Fukuda H, Greer M A
Acta Endocrinol (Copenh). 1975 Mar;78(3):468-80. doi: 10.1530/acta.0.0780468.
We have independently varied the degree of iodination and of iodothyronine formation over a wide range by acutely administering various doses of perchlorate and/or methimazole to severely iodine-deficient rats 30 min before giving 131-I- with graded quantities (1-100 mug of 127-I-). Thyroids were removed 4 h later and the soluble protein analyzed for labelled iodoamino acid composition and with sucrose density gradient ultracentrifugation. Since the total thyroid iodine content before administering 127I- was less than 1 mug, calculation of the degree of iodination and iodothyronine content of the labelled Tgb could be made from the known specificity of the injected labelled iodide. Newly organified iodine ranged from smaller than 0.1 to 1.4 mug/thyroid and labelled iodothyronines from smaller than 5 to 962 pmoles/thyroid. Both the degree of iodination and iodothyronine content varied directly with Tgb stability in the absence of inhibitors. But when Tgb iodination was kept constant, Tgb stability at pH 10.1 varied directly with iodothyronine content. When iodothyronine content was kept constant, Tgb stability was independent of the degree of iodination. Correlation of stability with iodothyronine content was highly significant (r=0.79, Psmaller than 0.001) but not of stability with iodine content (r=0.49, P larger than 0.05). We conclude that the primary determinant of Tgb stability in mild alkali is the iodothyronine content and not the degree of iodination of the protein. The increased Tgb stability may be induced by coupling between iodotyrosil residues of different 12 S subunits rather than between residues of the same 12 S subunit.
在给严重碘缺乏的大鼠急性给予不同剂量的高氯酸盐和/或甲巯咪唑30分钟后，再给予不同量（1 - 100μg的127 - I -）的131 - I，我们在很宽的范围内独立改变了碘化程度和碘甲状腺原氨酸的形成。4小时后取出甲状腺，对可溶性蛋白进行分析，以确定标记的碘氨基酸组成，并进行蔗糖密度梯度超速离心。由于在给予127I -之前甲状腺的总碘含量小于1μg，因此可以根据注射的标记碘化物的已知特异性来计算标记的甲状腺球蛋白的碘化程度和碘甲状腺原氨酸含量。新有机化的碘范围为小于0.1至1.4μg/甲状腺，标记的碘甲状腺原氨酸范围为小于5至962pmol/甲状腺。在没有抑制剂的情况下，碘化程度和碘甲状腺原氨酸含量均与甲状腺球蛋白稳定性直接相关。但是当甲状腺球蛋白碘化保持恒定时，pH 10.1条件下的甲状腺球蛋白稳定性与碘甲状腺原氨酸含量直接相关。当碘甲状腺原氨酸含量保持恒定时，甲状腺球蛋白稳定性与碘化程度无关。稳定性与碘甲状腺原氨酸含量的相关性非常显著（r = 0.79，P小于0.001），但与碘含量的相关性不显著（r = 0.49，P大于0.05）。我们得出结论，在弱碱中甲状腺球蛋白稳定性的主要决定因素是碘甲状腺原氨酸含量，而不是蛋白质的碘化程度。甲状腺球蛋白稳定性的增加可能是由不同12S亚基的碘酪氨酸残基之间的偶联诱导的，而不是同一12S亚基残基之间的偶联。
