Sepp A, Järv J
Laboratory of Bioorganic Chemistry, Tartu University, Estonia, U.S.S.R.
Biochim Biophys Acta. 1991 Apr 29;1077(3):407-12. doi: 10.1016/0167-4838(91)90558-h.
Affinity labelling of acetylcholinesterase (EC 3.1.1.7, acetylcholine acetylhydrolase) anionic centre with N,N-dimethyl-2-phenylaziridinium ion accelerates the hydrolysis of non-ionic acetic esters by increasing the rate of the enzyme acylation step at least 500-times while the rate of the deacylation step remains unchanged. Simultaneously, at least a 10-fold decrease of the substrate binding affinity takes place. The acceleration phenomenon can be explained by the "induced fit" mechanism as the binding of the cationic label to the enzyme anionic site brings the esteratic centre into conformation which provides extra stabilization for the transition state of the enzyme acylation reaction, probably by a more close structural fit between the substrate molecule and the enzyme active centre.
用N，N-二甲基-2-苯基氮丙啶离子对乙酰胆碱酯酶（EC 3.1.1.7，乙酰胆碱乙酰水解酶）阴离子中心进行亲和标记，通过将酶酰化步骤的速率提高至少500倍，加速了非离子型乙酸酯的水解，而去酰化步骤的速率保持不变。同时，底物结合亲和力至少降低了10倍。这种加速现象可以用“诱导契合”机制来解释，因为阳离子标记物与酶阴离子位点的结合使酯解中心形成一种构象，这种构象可能通过底物分子与酶活性中心之间更紧密的结构契合，为酶酰化反应的过渡态提供额外的稳定性。
