Section: Biological and Biochemical Foundations of Living Systems

9) Diisopropylfluorophosphate (DFP) binds to the active site of acetylcholinesterase (ACE) in the synapses of neurons. When DFP binds to ACE, the ACE enzyme is rendered permanently inactive. This makes DFP a potent toxin, with lethal amounts at less than 100 mg. The interaction between DFP and ACE can best be characterized as:

1. Competitive inhibition
2. Noncompetitive inhibition
3. Irreversible inhibition
4. Partially competitive inhibition

A: Competitive inhibitors bind to the active site but bind reversibly: they do not permanently disable the enzyme. By adding very high levels of the normal substrate, the effects of competitive inhibitors can be overcome. B: Noncompetitive inhibitors bind to a site other than the active site. D: Partially competitive inhibitors bind to a site other than the active site and allow the enzyme to still have some catalytic activity (typically reduced, but possible to be higher).