Jonas A, Kézdy K E, Williams M I, Rye K A
Department of Biochemistry, College of Medicine at Urbana-Champaign, University of Illinois 61801.
J Lipid Res. 1988 Oct;29(10):1349-57.
In this study we examined the transfer of lipids between reconstituted high density lipoprotein discs (r-HDL) and human low density lipoproteins (LDL) in the presence and absence of lecithin:cholesterol acyltransferase (LCAT) or of plasma phospholipid transfer protein (PLTP). We found that spontaneous transfer of phospholipids from r-HDL to LDL occurred by an apparent first order reaction with a half-time of 5.8 to 6.9 hr depending on the phospholipid. During the time of incubation of r-HDL with LDL (from 0 to 25 hr), the phospholipid content of r-HDL decreased more than 30%, the free cholesterol content increased 2.5-fold, and low levels of cholesteryl esters appeared in r-HDL. These compositional changes gave rise to small discoidal particles with a limiting diameter of 77 A and two molecules of apoA-I per particle. When LCAT was included in the reaction mixture, the r-HDL lost even more phospholipid, lost some free cholesterol, and gained cholesteryl esters relative to the apolipoprotein content, due to the enzymatic reaction. The products of the LCAT reaction had a diameter of 93 A and three, rather than two, apoA-I molecules per particle. Inclusion of PLTP into the reaction mixture accelerated the transfer of phospholipids (half-time of 1.7 hr) and the formation of the 77 A product. In addition to these compositional and morphological changes, which may be important in the interconversions of native HDL subspecies, the prolonged incubations revealed some slow reactions, such as the esterification of LDL cholesterol by LCAT, a background formation of cholesteryl esters in r-HDL, and an apparent hydrolysis of cholesteryl esters in LDL in the presence of r-HDL.
在本研究中，我们检测了在有或没有卵磷脂胆固醇酰基转移酶（LCAT）或血浆磷脂转运蛋白（PLTP）存在的情况下，重组高密度脂蛋白圆盘（r-HDL）与人低密度脂蛋白（LDL）之间的脂质转移。我们发现，磷脂从r-HDL自发转移至LDL是通过明显的一级反应发生的，半衰期为5.8至6.9小时，具体取决于磷脂种类。在r-HDL与LDL孵育期间（从0至25小时），r-HDL的磷脂含量下降超过30%，游离胆固醇含量增加2.5倍，并且r-HDL中出现了低水平的胆固醇酯。这些成分变化产生了直径限制为77 Å且每个颗粒含有两个载脂蛋白A-I分子的小圆盘状颗粒。当反应混合物中加入LCAT时，由于酶促反应，相对于载脂蛋白含量，r-HDL失去了更多的磷脂，失去了一些游离胆固醇，并获得了胆固醇酯。LCAT反应的产物直径为93 Å，每个颗粒含有三个而非两个载脂蛋白A-I分子。在反应混合物中加入PLTP加速了磷脂转移（半衰期为1.7小时）以及77 Å产物的形成。除了这些可能在天然HDL亚类相互转化中起重要作用的成分和形态变化外，长时间孵育还揭示了一些缓慢反应，例如LCAT对LDL胆固醇的酯化、r-HDL中胆固醇酯的背景形成以及在r-HDL存在下LDL中胆固醇酯的明显水解。
