SYNTHESIS OF THYROXINE TRANSPORT PROTEINS

人肝癌细胞（HepG 2）单层培养物先前已显示出， 合成并分泌甲状腺素结合球蛋白（TBG）。 本 利用这些细胞的研究表明，27 K蛋白，一种新的 在项目Z 01 AM 45000-18中描述的甲状腺素结合蛋白， 由肝脏产生。 令人信服的证据表明，TBG和27 K蛋白是 通过显示TBG mRNA和27 K mRNA可以在细胞内表达， 通过蔗糖梯度离心分离。 体外翻译 以（H3）甘露糖为前体的27 K mRNA和全细胞研究，或 （S35）在糖基化抑制剂存在下的甲硫氨酸， 衣霉素，证明27 K蛋白是非糖基化的， 似乎含有前肽 27 K蛋白分泌的动力学 与白蛋白相似，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，27 K蛋白是一个更突出的生物合成 比TBG在这些细胞中的产物。

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.