Sviridov O V
Biokhimiia. 1994 May;59(5):625-38.
The thyroid hormones--thyroxine (T4) and triiodothyronine (T3)--are capable of associating with human plasma high (HDL), low (LDL) and very low density lipoprotein particles (VLDL). Apolipoproteins (apo) act as the hormone-binding components of the lipoprotein particles. The thyroid hormone binding to apolipoproteins is a time-dependent, reversible, saturable and sensitive to specific inhibitors interaction with the structurally isolated site in the protein which is complementary to the ligand. The number of such sites per macromolecule varies from one (apoA-I) to three (apoB-100). Low affinities (Ka approximately 10(5)-10(6) M-1) for T4 are characteristic of apoA-II, apoA-IV, apoE and apoB-100, while apoA-I and its lipid complex, apoA-I-HDL display sufficiently high affinities for the hormone (Ka approximately 10(7)-10(8) M-1). The active site of apoA-I-HDL contains a chemical group interacting with the ionized phenolic ring hydroxy-group of T4, includes cavities capable of accommodating iodine atoms of the ligand molecule, has a hydrophobic nature and low stereospecificity and is located close to the surface of the protein globule in the N-terminal part of polypeptide chain conformationally associated with the polar surface monolayer of the lipid matrix. Three hormone-binding sites in apoB-100 are located in different regions of the polypeptide chain which are distant from each other and lie outside the sites of heparin and cellular LDL receptor binding. ApoB-100 and apoE stimulate T4 entry into fibroblasts, while apoA-I inhibits the interaction of T4 and T3 with human placental plasma membranes.
甲状腺激素——甲状腺素（T4）和三碘甲状腺原氨酸（T3）——能够与人类血浆中的高密度脂蛋白（HDL）、低密度脂蛋白（LDL）和极低密度脂蛋白颗粒（VLDL）相结合。载脂蛋白（apo）作为脂蛋白颗粒的激素结合成分。甲状腺激素与载脂蛋白的结合是一个时间依赖性、可逆、可饱和且对特定抑制剂敏感的过程，该过程涉及与蛋白质中与配体互补的结构孤立位点相互作用。每个大分子中此类位点的数量从一个（apoA-I）到三个（apoB-100）不等。apoA-II、apoA-IV、apoE和apoB-100对T4的亲和力较低（Ka约为10⁵ - 10⁶ M⁻¹），而apoA-I及其脂质复合物apoA-I-HDL对该激素具有足够高的亲和力（Ka约为10⁷ - 10⁸ M⁻¹）。apoA-I-HDL的活性位点包含一个与T4的离子化酚环羟基相互作用的化学基团，有能够容纳配体分子碘原子的腔，具有疏水性和低立体特异性，并且位于多肽链N端部分的蛋白质球表面附近，该部分与脂质基质的极性表面单层构象相关。apoB-100中的三个激素结合位点位于多肽链彼此相距较远的不同区域，且位于肝素和细胞LDL受体结合位点之外。apoB-100和apoE刺激T4进入成纤维细胞，而apoA-I抑制T4和T3与人胎盘质膜的相互作用。
