Klausner R D, Ashwell G, van Renswoude J, Harford J B, Bridges K R
Proc Natl Acad Sci U S A. 1983 Apr;80(8):2263-6. doi: 10.1073/pnas.80.8.2263.
The binding of apotransferrin to the transferrin receptor on the surface of human leukemic K562 cells was found to be significantly less tight than that of the holoprotein, diferric transferrin. The finding that both ligands displayed linear Scatchard plots with similar receptor number (approximately equal to 150,000 per cell) and mutually inhibit each other's binding suggested that they bind to the same receptor. Both the dissociation and association rate of apotransferrin were markedly increased (28-fold and 15-fold, respectively) at pH 7.2 compared to pH 4.8. Using the values of these binding parameters, we propose a mechanism to account for the recycling of transferrin subsequent to internalization and residence within an acidic nonlysosomal organelle where iron is removed.
研究发现，脱铁转铁蛋白与人白血病K562细胞表面转铁蛋白受体的结合明显不如全蛋白——双铁转铁蛋白紧密。两种配体均显示出线性Scatchard图，受体数量相似（约为每个细胞150,000个），且相互抑制彼此的结合，这一发现表明它们与同一受体结合。与pH 4.8相比，在pH 7.2时，脱铁转铁蛋白的解离速率和结合速率均显著增加（分别为28倍和15倍）。利用这些结合参数的值，我们提出了一种机制，以解释转铁蛋白在被内化并存在于去除铁的酸性非溶酶体细胞器后如何进行循环利用。
