Effect of ions on the activity of brain acetylcholinesterase from tropical ifsh

Objective:To investigate the effect of ions on brain acetylcholinesterase(AChE;EC 3.1.1.7)activities from economic important fish[pirarucu,Arapaima gigas;tambaqui,Colossoma macropomum;cobia,Rachycentron canadum(R.canadum)and Nile tilapia,Oreochromis niloticus(O.niloticus)]comparing with a commercial enzyme from electric eel[Electrophorus electricus(E.electricus)].Methods:Thein vitro exposure was performed at concentrations ranging from 0.001 to 10 mmol/L(except for ethylene diamine tetraacetic acid;up to 150 mmol/L).Inhibition kinetics onR.canadum andO.niloticus were also observed through four methods(Michaelis-Menten,Lineweaver-Burk,Dixon and Cornish-Bowden plots)in order to investigate the type of inhibition produced by some ions.Results:Hg^(2+),As^(3+),Cu^(2+),Zn^(2+),Cd^(2+)caused inhibition in all the species under study.Ca^(2+),Mg^(2+)and Mn^(2+)induced slight activation inR.canadum enzyme while Pb^(2+),Ba^(2+),Fe^(2+),Li+inhibited the AChE from some of the analyzed species.The lowest IC50 and Ki values were estimated forE.electricus AChE in presence of Hg^(2+),Pb^(2+),Zn^(2+).Under our experimental conditions,the results forR.canadum andO.niloticus,As^(3+),Cu^(2+),Cd^(2+),Pb^(2+)and Zn^(2+)showed a non-competitive/mixed-type inhibition,while Hg^(2+)inhibited the enzyme in a mixed/competitive-like manner.Conclusions:E.electricus AChE activity was affected by ten of fifteen ions under study showing that this enzyme could undergo interference by these ions when used as pesticide biosensor in environmental analysis.This hindrance would be less relevant for the crude extracts.