Cooper A D, Erickson S K, Nutik R, Shrewsbury M A
J Lipid Res. 1982 Jan;23(1):42-52.
The binding of chylomicron remnants to rat liver membranes was investigated using radioiodinated lipoproteins. The specific activity of binding increased in parallel with increased enrichment in plasma membrane markers. The yield of receptor activity, however, decreased with enrichment. Accordingly, a partially purified plasma membrane preparation was used for routine studies. Binding was saturable, with half maximal binding achieved at 4.6 micro g tetramethylurea-precipitable protein per ml. The rate of binding was time- and temperature-dependent. It could be inhibited only moderately by 10 mM EDTA. Chylomicron remnants appeared to bind to the membrane as a unit. The bound particle was richer in apoproteins of 20,000-50,000 molecular weight relative to low molecular weight apoproteins than the particles that were not bound. Lipoprotein particles containing only human apoB did not bind to liver membranes nor did they compete for the remnant binding site. Rat lipoproteins of d 1.019-1.063 g/ml did compete for remnant binding. When they were separated into apoB-rich (LDL) or apoE-rich (HDL(c)) fractions by block electrophoresis, the apoE-rich fraction was a more potent competitor. ApoE purified and reconstituted into dimyristoyl phosphatidylcholine vesicles was a potent competitor for the remnant binding site. Vesicles containing (125)I-labeled apoE bound to the membranes, and they could be displaced by unlabeled remnants. Dimyristoyl phosphatidylcholine vesicles themselves did not compete with either remnants or apoE-phospholipid vesicles. These results offer strong support for the hypothesis that the liver membrane chylomicron remnant receptor recognizes apoE with a high affinity, and this initiates the rapid removal of lipoproteins that contain this apoprotein.-Cooper, A. D., S. K. Erickson, R. Nutik, and M. A. Shrewsbury. Characterization of chylomicron remnant binding to rat liver membranes.
使用放射性碘化脂蛋白研究了乳糜微粒残粒与大鼠肝细胞膜的结合。结合的比活性随质膜标志物富集程度的增加而平行增加。然而，受体活性的产量随富集程度降低。因此，使用部分纯化的质膜制剂进行常规研究。结合是可饱和的，每毫升4.6微克四甲基脲可沉淀蛋白时达到半数最大结合。结合速率与时间和温度有关。10 mM乙二胺四乙酸（EDTA）仅能适度抑制它。乳糜微粒残粒似乎作为一个整体与膜结合。相对于未结合的颗粒，结合的颗粒富含分子量为20,000 - 50,000的载脂蛋白，而低分子量载脂蛋白较少。仅含人载脂蛋白B的脂蛋白颗粒不与肝细胞膜结合，也不竞争残粒结合位点。密度为1.019 - 1.063 g/ml的大鼠脂蛋白确实竞争残粒结合。当通过区带电泳将它们分离为富含载脂蛋白B的（低密度脂蛋白，LDL）或富含载脂蛋白E的（高密度脂蛋白(c)，HDL(c)）组分时，富含载脂蛋白E的组分是更强的竞争者。纯化并重构到二肉豆蔻酰磷脂酰胆碱囊泡中的载脂蛋白E是残粒结合位点的强竞争者。含有(125)I标记载脂蛋白E的囊泡与膜结合，并且它们可被未标记的残粒取代。二肉豆蔻酰磷脂酰胆碱囊泡本身不与残粒或载脂蛋白E - 磷脂囊泡竞争。这些结果为肝细胞膜乳糜微粒残粒受体以高亲和力识别载脂蛋白E这一假说提供了有力支持，并且这启动了含这种载脂蛋白的脂蛋白的快速清除。 - 库珀，A.D.，S.K.埃里克森，R.努蒂克，和M.A.施鲁斯伯里。乳糜微粒残粒与大鼠肝细胞膜结合的特性。
