Bacha P, Murphy J R, Reichlin S
Endocrinology. 1983 Sep;113(3):1072-6. doi: 10.1210/endo-113-3-1072.
We have previously demonstrated that a hybrid protein consisting of TRH linked to CRM45, a fragment of diphtheria toxin which lacks its native cell-binding moiety, specifically binds to TRH receptors in vitro. In this study we have examined its in vivo binding and shown that after iv injection, this complex labeled with 125I is selectively concentrated in the normal anterior pituitary and that concomitant administration of cold TRH reduces its uptake. Displaceable uptake was also demonstrated in the hypothalamus and testis, whereas nondisplaceable binding exceeding that of CRM45 alone was shown in the ovary and the breast parenchyma of lactating rats. Similar experiments with tritiated TRH were performed. We found that although there was uptake of the material by many tissues, almost all of the radioactivity was in the form of TRH degradation products. Therefore, we conclude that TRH linked to a large carrier like CRM45 may be a more revealing indicator of in vivo binding affinities than native TRH.
我们之前已经证明，一种由促甲状腺激素释放激素（TRH）与CRM45连接而成的杂合蛋白能在体外特异性结合TRH受体，其中CRM45是白喉毒素的一个片段，缺乏其天然的细胞结合部分。在本研究中，我们检测了它在体内的结合情况，结果显示静脉注射后，这种用125I标记的复合物选择性地浓集于正常垂体前叶，同时给予冷TRH会减少其摄取。在下丘脑和睾丸中也显示出可置换摄取，而在卵巢和哺乳期大鼠的乳腺实质中显示出不可置换结合，且超过单独CRM45的结合。我们用氚标记的TRH进行了类似实验。我们发现，尽管许多组织都摄取了该物质，但几乎所有放射性都以TRH降解产物的形式存在。因此，我们得出结论，与像CRM45这样的大载体连接的TRH可能比天然TRH更能揭示体内结合亲和力。
