Noy N, Donnelly T M, Zakim D
Biochemistry. 1986 Apr 22;25(8):2013-21. doi: 10.1021/bi00356a027.
The spontaneous transfer of water-insoluble substances from plasma to the interior of cells would involve a series of steps in which the substance of interest dissociates from albumin in plasma, enters the outer half of the plasma membrane of a cell, crosses the bilayer, and then dissociates from the inner half of the plasma membrane to enter cell cytosol and diffuses to sites of its metabolism. We have examined the behavior of long-chain fatty acids in the uptake process, assuming that none of these steps is facilitated by the cell during the entry of fatty acids into the liver. Comparison of the spontaneous rates for each individual step with rates of uptake of fatty acid by perfused liver leads to the conclusion that the uptake of fatty acids is not limited by kinetic factors but is determined instead by the equilibrium distribution (Keq) of fatty acids between albumin in plasma and the phospholipids of the plasma membrane. This idea was examined further by determining whether there was a relationship between the value for Keq and rates of uptake of a fatty acid and the pattern of kinetics for uptake. The data indicate that there is a linear relationship between Keq and the rate of uptake, that uptake rates can be predicted with a high degree of accuracy from thermodynamic data, and that the pattern of kinetics of uptake is compatible with the idea that the uptake rate is determined by the relative affinity of a fatty acid for albumin and membranes.
水不溶性物质从血浆自发转移至细胞内部将涉及一系列步骤，其中，目标物质在血浆中与白蛋白解离，进入细胞的质膜外半层，穿过双层膜，然后从质膜内半层解离，进入细胞胞质溶胶并扩散至其代谢位点。我们研究了长链脂肪酸在摄取过程中的行为，假设在脂肪酸进入肝脏的过程中，这些步骤均未得到细胞的促进。将每个步骤的自发速率与灌注肝脏摄取脂肪酸的速率进行比较，得出的结论是，脂肪酸的摄取不受动力学因素限制，而是由脂肪酸在血浆白蛋白和质膜磷脂之间的平衡分布（Keq）决定。通过确定Keq值与脂肪酸摄取速率以及摄取动力学模式之间是否存在关系，对这一观点进行了进一步研究。数据表明，Keq与摄取速率之间存在线性关系，摄取速率可以根据热力学数据高度准确地预测，并且摄取动力学模式与摄取速率由脂肪酸对白蛋白和膜的相对亲和力决定这一观点相符。
