammoniumphenyl) -pen tan-3-one (BW284C51) significantly inhibited the enzyme activity at low con centrations (mM range) and N,N'-diisopropylphosphorodiamic acid (iso-OMPA) had no significant effect up to 8 mM. These findings suggest that the enzym e measured in this study is acetylcholinesterase. The activity determined i n non-exposed fish was 145.1+/-44.7 SD U mg(-1) protein. The common environ mental contaminants copper and DBS significantly inhibited P. reticulata Ch E at concentrations that can be ecologically relevant.