Differential effects of denaturing agents on acetylcholinesterase: insensitivity of the reaction of methanesulfonyl fluoride compared to diisopropylphosphorofluoridate and p-nitrophenyl acetate.

The effects of various agents that could be expected to perturb enzyme structure in a non-specific and reversible manner (alcohols, dimethylsulfoxide, dimethylformamide, dinitrobenzene, urea and guanidine - HCl) have been determined on reaction of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) with a substrate, p-nitrophenyl acetate, and two irreversible inhibitors, diisopropylphosphorofluoridate and methanesulfonyl fluoride. In all three of these reactions an acyl group (acetyl, phosphoryl or sulfonyl respectively) bonds covalently with the active center of the enzyme. As expected, the reactions of p-nitrophenyl acetate and diisopropylphosphorofluoridate were severely retarded by most of these agents. By contrast, reaction of methanesulfonyl fluoride was usually depressed to a far smaller degree, and in two cases was faster. These findings are of interest in connection with: (1) differing requirements for the integrity of tha active center in catalysis with various substrate analogs, and (2) the mechanism by which cationic substrate analogs accelerate reaction of the enzyme with methanesulfonyl fluoride.