Binding sites of cholinesterases. Alkylation by an aziridinium derivative

1. Alkylation of acetylcholinesterase and butyrylcholinesterase by 2-chloro-N-(chloroethyl)-N-methyl-2-phenylethylamine was observed. This alkylating agent was more potent than related compounds previously described, and less stable (half-life 8·5min. at 23°). 2. Alkylation had effects on hydrolysis of substrates varying from activation for indophenyl acetate to inhibition for acetylcholine, and intermediate effects with five other substrates. The effects were on V_max. and not K_m. 3. Alkylation caused a variety of changes in sensitivity to inhibition by five carbamates, five organophosphates and four other inhibitors, varying from total protection against tetraethylammonium to mildly enhanced sensitivity to urea. 4. The findings suggested the existence of three binding sites, one of which was anionic and another hydrophobic, in addition to the esteratic site.