Acetylcholinesterase: inhibition by tetranitromethane and arsenite. Binding of arsenite by tyrosine residues.

Tetranitromethane inhibits acetylcholinesterase with respect to the hydrolysis of both acetylthiocholine and indophenyl acetate. The loss of activity with indophenyl acetate, a poor substrate, is preceded by an increase in enzyme activity. Only 12 of the 21 tyrosine residues/monomer of enzyme are susceptible to nitration. Loss of activity with respect to indophenyl acetate occurs well after no further nitration of tyrosines occurs and must be due to the modification of other residues. Incubation of the enzyme with arsenite before nitration results in the nitration of only 10 tyrosines. This experiment reveals that the structural basis for the binding of arsenite is the formation of a diester with two tyrosine residues.