Kinetic and physicochemical properties of brain acetylcholinesterase from the peacock bass (Cichla ocellaris) and in vitro effect of pesticides and metal ions

Brain acetylcholinesterase (AChE; EC 3.1.1.7) from peacock bass (Cichla ocellaris) was characterized and the effect of organophosphorus and carbamate pesticides as well as ions and heavy metals was evaluated. The kinetic parameters Km and Vmax were determined as 0.769 mM and 0.189 U/mg of protein respectively. Optimal pH and temperature were found to be 8.0 and 45 °C. The enzyme retained approximately half of the activity after incubation at 50 °C for 30 min. Total cholinesterase activity on brain of this species can be ascribed to AChE according to selective inhibitors analysis (neostigmine, eserine and BW284c5 reduced its activity whereas no effect was noticed for Iso-OMPA). Seven pesticides (five organophosphates: dichlorvos, diazinon, chlorpyrifos, temephos, tetraethyl pyrophosphate – TEPP and two carbamates: carbaryl and carbofuran) showed inhibitory effects on C. ocellaris AChE. However, the strongest effect was observed with carbofuran (IC50 = 0.21 μM and Ki = 2.57 × 10−3 μM). The following ions (1 mM) showed to inhibit its activity (decrescent order): Hg2+ > As3+ > Cu2+ > Zn2+. EDTA2− did not affect enzyme activity. The present study provides assay conditions and data to suggest this enzyme as in vitro biomarker of organophosphorus and carbamate pesticides in routine environmental screening programs.

► Brain ChE from Cichla ocellaris was physicochemical and kinetically characterized.
► Selective inhibitors showed AChE as the main ChE in C. ocellaris brain.
► The enzyme was in vitro exposed to seven pesticides and fifteen ions.
► Inhibition parameters were determined in relation to the pesticides and ions.
► C. ocellaris brain AChE was strongly inhibited by carbofuran and the mercury ion.