The C5b-6 complex: formation, isolation, and inhibition of its activity by lipoprotein and the S-protein of human serum.
The C5b-6 complex: formation, isolation, and inhibition of its activity by lipoprotein and the S-protein of human serum.
复制标题
C5b-6 复合物：脂蛋白和人血清 S 蛋白的形成、分离和对其活性的抑制。
作者：
E. Podack;W. P. Kolb;H. Müller
C5b-6复合体是由C7耗尽的血清活化生成的，根据其溶血活性纯化了1200倍。一个均相的双分子络合物，S速率为11.5秒，相对分子质量。共获得32.8万道尔顿。电泳迁移率为-3.4×10-5cm2/伏特秒。未还原的亚基组成有两条蛋白质带：C5b(180,000)和C6(120,000)，还原后有三个亚基：C6(128,000)，C5bα(122,000)和C5β(75,000)。免疫化学分析证实C5b和C6之间形成了复合体，并显示存在SC5b-9复合体表达的两种新抗原之一。60毫微克的C5b-6代表108个溶血有效分子。根据放射性标记的C5b-6的摄取计算出每个溶血事件12到20个C5b-6细胞结合复合体的溶血效率。C5b-6的溶血效率与细胞浓度有关。
血清低密度脂蛋白和S蛋白对C5b-6启动的溶血有强烈的抑制作用，抑制常数分别为34微克/毫升和39微克/毫升。脂蛋白和S蛋白与新生C5b-7形成稳定的、不具溶血活性的复合体。C5b-7的抑制机制被解释为靶细胞膜与抑制物竞争新生C5b-7的瞬时结合部位。
C5b-6 complex was generated by activation of C7-depleted serum and purified 1200-fold based on its hemolytic activity. A homogeneous bimolecular complex with an s-rate of 11.5S and a m.w. of 328,000 daltons was obtained. The electrophoretic mobility was -3.4 × 10-5 cm2/volt sec. The subunit composition as revealed by SDS-polyacrylamide electrophoresis without reduction showed two protein bands: C5b (180,000) and C6 (120,000); and with reduction three subunits: C6 (128,000), C5bα (122,000), and C5β (75,000). Immunochemical analysis confirmed complex formation between C5b and C6 and showed the presence of one of the two neoantigens expressed by the SC5b-9 complex. Sixty nanograms of C5b-6 represented 108 hemolytically effective molecules. A hemolytic efficiency of 12 to 20 C5b-6 cell-bound complexes per lytic event was calculated from the uptake of radiolabeled C5b-6. The hemolytic efficiency of C5b-6 is dependent on the cell concentration.
C5b-6-initiated lysis is strongly inhibited by serum low density lipoproteins with an inhibition constant of Ki = 34 µg/ml and by the S-protein with Ki = 39 µg/ml. Lipoproteins and S-protein form a stable, hemolytically inactive complex with nascent C5b-7. The mechanism of C5b-7 inhibition is interpreted as a competition reaction between the target cell membrane and the inhibitors for the transitory binding site in nascent C5b-7.