Watts C
EMBO J. 1984 Sep;3(9):1965-70. doi: 10.1002/j.1460-2075.1984.tb02077.x.
Asialoorosomucoid was conjugated to lactoperoxidase and bound specifically to the asialoglycoprotein receptor on the human cell line Hep G2 at 4 degrees C. The bound conjugates incorporated 125I into cell surface proteins in the presence of H2O2. When Hep G2 cells were allowed to endocytose the prebound conjugates by warming to 37 degrees C for 10 min or were incubated for 1 h at 23 degrees C in the presence of conjugate, addition of 125I and H2O2 at 4 degrees C now resulted in labelling of endocytic vesicle proteins. The cell surface labelling pattern and the endosome labelling pattern were compared and found to be distinct. A major component labelled by the endocytosed asialoorosomucoid conjugate is shown to be the transferrin receptor. This protein and a component of 230 000 daltons are enriched in the endosome relative to the cell surface. The endocytosed lactoperoxidase conjugate was also visualised at the morphological level. Characteristic endosome tubules and vesicles contained electron-dense peroxidase reaction product as did cell surface coated pits. Selective capture of some cell surface proteins but not others by coated pits presumably gives rise to the distinct polypeptide composition of the endosome.
将去唾液酸血清类黏蛋白与乳过氧化物酶偶联，并在4℃下使其与人肝癌细胞系Hep G2上的去唾液酸糖蛋白受体特异性结合。在过氧化氢存在的情况下，结合的偶联物将125I掺入细胞表面蛋白中。当将Hep G2细胞升温至37℃ 10分钟，使其内吞预先结合的偶联物，或者在偶联物存在的情况下于23℃孵育1小时后，此时在4℃加入125I和过氧化氢会导致内吞小泡蛋白被标记。对细胞表面标记模式和内体标记模式进行比较，发现二者不同。结果显示，被内吞的去唾液酸血清类黏蛋白偶联物标记的一种主要成分是转铁蛋白受体。相对于细胞表面，这种蛋白和一种230 000道尔顿的成分在内体中更为富集。在形态学水平上也观察到了内吞的乳过氧化物酶偶联物。特征性的内体小管和小泡含有电子致密的过氧化物酶反应产物，细胞表面的被膜小窝也是如此。被膜小窝对某些细胞表面蛋白而非其他蛋白的选择性捕获可能导致了内体独特的多肽组成。
