Strong P N, Evans W H
Eur J Biochem. 1987 Mar 2;163(2):267-73. doi: 10.1111/j.1432-1033.1987.tb10797.x.
The binding and uptake of the bee venom toxin apamin, by guinea-pig and rat liver were studied. Guinea-pig liver plasma membranes contain inhibitable, high-affinity binding sites for [125I]monoiodoapamin: Kd = 12.6 +/- 0.8 pM (SE); Bmax = 4.2 +/- 0.2 fmol/mg protein. No binding sites for [125I]monoiodoapamin on rat liver plasma membranes were detected in agreement with the absence of a physiological response to the toxin by rat hepatocytes. [125I]Monoiodoapamin, injected into the portal vein of guinea-pigs, was recovered in an undegraded form in a liver endosome fraction. The uptake of [125I]monoiodoapamin by rat livers was less than 4% of that taken up by guinea-pig livers and there was little evidence of radiolabelled toxin appearing in isolated rat endocytic vesicles. Inhibitable, high-affinity binding sites for [125I]monoiodoapamin were also identified on isolated guinea-pig liver endosomal membranes; Kd = 10.6 +/- 3.3 pM; Bmax = 2.5 +/- 0.6 fmol/mg protein. No inhibitable apamin binding sites were detected on rat endosomal membranes. Plasma membranes and endosomal membranes isolated from guinea-pig liver showed a similar spectrum of polypeptides to that previously reported for plasma membranes and endosomal membranes isolated from rat liver. The enzymatic composition of guinea-pig endosomes was also similar to that previously reported for rat endosomes. The results indicate that apamin was internalised by receptor-mediated endocytosis by guinea-pig liver cells in an analogous manner to that already shown for a variety of endogenous ligands.
研究了蜂毒毒素蜂毒明肽在豚鼠和大鼠肝脏中的结合与摄取情况。豚鼠肝脏质膜含有可抑制的、对[¹²⁵I]单碘蜂毒明肽具有高亲和力的结合位点：解离常数（Kd）= 12.6 ± 0.8皮摩尔（标准误）；最大结合容量（Bmax）= 4.2 ± 0.2飞摩尔/毫克蛋白质。未在大鼠肝脏质膜上检测到[¹²⁵I]单碘蜂毒明肽的结合位点，这与大鼠肝细胞对该毒素无生理反应相一致。注入豚鼠门静脉的[¹²⁵I]单碘蜂毒明肽，以未降解形式在肝脏内体部分中被回收。大鼠肝脏对[¹²⁵I]单碘蜂毒明肽的摄取量不到豚鼠肝脏摄取量的4%，且几乎没有证据表明放射性标记毒素出现在分离的大鼠内吞小泡中。在分离的豚鼠肝脏内体膜上也鉴定出了对[¹²⁵I]单碘蜂毒明肽具有可抑制的、高亲和力的结合位点；Kd = 10.6 ± 3.3皮摩尔；Bmax = 2.5 ± 0.6飞摩尔/毫克蛋白质。在大鼠内体膜上未检测到可抑制的蜂毒明肽结合位点。从豚鼠肝脏分离的质膜和内体膜显示出与先前报道的从大鼠肝脏分离的质膜和内体膜相似的多肽谱。豚鼠内体的酶组成也与先前报道的大鼠内体相似。结果表明，蜂毒明肽被豚鼠肝细胞通过受体介导的内吞作用内化，其方式与已显示的多种内源性配体的内化方式类似。
