Chin W W, Habener J F
Endocrinology. 1981 May;108(5):1628-33. doi: 10.1210/endo-108-5-1628.
Glycosylation of newly synthesized subunits of TSH, a regulator of thyroid hormone synthesis and secretion, was studied in a mouse pituitary thyrotropic tumor in vitro. Subunits were pulse labeled by incubations of the tumor for 10 or 30 min with [35S]methionine, followed by chase incubations with unlabeled methionine for 30--90 min. The sensitivity of the subunit oligosaccharides to cleavage by the glycosidase endo-beta-N-acetylglucosaminidase H (Endo H) was determined by comparisons of the electrophoretic mobilities, on sodium dodecyl sulfate-polyacrylamide gels, of Endo H-treated and untreated labeled subunits in cells and media. We found that oligosaccharides of most of the intracellular subunits remained sensitive, whereas the oligosaccharides of all subunits released from the tumor were resistant to cleavage by Endo H during the transport of the subunits within the secretory pathway. Therefore, alterations in the carbohydrate structure of the subunits occur close to the time of secretion of the subunits and presumably represent late distal glycosylation steps that convert the oligosaccharides from high mannose to complex types. Late glycosylation may serve extraglandular functions, such as enhanced metabolic stability or expression of recognition sites for interaction with target organ receptors.
促甲状腺激素（TSH）是甲状腺激素合成与分泌的调节因子，我们对其新合成亚基的糖基化进行了体外小鼠垂体促甲状腺瘤研究。将肿瘤与[35S]甲硫氨酸孵育10或30分钟对亚基进行脉冲标记，随后用未标记的甲硫氨酸进行30 - 90分钟的追踪孵育。通过比较细胞和培养基中经内切β - N - 乙酰葡糖胺糖苷酶H（Endo H）处理和未处理的标记亚基在十二烷基硫酸钠 - 聚丙烯酰胺凝胶上的电泳迁移率，来确定亚基寡糖对Endo H切割的敏感性。我们发现，大多数细胞内亚基的寡糖仍然敏感，而在分泌途径中运输时，肿瘤释放的所有亚基的寡糖都对Endo H的切割具有抗性。因此，亚基碳水化合物结构的改变发生在亚基分泌的时间附近，推测代表寡糖从高甘露糖型转变为复杂型的晚期远端糖基化步骤。晚期糖基化可能具有腺体外功能，如增强代谢稳定性或表达与靶器官受体相互作用的识别位点。
