Shih Y J, Baynes R D, Hudson B G, Flowers C H, Skikne B S, Cook J D
Department of Medicine, Kansas University Medical Center, Kansas City 66103.
J Biol Chem. 1990 Nov 5;265(31):19077-81.
Recent studies have provided immunological evidence for the existence of transferrin receptor in human serum and have revealed that its concentration is a sensitive measure of erythropoiesis and iron deficiency. The present study was undertaken to establish the molecular identity of this immunoreactive component. Purification from human serum was accomplished by immunoaffinity chromatography using, as the ligand, monoclonal antitransferrin receptor antibody. The receptor preparation contained two major components with Mr of 75,000 and 85,000, which were identified as transferrin and transferrin receptor, respectively. The physicochemical and immunochemical properties of the 85,000 serum receptor were compared with those established for intact placental transferrin receptor. The serum receptor exhibited an apparent Mr = 85,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under non-reducing conditions, as compared with 190,000 for placental transferrin receptor. Upon reduction, the Mr of serum receptor was unaltered, whereas, the 190,000 placental receptor dimer decreased to the expected monomer value of 95,000. Amino-terminal amino acid sequence analysis revealed that residues 1-19 of serum receptor were identical to residues 101-119 of intact receptor. These findings provide physicochemical evidence for the existence of transferrin receptor in human serum, establish its molecular identity as a truncated form lacking the cytoplasmic and transmembrane domains (residues 1-100) of intact receptor, and demonstrate that it exists as a transferrin-receptor complex in serum.
最近的研究为人类血清中转铁蛋白受体的存在提供了免疫学证据，并表明其浓度是红细胞生成和缺铁的敏感指标。本研究旨在确定这种免疫反应成分的分子身份。通过使用单克隆抗转铁蛋白受体抗体作为配体的免疫亲和层析从人血清中完成纯化。受体制剂包含两个主要成分，分子量分别为75,000和85,000，分别被鉴定为转铁蛋白和转铁蛋白受体。将85,000血清受体的物理化学和免疫化学性质与完整胎盘转铁蛋白受体的性质进行了比较。在非还原条件下，血清受体在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳上显示出明显的分子量为85,000，而胎盘转铁蛋白受体为190,000。还原后，血清受体的分子量不变，而190,000的胎盘受体二聚体降至预期的单体值95,000。氨基末端氨基酸序列分析表明，血清受体的第1-19位残基与完整受体的第101-119位残基相同。这些发现为人类血清中转铁蛋白受体的存在提供了物理化学证据，确定其分子身份为缺乏完整受体的细胞质和跨膜结构域（第1-100位残基）的截短形式，并证明它在血清中以转铁蛋白-受体复合物的形式存在。
