Morton R E, Parks J S
Department of Cell Biology, Cleveland Clinic Foundation, OH 44195, USA.
J Lipid Res. 1996 Sep;37(9):1915-23.
Previous studies have shown that lipid transfer protein (LTP) activity is strongly temperature dependent, demonstrating a dramatic rise in activity near 37 degrees C. We have investigated the origin of this rapid rise in LTP activity. LTP-mediated transfers of radiolabeled cholesteryl ester (CE) from LDL to HDL, HDL to LDL, LDL to biotin-LDL, HDL to biotin-HDL, and between liposomes were determined as a function of assay temperature. Only assays containing LDL demonstrated this rapid rise in CE transfer activity. In contrast, TG transfer was almost linear with assay temperature. As human LDL CE undergoes a thermal phase transition near 37 degrees C, we investigated whether the rapid rise in CE transfer was dependent on this transition. Monkey LDL were isolated from animals consuming diets containing cholesterol and enriched in saturated, monounsaturated, or polyunsaturated fatty acids. With these LDL as substrate, the CE transfer between 21 degrees and 49 degrees C could be described by two straight lines, the intersection of which defined the inflection temperature. Among eight LDL samples, the inflection temperature was highly correlated with the CE phase transition determined by differential scanning calorimetry (r2 = 0.86). Both calorimetry and CE transfer activity inflection values were correlated with the saturated + monoene/polyene ratio of the LDL cholesteryl esters (r2 = 0.733 and 0.612, respectively). For LDL with inflection temperatures below 37 degrees C, CE transfer activity at 37 degrees C increased 10-14% for each 1 degree C decrease in the inflection temperature. We conclude that LTP activity is markedly affected by the physical state of the core CE. Diets rich in saturated fatty acids may result in LDL that are poor LTP substrates, which may hinder LTP's ability to promote normal lipoprotein remodeling.
先前的研究表明，脂质转移蛋白（LTP）的活性强烈依赖于温度，在37摄氏度左右活性会急剧上升。我们已经研究了LTP活性这种快速上升的起源。测定了LTP介导的放射性标记胆固醇酯（CE）从低密度脂蛋白（LDL）转移至高密度脂蛋白（HDL）、从HDL转移至LDL、从LDL转移至生物素-LDL、从HDL转移至生物素-HDL以及在脂质体之间转移的情况，作为测定温度的函数。只有含有LDL的测定显示出CE转移活性的这种快速上升。相比之下，甘油三酯（TG）转移与测定温度几乎呈线性关系。由于人LDL CE在37摄氏度左右会发生热相变，我们研究了CE转移的快速上升是否依赖于这种相变。从食用含胆固醇且富含饱和、单不饱和或多不饱和脂肪酸饮食的动物中分离出猴LDL。以这些LDL为底物，21摄氏度至49摄氏度之间的CE转移可用两条直线来描述，其交点定义了转折温度。在八个LDL样本中，转折温度与通过差示扫描量热法测定的CE相变高度相关（r2 = 0.86）。量热法和CE转移活性转折值均与LDL胆固醇酯的饱和 + 单烯/多烯比率相关（分别为r2 = 0.733和0.612）。对于转折温度低于37摄氏度的LDL，转折温度每降低1摄氏度，37摄氏度时的CE转移活性就会增加10 - 14%。我们得出结论，LTP活性受到核心CE物理状态的显著影响。富含饱和脂肪酸的饮食可能导致LDL成为较差的LTP底物，这可能会阻碍LTP促进正常脂蛋白重塑的能力。
