SYNTHESIS OF THYROXINE TRANSPORT PROTEINS

人肝癌细胞(HepG2)单层培养先前已被证明 合成和分泌甲状腺激素结合球蛋白(TBG)。现在 研究使用这些细胞来证明27K蛋白，一种新的 项目Z01 AM 45000-18中描述的甲状腺激素结合蛋白也是 由肝脏产生。令人信服的证据表明，TBG和27K蛋白是 结果表明，TbG基因和27K基因可以表达不同的蛋白质。 用蔗糖梯度离心法分离。阿司匹林的体外翻译 27K信使核糖核酸和以(H3)甘露糖为前体的全细胞研究，或 (S35)在糖基化抑制剂存在的情况下的蛋氨酸， 衣霉素，证明了27K蛋白是非糖基化的 似乎含有一种前肽。27K蛋白分泌动力学的研究 与白蛋白相似，但比TBG快，反映了其 非糖蛋白性质。猴肝癌细胞的早期研究 培养表明，27K蛋白是一种更突出的生物合成 在这些细胞中的产物比TBG更好。

Human hepatoma cell (HepG2) monolayer cultures has previously been shown to synthesize and secrete thyroxine-binding globulin (TBG). The present studies employed these cells to demonstrate that 27 K protein, a novel thyroxine-binding protein described in Project Z01 AM 45000-18, is also produced by the liver. Convincing evidence that TBG and 27 K protein are distinct proteins was obtained by showing that TBG mRNA and 27 K mRNA can be separated by sucrose gradient centrifugation. In vitro translation of 27 K mRNA and whole cell studies with (H3)mannose as precursor, or (S35)methionine in the presence of the glycosylation inhibitor, tunicamycin, proved that 27 K protein is nonglycosylated and does not appear to contain a pro-peptide. The kinetics of 27 K protein secretion was similar to that of albumin and faster than that of TBG, reflecting its non-glycoprotein nature. Earlier studies with monkey hepatoma cell cultures showed that 27 K protein was a much more prominent biosynthetic product than TBG in these cells.