Organophosphates irreversibly and non-competitively inhibit acetylcholinesterase, causing poisoning by phosphorylating the serine hydroxyl residue on AChE, which inactivates AChE. AChE is critical for nerve function, so the inhibition of this enzyme, which causes acetylcholine accumulation, results in muscle overstimulation. This causes disturbances across the cholinergic synapses and can only be reactivated very slowly, if at all. Paraoxonase (PON1) is a key enzyme involved in OP toxicity and has been found to be critical in determining an organism's sensitivity to OP exposure.