Trieu V N, McConathy W J
Lipoprotein and Atherosclerosis Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104.
Biochemistry. 1990 Jun 26;29(25):5919-24. doi: 10.1021/bi00477a006.
A method combining ligand dot blotting and digital imaging was used to determine the apparent dissociation constant (KD) for the binding of lipoprotein(a) to low-density lipoproteins (Lp(a)-LDL2). By use of this approach, the KD for the Lp(a)-LDL2 complex was shown to be in the nanomolar range [(1.05 +/- 0.21) x 10(-8) M, n = 4]. The Lp(a)-LDL2 interaction was both hydrophobic and ionic; however, hydrophobic forces predominated because the interaction was demonstrable at high salt concentration (greater than 2 M NaCl), while no complex was detectable at low salt concentration (less than 0.08 M NaCl). Consistent with the hydrophobic nature of this interaction, the Lp(a)-LDL2 complex was stable over a wide pH range (4-10). Plasminogen did not compete with Lp(a) binding to LDL2 even at a 2.2 X 10(3) molar excess of plasminogen over the LDL2 concentration. The only component identified in plasma and serum that inhibited the binding of LDL2 to Lp(a) was apolipoprotein B containing lipoproteins (apoB-Lp). These studies indicate that the Lp(a)-LDL2 complex could exist in plasma. In fact, up to 72% of purified Lp(a) added to an Lp(a)-negative hypertriglyceridemic plasma floated with apoB-Lp (d less than 1.063 g/mL) following ultracentrifugation, whereas only 9% of the purified Lp(a) added to the apoB-Lp-free 1.12 g/mL infranate floated at d less than 1.063 g/mL. The formation of a complex of Lp(a) with apoB-Lp could increase the amount of cholesterol ester bound per cellular receptor, e.g., LDL receptor, and thus potentially accelerate cholesterol removal from the vascular compartment.
采用配体斑点印迹法和数字成像相结合的方法测定脂蛋白(a)与低密度脂蛋白（Lp(a)-LDL2）结合的表观解离常数（KD）。通过这种方法，Lp(a)-LDL2复合物的KD显示在纳摩尔范围内[（1.05±0.21）×10⁻⁸ M，n = 4]。Lp(a)-LDL2相互作用既有疏水性又有离子性；然而，疏水力占主导，因为在高盐浓度（大于2 M NaCl）下该相互作用可被证实，而在低盐浓度（小于0.08 M NaCl）下未检测到复合物。与这种相互作用的疏水性一致，Lp(a)-LDL2复合物在较宽的pH范围（4 - 10）内稳定。即使纤溶酶原浓度比LDL2浓度高2.2×10³倍，纤溶酶原也不会与Lp(a)竞争结合LDL2。在血浆和血清中鉴定出的唯一抑制LDL2与Lp(a)结合的成分是含载脂蛋白B的脂蛋白（apoB-Lp）。这些研究表明Lp(a)-LDL2复合物可能存在于血浆中。事实上，添加到Lp(a)阴性的高甘油三酯血症血浆中的纯化Lp(a)，在超速离心后，高达72%与apoB-Lp（d小于1.063 g/mL）一起漂浮，而添加到无apoB-Lp的1.12 g/mL下层液中的纯化Lp(a)，只有9%在d小于1.063 g/mL时漂浮。Lp(a)与apoB-Lp形成复合物可能会增加每个细胞受体（如LDL受体）结合的胆固醇酯量，从而有可能加速从血管腔室中清除胆固醇。
