Rifici V A, Eder H A
J Biol Chem. 1984 Nov 25;259(22):13814-8.
Apolipoprotein (apo) E-deficient rat high-density lipoproteins (HDL) bind to isolated rat hepatocytes at 4 degrees C by a process shown to be saturable and competed for by an excess of unlabeled HDL. Uptake (binding and internalization) at 37 degrees C was also saturable and competed for by an excess of unlabeled HDL. At 37 degrees C the HDL apoprotein was degraded as evidenced by the appearance of trichloroacetic acid-soluble radioactivity in the incubation media. The binding of a constant amount of 125I-apo-E-deficient HDL was measured in the presence of increasing concentrations of various lipoproteins. HDL and dimyristoyl phosphatidylcholine (DMPC) X apo-A-I complexes decreased binding by 80 and 65%, respectively. Human low-density lipoproteins, DMPC X apo-E complexes, and DMPC vesicles alone did not compete for apo-E-deficient HDL binding. However, DMPC X apo-E complexes did compete for the binding of the total HDL fraction that contained apo-E but to a lesser extent than did DMPC X apo-A-I. DMPC X 125I-apo-A-I complexes also bound to hepatocytes, and this binding was competed for by excess HDL (70%) and DMPC X apo-A-I complexes (65%), but there was no competition for binding by DMPC vesicles or DMPC X apo-E complexes. It thus appears that hepatocytes have a specific receptor for HDL and that apo-A-I is the ligand for this receptor.
载脂蛋白（apo）E缺陷大鼠的高密度脂蛋白（HDL）在4℃时通过一种可饱和的过程与分离的大鼠肝细胞结合，且未标记的过量HDL可与之竞争。在37℃时的摄取（结合和内化）也是可饱和的，未标记的过量HDL也可与之竞争。在37℃时，HDL载脂蛋白会发生降解，这可通过孵育培养基中出现三氯乙酸可溶性放射性来证明。在存在不同浓度递增的各种脂蛋白的情况下，测定了恒定数量的125I-apo-E缺陷HDL的结合情况。HDL和二肉豆蔻酰磷脂酰胆碱（DMPC）×apo-A-I复合物分别使结合减少了80%和65%。人低密度脂蛋白、DMPC×apo-E复合物以及单独的DMPC囊泡均不竞争apo-E缺陷HDL的结合。然而，DMPC×apo-E复合物确实竞争含有apo-E的总HDL部分的结合，但程度小于DMPC×apo-A-I。DMPC×125I-apo-A-I复合物也与肝细胞结合，这种结合可被过量HDL（70%）和DMPC×apo-A-I复合物（65%）竞争，但DMPC囊泡或DMPC×apo-E复合物不竞争结合。因此，肝细胞似乎具有HDL的特异性受体，且apo-A-I是该受体的配体。
