Acetylcholinesterase: theory of noncompetitive inhibition.

The theory of noncompetitive inhibition of acetylcholinesterase based on the binding of inhibitor to the acetylenzyme and the free enzyme was proven correct by demonstrating that tripropylammonium ion increases the steady-state concentration of acetylenzyme, as predicted by the theory. By contrast, the traditional theory that the inhibitor binds to the enzyme-substrate complex and the free enzyme predicts that the amount of acetylenzyme will be drastically reduced when the inhibition is high. A third theory involving all three types of binding remains possible.