Hisayasu S, Mugitani K, Orimo H, Ikeda Y, Satoh K, Hirai Y, Yoshino Y
Department of Biochemistry, Nippon Medical School, Tokyo, Japan.
Int J Hematol. 1991 Jun;54(3):201-8.
Transferrin (Tf) was found immunologically in pancreatic juice of normal rats at a concentration of 0.28 +/- 0.10 mg/ml but was found to be approximately 4-times higher in iron-deficient rats. Iron saturation of pancreatic Tf of normal rats was 40% and similar to that of serum Tf. Approximately 27% of a dose of iron from 59Fe-diferric Tf was absorbed through the ligated segments of proximal intestine in normal rats. The iron absorption ratio of 59Fe-diferric Tf was higher from the duodenal and jejunal segments than the ileum and significantly inhibited by monodansylcadaverine (MDC) or 20-times excess of unlabeled diferric Tf. The presence of Tf receptors was demonstrated by specific binding of 125I-diferric Tf to the brush border membrane vesicles of the small intestine in normal rats. The binding was not inhibited by the presence of albumin or IgG. The association constant (Ka) was 1.03 +/- 0.50 x 10(8) M-1 and number of binding sites was 5.10 +/- 0.96 x 10(12) sites/mg protein in the proximal intestine. The number of binding sites for Tf was higher in the proximal intestine than in the distal one. These results suggested that some iron was absorbed as diferric Tf into enterocytes through receptor-mediated endocytosis.
在正常大鼠的胰液中通过免疫学方法检测到转铁蛋白（Tf），其浓度为0.28±0.10毫克/毫升，但在缺铁大鼠中发现其浓度约高4倍。正常大鼠胰腺Tf的铁饱和度为40%，与血清Tf相似。在正常大鼠中，来自59Fe-双铁转铁蛋白的一剂铁约27%通过近端肠的结扎段被吸收。59Fe-双铁转铁蛋白在十二指肠和空肠段的铁吸收比率高于回肠，且被单丹磺酰尸胺（MDC）或20倍过量的未标记双铁转铁蛋白显著抑制。通过125I-双铁转铁蛋白与正常大鼠小肠刷状缘膜囊泡的特异性结合证明了Tf受体的存在。白蛋白或IgG的存在不会抑制这种结合。近端肠中的缔合常数（Ka）为1.03±0.50×10(8) M-1，结合位点数为5.10±0.96×10(12) 位点/毫克蛋白质。Tf的结合位点数在近端肠中高于远端肠。这些结果表明，一些铁作为双铁转铁蛋白通过受体介导的内吞作用被吸收进入肠细胞。
