組織の甲状線ホルモン結合蛋白に関する研究:第3篇 甲状腺ホルモンとラット血清および肝可溶性蛋白との結合並びに肝の甲状腺ホルモン結合蛋白に関するSephadex Gel濾過による研究
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Previous reports provided the confirmatory evidences for the existence of both cellular thyroxine-binding protein (C-T<SUB>4</SUB>BP) and cellular triiodothyronine-binding protein (C-T<SUB>3</SUB> BP) in rat liver. The present paper describes further investigation concerning C-T<SUB>4</SUB>BP and C-T<SUB>3</SUB>BP by gel filtration on Sephadex G-25 and G-100. The polysaccharide matrix of Sephadex is known to adsorb phenolic compounds such as the thyroid hormones. It would be possible to take advantage of this phenomenon in order to eliminate the thyroid hormones bound nonspecifically to the cellular proteins and, further, to compare the affinity of the hormones for various proteins.<BR>Rat liver soluble proteins containing <SUP>131</SUP>I-labeled L-thyroxine (T<SUB>4</SUB>-<SUP>131</SUP>I) and L-triiodothyronine (T<SUB>3</SUB>_<SUP>131</SUP>I) were filtered through a Sephadex G-25 column and fractionated with ammonium sulfate. <SUP>131</SUP>I-labeled hormones bound loosely to liver proteins were eliminated by adsorption to Sephadex gel, and this has clarified the existence of C-T<SUB>4</SUB>BP and C-T<SUB>3</SUB>BP which bound the hormones more tightly. Both the C-T<SUB>4</SUB>BP and the C-T<SUB>3</SUB>BP were found to be precipitated between 0 and 30% saturation of ammonium sulfate.<BR>Rat serum and liver soluble proteins containing T<SUB>4</SUB>-<SUP>131</SUP>I and T<SUB>3</SUB>-<SUP>131</SUP>I were fractionated by gel filtration on Sephadex G-100. Both the C-T<SUB>4</SUB>BP and the C-T<SUB>3</SUB>BP were found to exist in the protein fraction non-diffusible into the gel grains, whereas serum T<SUB>4</SUB>BP emerged in the tailing position of the protein peak corresponding to albumin. These studies indicate the availability for separation of C-T<SUB>4</SUB>BP and C-T<SUB>3</SUB>BP from serum T<SUB>4</SUB>BP and other proteins. This finding also supported the previous suggestion that rat serum T<SUB>4</SUB>BP might not exactly correspond to albumin, and indicated that its molecular size might be a little smaller than that of albumin.<BR>The relative affinities of the thyroid hormones for serum and liver soluble proteins were compared by the use of Sephadex. The affinity of T<SUB>3</SUB> for serum was much lower than that of T<SUB>4</SUB>whereas the affinity of T<SUB>3</SUB> for liver soluble proteins was almost equal to that of T<SUB>4</SUB>. This may be due, in part, to the more rapid cellular penetration of T<SUB>3</SUB> compared to T<SUB>4</SUB>.
- 一般社団法人 日本内分泌学会の論文
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