Morley C G, Bezkorovainy A
Clin Physiol Biochem. 1983;1(6):318-28.
The liver serves as a storage organ for iron, 2-5 mg of Fe being exchanged between plasma and liver daily in the human being. Such iron transfer from serotransferrin (TF) to hepatocytes involves a TF receptor. We are reporting some of the properties of this receptor using isolated rat hepatocyte membranes as the receptor source. Iron-saturated 125I-rat TF was used for these studies. Specific versus nonspecific TF binding was evaluated by labelling the membranes with 125I-TF and then displacing specific binding with excess unlabelled TF. A mean residency time of 18-20 min was calculated for the TF on each receptor molecule. There were 31,000 +/- 17,000 receptors/cell with a dissociation constant of 0.3 X 10(-7) mol/l. The binding obeyed simple Michaelis-Menten kinetics. Specifically bound iron-saturated 125I-TF could best be eluted with cold Fe-saturated TF; cold apo- and 50% saturated TFs were less effective. The binding of apo- and 50% saturated TF was much less pronounced than that of Fe-saturated TF. The membrane receptor was moderately heat stable, extractable with detergent, and was trypsin sensitive. Studies with 125I/59Fe-TF and whole cells suggested that Fe-TF is not in a major way internalized during iron uptake. It is concluded that there are TF receptors present on the rat hepatocyte plasma membrane that may have a role in uptake by the cells without internalization of the TF molecule.
肝脏是铁的储存器官，在人类中，血浆和肝脏之间每天有2 - 5毫克的铁进行交换。这种从血清转铁蛋白（TF）到肝细胞的铁转移涉及一种TF受体。我们正在利用分离的大鼠肝细胞膜作为受体来源，报告这种受体的一些特性。铁饱和的125I - 大鼠TF用于这些研究。通过用125I - TF标记膜，然后用过量未标记的TF取代特异性结合来评估特异性与非特异性TF结合。计算出每个受体分子上TF的平均驻留时间为18 - 20分钟。每个细胞有31,000 ± 17,000个受体，解离常数为0.3×10(-7)摩尔/升。结合遵循简单的米氏动力学。特异性结合的铁饱和125I - TF最好用冷的铁饱和TF洗脱；冷的脱铁和50%饱和的TF效果较差。脱铁和50%饱和TF的结合比铁饱和TF的结合要弱得多。膜受体具有中等热稳定性，可用去污剂提取，对胰蛋白酶敏感。用125I/59Fe - TF和全细胞进行的研究表明，铁摄取过程中Fe - TF主要不被内化。结论是大鼠肝细胞质膜上存在TF受体，这些受体可能在细胞摄取过程中发挥作用，而TF分子不被内化。
