ENZYMATIC REACTION MECHANISM OF ACETYL CHOLINE ESTERASE---THEORETICAL RESEARCH FOR DEVELOPMENT OF ANTIDEMENTIA AGENT

乙酰胆碱酯酶是一种丝氨酸蛋白酶，在胆碱能突触上特异性地作用于神经递质乙酰胆碱，水解为胆碱和乙酸。该抑制剂能保持乙酰胆碱，并能强烈地刺激胆碱能作用。近年来，这种抑制剂被认为是一种新型药物，一种抗痴呆剂，它可以改善大脑皮层中乙酰胆碱缺乏引起的阿尔茨海默病症状。本论文以开发新的抗痴呆药物为目标，运用量子化学和分子动力学方法，从原子水平上研究乙酰胆碱酯酶的酶促反应机理。结果表明：（1）Glu 199是唯一一个能作为“阴离子位点”的残基，它能在水解过程中将乙酰胆碱的季铵阳离子固定在合适的位置上。这种情况对于乙酰胆碱酯酶的极高比率是合理的。(2)由“催化三联体”构成的活性中心反应模型的理论计算（Ser 200-His 40-Glu 327）、乙酰胆碱、Glu 199作为阴离子位点、两个甘氨酸作为“含氧阴离子空穴”，揭示了Blow在1969年提出的质子传递机制是有效的，其中在活性中心产生Ser-O阴离子的速率决定步骤分为两个步骤，活化能降低10千卡/摩尔。这是一个重要的支持质子中继机制，这一直是一个讨论点的丝氨酸蛋白酶的酶促作用。(3)总结了我们的研究工作，并提出了抑制剂药物设计的指导原则。

Acetylcholine esterase is one of serine-protease, whic singularly acts on acetylcholine, a neuro-chemical transmitter, to hydrolyze into choline and acetic acid at cholinargetic synapses. The inhibitor can remain acetylcholine and stimulate cholinargetic action strong. Recently the inhibitor is noted to be a novel medicine, an anti-dementia agent, which improves Alzheimer symptoms induced from deficiency of acetylcholine in cerebral cortex. Aiming at development of new anti-dementia, we investigate the enzymatic reaction mechanism of acetylcholine esterase at the atomic level by means of quantum chemistry and molecular dynamics. The results obtained are as follows : (1) Glu 199 is the only one residue that can act as the "anionic site", which can hold a quaternary ammonium cation of acetylcholine at the appropriate position during the hydrolysis. This situation is reasonable for such an extremely high rate of acetylcholine esterase. (2) Theoretical calculations on a reaction model for the active site constructed from the "catalytic triad" (Ser 200-His 40-Glu 327), acetylcholine, Glu 199 as the anionic site, and two glycines as the "oxyanion hole", reveal that the protonrelay mechanism suggested by Blow in 1969 is valid effectively, where the rate-determining step generating the Ser-O anion at the active center is divided into two steps and the activation energy is reduced by 10 kcal/mol lower. This is a significant support for the proton-relay mechanism which has been a point of discussion on the serine-protease enzymatic action. (3) We summarized our research and proposed a guiding principle for the drug-design of the inhibitor.