Noncompetitive inhibition of acetylcholinesterase by eserine

The inhibition of acetylcholinesterase by eserine was shown to be noncompetitive if the enzyme and inhibitor were allowed to preincubate for as short a time as 6 min, in the absence of substrate; when substrate and inhibitor are added simultaneously the inhibition is competitive. K i values of 3.1 × 10 −6 , 1.9 × 10 −7 and 1.0 × 10 −7 M were obtained at preincubation times of zero, 6.8 and 18.9 min respectively. The data are compatible with the concept that a reversible inhibitor-enzyme complex is initially formed and that carbamylation of the enzyme then proceeds slowly as the preincubation time is increased.