Morgan E H
Biochim Biophys Acta. 1983 Jul 14;762(4):498-502. doi: 10.1016/0167-4889(83)90052-6.
The effect of pH on the binding of apotransferrin and diferric transferrin to reticulocyte membrane receptors was investigated using rabbit transferrin and rabbit reticulocyte ghosts, intact cells and a detergent-solubilized extract of reticulocyte membranes. The studies were performed within the pH range 4.5-8.0. The binding of apotransferrin to ghosts and membrane extracts and its uptake by intact reticulocytes was high at pH levels below 6.5 but decreased to very low values as the pH was raised above 6.5. By contrast, diferric transferrin showed a high level of binding and uptake between pH 7.0 and 8.0 in addition to binding only slightly less than did apotransferrin at pH values below 6.5. It is proposed that the high affinity of apotransferrin for its receptor at lower pH values and low affinity at pH 7.0 or above allow transferrin to remain bound to the receptor when it is within acidic intracellular vesicles, even after loss of its iron, but also allow ready release from the cell membrane when it is exteriorized by exocytosis after iron uptake. The binding of transferrin to the receptor throughout the endocytosis-exocytosis cycle may protect it from proteolytic breakdown and aid in its recycling to the outer cell membrane.
利用兔转铁蛋白、兔网织红细胞空泡、完整细胞以及网织红细胞膜的去污剂溶解提取物，研究了pH对脱铁转铁蛋白和双铁转铁蛋白与网织红细胞膜受体结合的影响。研究在pH值4.5 - 8.0范围内进行。在pH值低于6.5时，脱铁转铁蛋白与空泡和膜提取物的结合以及其被完整网织红细胞摄取的水平较高，但当pH值升至6.5以上时，其水平降至非常低的值。相比之下，双铁转铁蛋白在pH 7.0至8.0之间表现出高水平的结合和摄取，此外在pH值低于6.5时其结合仅略低于脱铁转铁蛋白。有人提出，脱铁转铁蛋白在较低pH值下对其受体具有高亲和力，而在pH 7.0或更高时具有低亲和力，这使得转铁蛋白在进入酸性细胞内小泡时，即使失去铁后仍能与受体结合，但在摄取铁后通过胞吐作用排出细胞外时也能从细胞膜上轻易释放。在整个内吞 - 外排循环中，转铁蛋白与受体的结合可能保护其免受蛋白水解破坏，并有助于其循环回到细胞外膜。
