Shepherd J, Patsch J R, Packard C J, Gotto A M, Taunton O D
J Lipid Res. 1978 Mar;19(3):383-9.
This study was designed to identify a method for the measurement of human high density lipoprotein subfraction (HDL2 and HDL3) metabolism. Apolipoproteins A-I, A-II, and C, the major HDL apoproteins, were radioiodinated and incorporated individually into HDL2 and HDL3 in vitro. Using a double label technique, the turnover of apoA-I in HDL2 and HDL3 was measured simultaneously in a normal male. The apoprotein exchanged rapidly between the two subfractions, evidenced by equilibration of their apoA-I specific activity. Radiolabeled apoA-II, incorporated into the subfractions, showed a similar exchange in vitro. Incubation of 131I-labeled very low density lipoproteins (VLDL) with HDL or its subfractions resulted in transfer of C proteins from VLDL to the HDL moiety. The extent of transfer was dependent on the HDL subfraction present; 50% of the VLDL apoC was transferred to HDL3, while the transfer to total HDL and HDL2 was 69% and 78%, respectively. ApoC also exchanged between HDL2 and HDL3, again showing a preference for the former and suggesting a primary metabolic relationship between VLDL and HDL2. Overall, the study indicates that apoA-I, apoA-II, and the C proteins exist in equilibrium between HDL2 and HDL3. This phenomenon precludes their use as probes for HDL subfraction metabolism in humans.
本研究旨在确定一种测量人类高密度脂蛋白亚组分（HDL2和HDL3）代谢的方法。主要的HDL载脂蛋白载脂蛋白A-I、A-II和C被放射性碘化，并分别在体外掺入HDL2和HDL3中。使用双标记技术，在一名正常男性中同时测量了HDL2和HDL3中载脂蛋白A-I的周转率。载脂蛋白在两个亚组分之间迅速交换，其载脂蛋白A-I比活性达到平衡证明了这一点。掺入亚组分中的放射性标记载脂蛋白A-II在体外也显示出类似的交换。用131I标记的极低密度脂蛋白（VLDL）与HDL或其亚组分孵育，导致C蛋白从VLDL转移到HDL部分。转移程度取决于存在的HDL亚组分；50%的VLDL载脂蛋白C转移到HDL3，而转移到总HDL和HDL2的比例分别为69%和78%。载脂蛋白C也在HDL2和HDL3之间交换，再次显示出对前者的偏好，并表明VLDL与HDL2之间存在主要的代谢关系。总体而言，该研究表明载脂蛋白A-I、载脂蛋白A-II和C蛋白在HDL2和HDL3之间处于平衡状态。这种现象使得它们不能用作人类HDL亚组分代谢的探针。
