Concentration-dependent self-quenching of the fluorescent phospholipid N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (N-NBD-PE) was used to measure the rate of N-NBD-PE transfer between phosphatidylcholine-bile salt mixed micelles. In a previous study using the same technique, the rate of N-NBD-PE transfer between phosphatidylcholine-taurocholate mixed micelles was found to be several orders of magnitude faster than its transfer between phosphatidylcholine vesicles as a result of an increased rate of transfer through the water at low micelle concentrations and an increased rate of transfer during transient micelle collisions at higher micelle concentrations [Nichols, J. W. (1988) Biochemistry 27, 3925-3931]. In this study we have determined the influence of bile salt structure, incorporation of cholesterol, and temperature on the rate and mechanism of phospholipid transfer between mixed micelles. We found that both transfer pathways were a common property of mixed micelles prepared from a series of different bile salts and that the rates of transfer by both pathways increased as a function of the degree of bile salt hydrophobicity. Cholesterol incorporation into phosphatidylcholine-taurocholate mixed micelles displaced taurocholate from the micelles and resulted in an increased rate of transfer through the water and a decreased rate of transfer during micelle collisions. The temperature dependence of the transfer rates was used to calculate the activation free energy, enthalpy, and entropy for both mechanisms. The activation enthalpy was the major barrier to transfer by both mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

译文

荧光磷脂N-(7-硝基-2,1,3-苯并恶二唑-4-基) 磷脂酰乙醇胺 (N-NBD-PE) 的浓度依赖性自猝灭用于测量磷脂酰胆碱-胆盐混合胶束之间的N-NBD-PE转移速率。在先前使用相同技术的研究中,发现磷脂酰胆碱-牛磺胆酸盐混合胶束之间的N-NBD-PE转移速率比其磷脂酰胆碱囊泡之间的转移速率快几个数量级,这是由于在低胶束浓度下通过水的转移速率增加以及在较高胶束浓度下瞬时胶束碰撞过程中的转移速率增加 [·尼科尔斯,J. W. (1988) 生物化学27,3925-3931]。在这项研究中,我们确定了胆汁盐结构的影响,和温度对混合胶束之间磷脂转移速率和机制的影响。我们发现这两种转移途径是由一系列不同胆汁盐制备的混合胶束的共同性质,并且这两种途径的转移速率随胆盐疏水性程度的变化而增加。胆固醇掺入磷脂酰胆碱-牛磺胆酸盐混合胶束从胶束中取代牛磺胆酸盐,导致通过水的转移速率增加,胶束碰撞过程中转移速率降低。转移速率的温度依赖性用于计算活化自由能,两种机制的焓和熵。激活焓是两种机制转移的主要障碍。(摘要截断为250字)

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