Höffken B, Ködding R, Hesch R D
Clin Chim Acta. 1977 Jul 15;78(2):261-6. doi: 10.1016/0009-8981(77)90314-x.
The fate of T4 in target organs is conversion to T3 which is mainly responsible for the nuclear action of thyroid hormones. To further investigate this converting step the increase of T3 and its analogue rT3 in rat liver microsomes was measured by specific radioimmunoassays after adding T4 to the incubation medium. Maximal increase of T3 occurred at pH 6.0 and of rT3 at pH 9.5 indicating that two different enzymic systems may be involved in the deiodination of the tyrosyl or the phenolic ring of T4. An increase in the binding capacity of cytosol proteins for T4, T3 and rT3 with rising pH demonstrates that there is also a pH dependency of the cytoplasmic binding of these iodothyronines. These reaction conditions should not only be considered in in vitro experiments, but may also be of importance in modifying the availability of T3 for its nuclear receptors.
甲状腺激素在靶器官中的命运是转化为T3，T3主要负责甲状腺激素的核作用。为了进一步研究这一转化步骤，在孵育培养基中加入T4后，通过特异性放射免疫分析法测定大鼠肝微粒体中T3及其类似物反T3（rT3）的增加情况。T3在pH 6.0时达到最大增加，rT3在pH 9.5时达到最大增加，这表明T4酪氨酸基或酚环的脱碘可能涉及两种不同的酶系统。随着pH值升高，胞质溶胶蛋白对T4、T3和rT3的结合能力增加，这表明这些碘甲状腺原氨酸的细胞质结合也存在pH依赖性。这些反应条件不仅应在体外实验中予以考虑，而且对于改变T3对其核受体的可利用性可能也很重要。
