The inhibition of acetylcholinesterase by arsenite and fluoride

The effect of fluoride on the rate of reaction of acetylcholinesterase with arsenite, on the rate of dissociation of the enzyme-arsenite complex, and on the equilibrium between enzyme and arsenite was studied. Fluoride decreases the rate of the reaction between acetylcholinesterase and arsenite and changes the apparent equilibrium dissociation constant between the enzyme and arsenite, but even at concentrations as high as 0.2 M has no effect on the rate of dissociation of the enzyme-arsenite complex. The binding of fluoride and arsenite with the enzyme is highly anticooperative and may well be mutually exclusive. These results are consistent with a model in which the binding sites overlap and in which the same functional groups are involved.