Measurement of bimolecular rate constants k_iof the cholinesterase inactivation reaction by 55 insecticides and of the influence of various pyridiniumoximes on k_i

The cholinesterase (ChE) inhibition test is a biochemical method for screening insecticides. The possibilities for the detection of different cholinesterase inhibiting substances were investigated. The inactivation abilities against cholinesterases from 4 different biological origins were measured. General rules for detection and discrimination of insecticides were derived from the bimolecular rate constants k_iof 55 relevant organophosphorus compounds, carbamates and carbamate metabolites. The thionophosphates were converted into the more powerful inhibiting oxones by oxidation with N-bromosuccinimide. The inactivation values k_idiffer in some cases up to 6 orders of magnitude for different insecticides and 3 orders of magnitude for different enzymes. The inactivation of acetylcholinesterase (AChE) by organophosphorous compounds can be suppressed by reactivation with obidoxime. On the other hand, an acceleration of inactivation of butyrylcholinesterase (BChE) by carbofuran and certain other carbamates was observed under the influence of bispyridiniumoximes.