Benvenga S, Cahnmann H, Gregg R, Robbins J
Clinical Endocrinology Branch, NIDDK, Bethesda, MD 20892.
Biochimie. 1989 Feb;71(2):263-8. doi: 10.1016/0300-9084(89)90063-1.
Human plasma low density lipoprotein (LDL), which binds 0.2% of plasma T4, was shown to interact with the hormone through its protein moiety, apolipoprotein B-100. LDL and LDL2, the major subfraction of LDL, were found to have 3 equivalent binding sites for T4 with Ka = 2.5 x 10(6) M-1. Photoaffinity labeling of LDL with inner ring-labeled [125I]T4, followed by SDS-PAGE or agarose-SDS-PAGE of the labeled products, revealed that apoB-100 and its proteolytic cleavage products, apoB-74 and apoB-26, bound [125I]T4. In the presence of 1 or 10 microM T4, labeling was decreased in 7 separate experiments by 40-53% or 65-86%, respectively, consistent with a Ka of approximately 10(6) M-1. Binding of T4 to apoB-100 associated with VLDL was also demonstrated by photoaffinity labeling. The observed thyroid hormone binding property of lipid-complexed apoB-100 and the knowledge that receptors for the apolipoprotein exist in various tissues suggest a possible physiological role in thyroid hormone transport.
人血浆低密度脂蛋白（LDL）可结合0.2%的血浆甲状腺素（T4），研究表明它通过其蛋白质部分载脂蛋白B - 100与该激素相互作用。LDL及其主要亚组分LDL2被发现具有3个与T4的等效结合位点，解离常数（Ka） = 2.5×10⁶ M⁻¹。用内环标记的[¹²⁵I]T4对LDL进行光亲和标记，然后对标记产物进行十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS - PAGE）或琼脂糖 - SDS - PAGE分析，结果显示载脂蛋白B - 100及其蛋白水解产物载脂蛋白B - 74和载脂蛋白B - 26可结合[¹²⁵I]T4。在1或10微摩尔/升T4存在的情况下，在7个独立实验中标记分别减少了40% - 53%或65% - 86%，这与大约10⁶ M⁻¹的解离常数一致。光亲和标记也证明了T4与极低密度脂蛋白（VLDL）相关的载脂蛋白B - 100的结合。脂质复合的载脂蛋白B - 100所观察到的甲状腺激素结合特性以及已知该载脂蛋白在各种组织中存在受体，提示其在甲状腺激素运输中可能具有生理作用。
