Amir S M, Kubota K, Tramontano D, Ingbar S H, Keutmann H T
Endocrinology. 1987 Jan;120(1):345-52. doi: 10.1210/endo-120-1-345.
TSH is a glycoprotein hormone whose carbohydrate content varies among different species. Although recent studies suggest that variants of TSH deficient in carbohydrate occur naturally, the significance of the carbohydrate moiety of TSH in respect to its thyrotropic function is unclear. The present studies were undertaken, therefore, to examine this question. A highly purified preparation of bovine TSH (bTSH) was deglycosylated by treatment with anhydrous hydrogen fluoride. Amino acid and carbohydrate analyses of the original and deglycosylated preparations indicated that approximately 85% of the carbohydrate originally present had been removed and that the protein moiety was unaltered. As judged from TSH radioreceptor assays, bTSH and deglycosylated bTSH (dg-bTSH) bound to human thyroid membranes with equal affinity, since both caused a half-maximal inhibition of [125I]bTSH binding at approximately equal concentrations. Nonetheless, dg-bTSH at optimal concentration displayed only about one third the activity of intact TSH in stimulating adenylate cyclase activity in human thyroid membranes. dg-bTSH also antagonized the adenylate cyclase-stimulating activity of intact bTSH in this system, but only weakly, since abolition of the bTSH effect required an approximately 40-fold higher concentration of dg-bTSH. In cultures of FRTL5 cells, a cloned line of follicular cells derived from normal rat thyroid, both intact and dg-bTSH enhanced cell growth, as measured by [3H]thymidine incorporation and stimulated cAMP release in the medium, but the response elicited by dg-bTSH was much less than that caused by equal concentrations of the intact hormone. In accord with the findings in the in vitro assays, dg-bTSH evoked a much smaller response than bTSH did in the in vivo mouse assay. It is concluded that although not required for receptor recognition, the carbohydrate moiety of bTSH is essential for the full expression of its biological activity.
促甲状腺激素（TSH）是一种糖蛋白激素，其碳水化合物含量在不同物种间有所差异。尽管最近的研究表明，缺乏碳水化合物的TSH变体可自然产生，但TSH的碳水化合物部分在其促甲状腺功能方面的意义尚不清楚。因此，开展了本研究以探讨这个问题。用无水氟化氢处理高度纯化的牛促甲状腺激素（bTSH）制剂使其去糖基化。对原始制剂和去糖基化制剂进行的氨基酸和碳水化合物分析表明，最初存在的碳水化合物约85%已被去除，且蛋白质部分未改变。从TSH放射受体分析判断，bTSH和去糖基化bTSH（dg-bTSH）与人甲状腺膜的结合亲和力相同，因为二者在大致相同浓度下均能使[125I]bTSH结合受到半数最大抑制。然而，最佳浓度的dg-bTSH在刺激人甲状腺膜中的腺苷酸环化酶活性时，其活性仅约为完整TSH的三分之一。在该系统中，dg-bTSH也拮抗完整bTSH的腺苷酸环化酶刺激活性，但作用较弱，因为要消除bTSH的作用，所需的dg-bTSH浓度要高约40倍。在FRTL5细胞培养物中（一种源自正常大鼠甲状腺的滤泡细胞克隆系），完整的和dg-bTSH均能促进细胞生长（通过[3H]胸腺嘧啶核苷掺入法测定）并刺激培养基中cAMP释放，但dg-bTSH引发的反应远小于相同浓度的完整激素所引起的反应。与体外试验结果一致，在体内小鼠试验中，dg-bTSH引发的反应比bTSH小得多。结论是，尽管bTSH的碳水化合物部分不是受体识别所必需的，但对其生物活性的充分表达至关重要。
