TRANSPORT OF FREE FATTY ACIDS ACROSS MODEL MEMBRANES

游离脂肪酸(FFA)在胞内和胞外的运动 是哺乳动物能量循环中必不可少的一部分。在这个过程中的许多点上 循环，FFA必须穿过细胞膜。理解分子 管理这一运动的机制很重要，因为：1)FFA是 数量上是最重要的生理能量来源；2)游离脂肪酸是 细胞行为的有效调节器；以及3)这个循环提供了一个 一般情况下，亲脂分子运动的范例。中的缺陷 周期中的任何一个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。因为 FFA的生理意义，以及对 水陆两栖运输，总体来说，FFA的运输问题已经收到 相当多的关注。然而，没有达成共识：即使是在最 最近的文献，关于质膜是否对 FFA运输。最近的大量研究表明，血浆 膜蛋白在细胞内起着运输蛋白的关键作用。 摄取长链游离脂肪酸。几乎所有关于模型膜的研究， 然而，已经证明联邦航空局可以自发地通过 纯脂泡的双层，提出了为什么运输的问题 通过脂相的质膜不会短路 蛋白质介导的运输。事实上，由于这种观察，它已经 普遍认为，FFA(事实上，大多数亲脂运输)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，这表明对于 长链荧光FFA触发器的速度比触发器慢得多 Off率，与传统的两足动物渗透率相反 脂质双分子层。在初步研究中，我们发现， 触发器是一种对膜脂成分敏感的物理函数 状态和双层大小，这增加了脂质因素 可能会将触发器减慢到生理功能所需的速率以下 至少是一些生物膜。在拟议的研究中，我们将 研究了荧光和天然FFA的触发机制 红细胞和脂肪细胞浆形成的囊泡中的脂泡 膜，以及在用FFA转运重建的脂囊中 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 将开发理论技术来确定这一点的有效性。 模特。在这个模式的基础上，我们会进行研究， 确定脂质成分、FFA结构和电荷状态如何影响 模型的内禀速率常数。而试验性的 使用荧光FFA进行这些研究所需的技术代表 作为我们以前工作的直接扩展，新方法将是 为类似的天然FFA研究而开发。

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.