Cholesterol esterase catalyzed hydrolysis of mixed micellar thiophosphatidylcholines: a possible charge-relay mechanism.
Cholesterol esterase catalyzed hydrolysis of mixed micellar thiophosphatidylcholines: a possible charge-relay mechanism.
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胆固醇酯酶催化混合胶束硫代磷脂酰胆碱的水解：可能的电荷中继机制。
DOI：
10.1021/bi00238a012
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发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
Quinn,DM
中科院分区：
文献类型：
--
作者：
Sutton,LD;Froelich,S;Hendrickson,HS;Quinn,DM
8 月 20 日，¡ 990；修订稿于 1991 年 3 月 21 日收到摘要：胆固醇酯酶催化水解两种硫代磷脂，rae-l-(己酰硫基)-2-己酰基-3-甘油磷酰胆碱 (6TPC) 和 rae·1-(癸酰硫基)-2-癸酰基-3-甘油磷酰胆碱 (10TPC) 的机理，具有被表征。 Triton X-100 混合胶束中包含的 10TPC 的水解严格发生在胶束界面，因为反应速率与胶束浓度无关，但双曲线取决于胶束中底物的摩尔分数。后一种观察允许计算界面动力学参数 V* mix 和 K* m。 10TPC 和丁酸对硝基苯酯的水解同样受到过渡态类似物抑制剂苯基正丁基硼酸的抑制，因此生理和非生理底物在相同的活性位点进行处理。酰基相似底物 10TPC 和对硝基苯基癸酸酯的 &* 值的相似性表明，磷脂酶 A、胆固醇酯酶的活性部分地受到癸酰基酶中间体的转换的速率限制。溶剂同位素对F ax 和 （仅监测酰化）的影响约为2-3，并且与通过一般酸碱质子转移稳定的过渡态一致。 K“m 的质子库存表明，同时的质子转移稳定了酰化过渡态，这需要多功能酸碱机器（可能是一个
August 20,¡ 990; Revised Manuscript Received March 21, 1991 abstract: Mechanistic features of cholesterol esterase catalyzed hydrolysis of two thiophospholipids, rae-l-(hexanoylthio)-2-hexanoyl-3-glycerophosphorylcholine (6TPC) and rae· 1-(decanoylthio)-2-decano-yl-3-glycerophosphorylcholine (10TPC), have been characterized. The hydrolysis of 10TPC that is contained in mixed micelles with Triton X-100 occurs strictly at the micellar interface, since the reaction rate is independent of the micelle concentration but depends hyperbolically on the mole fraction of the substrate in the micelles. This latter observation allows one to calculate the interfacial kinetic parameters V* mix andK* m. The hydrolyses of 10TPC and p-nitrophenyl butyrate are similarly inhibited by the transition state analogue inhibitor phenyl-n-butylborinic acid, and therefore, physiological and nonphysiological substrates are processed atthe same active site. The similarity of &* at values for the acyl-similar substrates 10TPC and p-nitrophenyl decanoate indicates that the phospholipase A, activity of cholesterol esterase is partially rate limited by turnover of a decanoyl-enzyme intermediate. Solvent isotope effects on F^ ax and (which monitors acylation only) are~ 2-3 and are consistent with transition states that are stabilized by general acid-base proton transfers. Proton inventories of K “m indicate that simultaneous proton transfers stabilize the acylation transition state, which requires a multifunctional acid-base machinery (perhaps a