Tall A R, Green P H
J Biol Chem. 1981 Feb 25;256(4):2035-44.
Incubation of phosphatidylcholine vesicles with isolated high density lipoproteins (HDL) or with whole plasma results in transfer of phospholipid into HDL. To investigate the mechanisms of this process, small unilamellar vesicles of egg phosphatidylcholine were incubated with human HDL3 (d 1.125 to 1.210 g/ml) or with plasma and were subsequently analyzed by density gradient ultracentrifugation and negative stain electron microscopy. Incubation of vesicles with isolated HDL3 resulted in formation of both discoidal lipoproteins (1.04 to 1.06 g/ml) and phospholipid-enriched spherical lipoproteins (1.10 to 1.14 g/ml). The lipid bilayer discoidal lipoproteins had dimensions approximately 22 X 5.4 nm and contained phospholipid, apoA-I, and apoA-II. The phospholipid-enriched sperical HDL were increased in diameter and decreased in density compared to HDL3. With maximum phospholipid uptake these lipoproteins had a similar density, size, and lipid composition to HDL2a, a phospholipid-rich subfraction of HDL isolated from human plasma between 1.100 to 1.125 g/ml. Scanning microcalorimetry of the phospholipid-enriched HDL showed, compared to HDL3, a decrease in the temperature and enthalpy of lipoprotein denaturation. This altered denaturation pattern was similar to that of plasma HDL2a. Following incubation of vesicles in plasma, there was an increase in phospholipid-rich lipoproteins within the HDL2 density range (1.070 to 1.125 g/ml), and disappearance of lipoproteins from the HDL3 density range (1.125 to 1.210 g/ml). The phospholipid-rich HDL2 contained a major peak (d 1.095 to 1.125 g/ml), which consisted of only spherical particles and a smaller peak (d 1.070 to 1.095 g/ml), which included a population of lipid bilayer discs. Thus, during incubation of vesicles with isolated HDL3, there is insertion of phospholipid into HDL3, producing spherical lipoproteins which have some properties in common with HDL2a. Discoidal lipoproteins are also formed, probably as a result of interaction of vesicles with small amounts of apoA-I and apoA-II released from HDL3. The uptake of phosphatidylcholine by HDL in whole plasma occurs by similar mechanisms.
将磷脂酰胆碱囊泡与分离出的高密度脂蛋白（HDL）或全血浆一起温育，会导致磷脂转移到HDL中。为了研究这一过程的机制，将鸡蛋磷脂酰胆碱的小单层囊泡与人HDL3（密度为1.125至1.210 g/ml）或血浆一起温育，随后通过密度梯度超速离心和负染电子显微镜进行分析。将囊泡与分离出的HDL3温育导致形成盘状脂蛋白（密度为1.04至1.06 g/ml）和富含磷脂的球形脂蛋白（密度为1.10至1.14 g/ml）。脂质双层盘状脂蛋白的尺寸约为22×5.4 nm，含有磷脂、载脂蛋白A-I和载脂蛋白A-II。与HDL3相比，富含磷脂的球形HDL直径增加而密度降低。在最大程度摄取磷脂时，这些脂蛋白在密度、大小和脂质组成上与HDL2a相似，HDL2a是从人血浆中分离出的密度在1.100至1.125 g/ml之间的富含磷脂的亚组分。与HDL3相比，对富含磷脂的HDL进行扫描量热法显示脂蛋白变性的温度和焓降低。这种改变的变性模式与血浆HDL2a的相似。在血浆中温育囊泡后，HDL2密度范围（1.070至1.125 g/ml）内富含磷脂的脂蛋白增加，而HDL3密度范围（1.125至1.210 g/ml）内的脂蛋白消失。富含磷脂的HDL2包含一个主要峰（密度为1.095至1.125 g/ml），其仅由球形颗粒组成，还有一个较小的峰（密度为1.070至1.095 g/ml），其中包括一群脂质双层盘。因此，在将囊泡与分离出的HDL3温育期间，磷脂插入HDL3中，产生具有一些与HDL2a共同特性的球形脂蛋白。盘状脂蛋白也会形成，可能是囊泡与从HDL3释放的少量载脂蛋白A-I和载脂蛋白A-II相互作用的结果。HDL在全血浆中摄取磷脂酰胆碱的过程通过类似的机制发生。
