Awai M, Chipman B, Brown E B
J Lab Clin Med. 1975 May;85(5):785-96.
Iron atoms from the two iron-binding sites of transferrin in the maternal plasma were selectively transferred to fetal tissues across the placenta of the pregnant rat. Rat serum transferrin was selectively double-labeled with 55Fe bound to the A-site and 59Fe bound to the B-site and injected intravenously into pregnant rats at 11 to 20 days gestation. Ratios of 55Fe to 59Fe were measured in various maternal and fetal tissues sampled from 30 to 120 minutes after injection. In the maternal tissues preponderance of A-site 55Fe was observed in circulating red blood cells and in heme extracted from bone marrow and spleen; B-site 59Fe predominated in the liver parenchymal cells and proximal small intestine. As predicted by the Fletcher-Huehns hypothesis, placental transfer of radioiron resulted in a selective concentration of A-site 55Fe in all the fetal tissues including the fetal placenta, yolk sac, whole fetus, and in the separately analyzed liver heme and ferritin and in fetal blood. When the placenta was bypassed by direct injection of the selectively double-labeled transferrin into the umbilical vein, a reversal of the 55Fe/59Fe ratios of heme extracted from the fetal liver was observed. These studies confirm the concept of functional heterogeneity of iron atoms bound to transferrin and indicate that the placenta of rats between the eleventh and twentieth day of pregnancy selectively removes erythroblast-oriented iron from transferrin and diverts it to fetal tissues.
母体血浆中转铁蛋白两个铁结合位点的铁原子经孕鼠胎盘被选择性地转运至胎儿组织。将与A位点结合的55Fe和与B位点结合的59Fe选择性地对大鼠血清转铁蛋白进行双重标记，并在妊娠11至20天经静脉注射到孕鼠体内。在注射后30至120分钟采集的各种母体和胎儿组织中测量55Fe与59Fe的比率。在母体组织中，循环红细胞以及从骨髓和脾脏中提取的血红素中观察到A位点55Fe占优势；B位点59Fe在肝实质细胞和近端小肠中占主导。正如弗莱彻-许恩斯假说所预测的，放射性铁的胎盘转运导致A位点55Fe在所有胎儿组织中选择性富集，包括胎儿胎盘、卵黄囊、整个胎儿，以及单独分析的胎儿肝脏血红素、铁蛋白和胎儿血液中。当通过将选择性双重标记的转铁蛋白直接注入脐静脉来绕过胎盘时，观察到从胎儿肝脏中提取的血红素的55Fe/59Fe比率发生了逆转。这些研究证实了与转铁蛋白结合的铁原子功能异质性的概念，并表明妊娠第11至20天之间的大鼠胎盘会选择性地从转铁蛋白中去除定向于成红细胞的铁，并将其转移至胎儿组织。
