Purification and characterization of LDL containing apo B-48 from the plasma of an apo E-deficient patient

据报道，载脂蛋白（apo）E缺乏患者的血浆低密度脂蛋白（LDL）含有apo B-48（D. Kurophilet al.（1991）Atheroscler.88，15），它是乳糜微粒的结构蛋白，不存在于正常受试者的空腹血浆LDL中。我们用肝素-琼脂糖柱层析法从该患者血浆中分离出含载脂蛋白B-48（apo B-48 LDL）和载脂蛋白B-100（apo B-100 LDL）的LDL。除apo B-48外，apo B-48 LDL还含有apo A-I、apo A-IV和apo Cs。载脂蛋白B-48和载脂蛋白B-100 LDL的大小和脂质组成仅有轻微差异，两者均含有比正常受试者LDL更多的甘油三酯。与载脂蛋白E孵育后，载脂蛋白B-48低密度脂蛋白中载脂蛋白E的含量是载脂蛋白B-100低密度脂蛋白的两倍，载脂蛋白A-I和载脂蛋白A-IV的含量显著降低。这些结果表明，正常受试者中含有载脂蛋白B-48的脂蛋白在接受载脂蛋白E以交换载脂蛋白A-I和A-IV后，可通过载脂蛋白E介导的受体机制快速摄取。

The plasma low density lipoprotein (LDL) of an apoprotein (apo) E-deficient patient was reported to contain apo B-48 (D.Kurosaka et al. (1991) Atheroscler.88,15), which is a structural protein of chylomicrons and is not present in the fasting plasma LDL of normal subjects. We separated the LDL containing apo B-48 (apo B-48 LDL) and apo B-100 (apo B-100 LDL) from the plasma of this patient using heparin-Sepharose column chromatography. The apo B-48 LDL contained apo A-I,apo A-IV,and apo Cs besides apo B-48. There were only slight differences in size and lipid composition of the apo B-48 and the apo B-100 LDLs, both of which contained more triglyceride than LDL from normal subjects. After incubation with apo E,the apo B-48 LDL contained twice the amount of apo E than the apo B-100 LDL and showed a marked decrease in apo A-I and apo A-IV content. These results suggest that lipoproteins containing apo B-48 in normal subjects can be quickly taken up through an apo E-mediated receptor mechanism after receiving apo E in exchange for apo A-I and A-IV.