Mechanism of the Inhibition of Rat Brain Cholinesterase by Diisopropylfluorophosphate, Tetraethylpyrophosphate, and Eserine.

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Abstract
The mechanism of inhibition of rat brain cholinesterase by the 3 most potent anti-cholinesterases, diisopropylfluorophosphate, tetraethylpyrophosphate, and eserine was studied by a method which involves variation in enzyme concentration as well as inhibitor concentration. It was shown that the kinetics of eserine-inhibition may be analyzed by classical methods which ignore enzyme concentration but the cases of the other two inhibitors may not be so treated. Cholinesterase inhibition by the fluoro- and pyrophosphates was shown to be irreversible and to depend upon enzyme concentration and time of incubation of the enzyme with the inhibitor before the addition of substrate. The upper limit of cholinesterase concentration in rat brain was estimated to be 1 × 10-6 molar if structural restrictions are not assumed.