Soomets U V, Palumaa P Ia, Iarv Ia L
Bioorg Khim. 1987 Feb;13(2):198-203.
Effect of temperature on the rate of the bond-breaking step of acetylcholinesterase modification with N,N-dimethylaziridinium ion was studied within 8 to 45 degrees C temperature interval. For this reaction measured by irreversible inhibition of the acetylcholinesterase-catalyzed hydrolysis of acetylthiocholine the activation parameters delta H not equal to = 94 kJ/mole and delta S not equal to (25 degrees C) = -9.4 J/mol X deg were obtained. Processing of these data together with our earlier results on spontaneous solvolysis of the aziridinium ion in various water-solvent mixtures showed that all these reactions form a common isokinetic series. That gave evidence of the SN1 mechanism of the alkylation reaction occurring at the acetylcholinesterase active centre. Kinetics of spontaneous decomposition of the covalent bond between the aziridinium reagent and protein molecule was studied. This reaction followed the first-order kinetics and lead to complete liberation of the label from the enzyme, thus suggesting that a single carboxylic or amide group in the active centre was modified by the aziridinium ion.
在8至45摄氏度的温度区间内，研究了温度对N，N - 二甲基氮丙啶离子修饰乙酰胆碱酯酶的断键步骤速率的影响。对于通过不可逆抑制乙酰硫代胆碱的乙酰胆碱酯酶催化水解来测量的该反应，获得了活化参数ΔH≠ = 94 kJ/mol和ΔS≠(25摄氏度)= -9.4 J/mol·deg。将这些数据与我们早期关于氮丙啶离子在各种水 - 溶剂混合物中的自发溶剂解的结果相结合进行处理，结果表明所有这些反应形成了一个共同的等动力学系列。这为在乙酰胆碱酯酶活性中心发生的烷基化反应的SN1机制提供了证据。研究了氮丙啶试剂与蛋白质分子之间共价键的自发分解动力学。该反应遵循一级动力学，并导致标记物从酶中完全释放，因此表明活性中心中的单个羧基或酰胺基团被氮丙啶离子修饰。
