Dautry-Varsat A, Ciechanover A, Lodish H F
Proc Natl Acad Sci U S A. 1983 Apr;80(8):2258-62. doi: 10.1073/pnas.80.8.2258.
At pH 5.4 apotransferrin (iron-free transferrin) binds to cell-surface transferrin receptors to the same extent and with the same affinity as does diferric transferrin at pH 7.0. Apotransferrin is quickly dissociated from its receptor when the pH is raised to 7.0. These and other results strongly support a simple model that explains the cycling of transferrin during a single cycle of receptor-mediated endocytosis. Diferric transferrin binds to cell-surface receptors, and the transferrin-receptor complex is endocytosed. The pH of the endocytic vesicle is lowered to 5.5 or below; this causes dissociation of iron from the transferrin-receptor complex, but apotransferrin remains bound to its receptor. The iron remains within the cell, and the apotransferrin-receptor complex is recycled to the cell surface. Upon encountering the neutral pH of the medium, apotransferrin is dissociated from the cell.
在pH 5.4时，脱铁转铁蛋白（无铁转铁蛋白）与细胞表面转铁蛋白受体的结合程度和亲和力与pH 7.0时的双铁转铁蛋白相同。当pH值升至7.0时，脱铁转铁蛋白会迅速从其受体上解离。这些以及其他结果有力地支持了一个简单模型，该模型解释了转铁蛋白在受体介导的内吞作用的单个循环中的循环过程。双铁转铁蛋白与细胞表面受体结合，转铁蛋白 - 受体复合物被内吞。内吞小泡的pH值降至5.5或更低；这导致铁从转铁蛋白 - 受体复合物中解离，但脱铁转铁蛋白仍与其受体结合。铁保留在细胞内，脱铁转铁蛋白 - 受体复合物被循环回到细胞表面。一旦遇到中性pH的培养基，脱铁转铁蛋白就会从细胞上解离。
