Dafforn A, Anderson M, Ash D, Campagna J, Daniel E, Horwood R, Kerr P, Rych G, Zappitelli F
Biochim Biophys Acta. 1977 Oct 13;484(2):375-85. doi: 10.1016/0005-2744(77)90093-6.
Phenylacetone, 4-phenyl-2-butanone, and 4-oxopentyltrimethylammonium chloride were tested as potential transition state analogs for eel acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7). Phenylacetone is a competitive inhibitor of the enzyme but not a transition state analog, since its binding constant is similar to that for the substrate phenyl acetate. 4-Phenyl-2-butanone binds 6-18 times more tightly than the inhibitors 4-phenyl-2-butanol and N-benzylacetamide and the substrate benzyl acetate and also blocks inactivation of the enzyme with methanesulfonyl fluoride. However, its binding is independent of pH in the range 5-7.5, whereas both V and V/Km for benzyl acetate hydrolysis decrease with decreasing pH in this range. These data indicate a specific but weak interaction between the ketone carbonyl and the enzyme, but probably do not justify considering this compound a transition state analog. 4-oxopentyltrimethylammonium iodide has previously been shown to bind about 125 times more strongly than the substrate acetylcholamine. It also binds about 375 times more strongly than the alcohol 4-hydroxypentyltrimethylammonium iodide. Furthermore, the ketone protects the enzyme from inactivation by methansulfony fluoride, while the corresponding quaternary ammonium alcohol accelerates this inactivation reaction. This additional information confirms that the ketone is a transition state analog.
对苯丙酮、4-苯基-2-丁酮和4-氧代戊基三甲基氯化铵作为鳗鱼乙酰胆碱酯酶（乙酰胆碱水解酶，EC 3.1.1.7）潜在的过渡态类似物进行了测试。苯丙酮是该酶的竞争性抑制剂，但不是过渡态类似物，因为其结合常数与底物乙酸苯酯的结合常数相似。4-苯基-2-丁酮的结合比抑制剂4-苯基-2-丁醇和N-苄基乙酰胺以及底物乙酸苄酯紧密6 - 18倍，并且还能阻止甲磺酰氟对该酶的失活作用。然而，其结合在pH值5 - 7.5范围内与pH无关，而在此范围内乙酸苄酯水解的V和V/Km均随pH降低而减小。这些数据表明酮羰基与酶之间存在特定但较弱的相互作用，但可能不足以认定该化合物为过渡态类似物。4-氧代戊基三甲基碘化铵先前已被证明其结合强度比底物乙酰胆碱强约125倍。它的结合强度也比醇类4-羟基戊基三甲基碘化铵强约375倍。此外，酮能保护该酶不被甲磺酰氟失活，而相应的季铵醇则加速这种失活反应。这些额外信息证实酮是一种过渡态类似物。
