TRANSPORT OF FREE FATTY ACIDS ACROSS MODEL MEMBRANES

游离脂肪酸（FFA）在细胞内和细胞外位点之间的运动 是哺乳动物能量循环的重要组成部分 在很多时候， 在细胞周期中，FFA必须穿过细胞膜。 了解分子 控制这种运动的机制是重要的，因为：1）FFA是 在数量上是最重要的生理能量来源; 2）FFA是 细胞行为的有效调节剂;和3）该循环提供了一种 一般来说，亲脂性分子的运动模式。 缺陷 周期中的任何这些步骤都可能导致营养失衡和/或 与FFA水平改变相关的各种病理学。 因为 FFA的生理重要性，以及对 两亲物运输，一般来说，FFA运输问题已收到 相当注意。 然而，没有达成共识：即使在大多数国家， 最近的文献，至于质膜是否是速率限制， FFA运输。 最近大量的研究表明，血浆 膜蛋白作为细胞内的转运蛋白， 长链FFA的摄取。 几乎所有的模型膜研究， 然而，已经证明FAA可以通过 纯脂囊泡的双层，提出了为什么运输的问题 通过质膜的脂质相不会使 蛋白质介导的转运。 事实上，由于这种观察， 通常认为FFA（事实上，大多数亲脂转运）是 而不是蛋白质介导的。 另一方面，我们自己的研究，虽然同意 FFA确实自发地通过脂质双层转移，表明对于 长链荧光FFA的触发速率比长链荧光FFA慢得多， 关闭率，相反的传统观点的两性渗透性，通过 脂质双层。 在初步研究中，我们发现， 触发器是膜脂组成的敏感功能，物理 状态和双层大小，这增加了脂质因子 可能会减慢触发器低于生理功能所需的速率， 至少是一些生物膜。 在研究中，我们将 研究荧光和天然FFA在细胞内的触发机制， 脂质囊泡，在红细胞和脂肪细胞血浆形成的囊泡中 膜，并在脂质囊泡与FFA运输重建 蛋白 我们的分析和解释方法将基于 严格使用特定的动力学模型。 各种实验和 理论技术将被开发，以建立这种有效性， 模型 在这个模式的基础上，我们会进行研究， 确定脂质成分和FFA结构和电荷状态如何影响 模型的内在速率常数。 虽然实验 用荧光FFA进行这些研究所需的技术代表了 我们以前的工作的一个简单的扩展，新的方法将 用于天然FFA的类似研究。

Movement of free fatty acids (FFA) between intra and extra-cellular sites is an essential part of the mammalian energy cycle. At many points in this cycle, FFA must cross a cellular membrane. Understanding the molecular mechanisms governing this movement is important since: 1) FFA are quantitatively the most important physiological energy source; 2) FFA are potent modulators of cellular behavior; and 3) this cycle provides a paradigm for the movement of lipophilic molecules, in general. Defects in any of these steps in the cycle may result in nutritional imbalances and/or various pathologies associated with altered levels of FFA. Because of the physiological importance of FFA, as well as the potential implication for amphiphile transport, in general, the FFA transport problem has received considerable attention. There is, however, no consensus: even in the most recent literature, as to whether the plasma membrane is rate limiting for FFA transport. A significant number of recent studies indicate that plasma membrane proteins play a key role as transport proteins in the cellular uptake of long chain FFA. Virtually all studies in model membranes, however, have demonstrated that FAA can spontaneously transfer through the bilayer of pure lipid vesicles, raising the question of why transport through the lipid phase of the plasma membrane does not short circuit the protein mediated transport. In fact, because of this observation, it has generally been argued that FFA (and, in fact, most lipohile transport) is not protein mediated. On the other hand, our own studies, while agreeing that FFA do spontaneously transfer through the lipid bilayer, show that for long chain fluorescence FFA the rate of flip-flop is much slower than the off rate, contrary to conventional views of amphipath permeability through lipid bilayers. In preliminary studies, we have found that the barrier to flip-flop is a sensitive function of membrane lipid composition, physical state, and bilayer size, which raises the possibility that lipid factors may slow flip-flop below the rate necessary for physiological function in at least some biological membranes. In the proposed research, we will investigate the flip-flop mechanism of both fluorescent and natural FFA in lipid vesicles, in vesicles formed from red cell and adipocyte plasma membranes, and in lipid vesicles reconstituted with a FFA transport protein. Our methods of analysis and interpretation will be based upon the rigorous use of a specific kinetic model. Various experimental and theoretical techniques will be developed to establish the validity of this model. With this model as basis, we will then carry out studies to determine how lipid composition and FFA structure and charge state affect the intrinsic rate constants of the model. While the experimental techniques needed to carry out these studies with fluorescent FFA represent a straightforward extension of our previous work, new methods will be developed for similar studies of natural FFA.