Blight G D, Morgan E H
Eur J Cell Biol. 1987 Apr;43(2):260-5.
Earlier studies have shown that transferrin binds to specific receptors on the reticulocyte surface, clusters in coated pits and is then internalized via endocytic vesicles. Guinea-pig reticulocytes also have specific receptors for ferritin. In this paper ferritin and transferrin endocytosis by guinea-pig reticulocytes was studied by electron microscopy using the natural electron density of ferritin and colloidal gold-transferrin (AuTf). At 4 degrees C both ligands bound to the cell surface. At 37 degrees C progressive uptake occurred by endocytosis. AuTf and ferritin clustered in the same coated pits and small intracellular vesicles. After 60 min incubations the ligands colocalized to large multivesicular endosomes (MVE), still membrane-bound. MVE subsequently fused with the plasma membrane and released AuTf, ferritin and inclusions by exocytosis. All endocytic structures labelled with AuTf contained ferritin, but 23 to 35% of ferritin-labelled endocytic structures contained no AuTf. These data suggest that ferritin and transferrin are internalized through the same pathway involving receptors, coated pits and vesicles, but that these proteins are recycled only partly in common.
早期研究表明，转铁蛋白与网织红细胞表面的特定受体结合，聚集在被膜小窝中，然后通过内吞小泡被内化。豚鼠网织红细胞也有铁蛋白的特异性受体。在本文中，利用铁蛋白的天然电子密度和胶体金 - 转铁蛋白（AuTf），通过电子显微镜研究了豚鼠网织红细胞对铁蛋白和转铁蛋白的内吞作用。在4℃时，两种配体都与细胞表面结合。在37℃时，通过内吞作用逐渐发生摄取。AuTf和铁蛋白聚集在相同的被膜小窝和小的细胞内小泡中。孵育60分钟后，配体共定位到仍然与膜结合的大型多囊泡内体（MVE）中。MVE随后与质膜融合，并通过胞吐作用释放AuTf、铁蛋白和内含物。所有用AuTf标记的内吞结构都含有铁蛋白，但23%至35%的用铁蛋白标记的内吞结构不含AuTf。这些数据表明，铁蛋白和转铁蛋白通过涉及受体、被膜小窝和小泡的相同途径被内化，但这些蛋白质仅部分共同循环利用。
