Waldbillig R J, Arnold D R, Fletcher R T, Chader G J
Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892.
Invest Ophthalmol Vis Sci. 1990 Jun;31(6):1015-22.
The sclera of embryonic (days 10 and 14) and young adult (2-week posthatching chicks) contains distinct binding sites for insulin and for insulin-like growth factor-1 (IGF-1). Since there is a nearly 50% decrease in insulin and IGF-1 binding between embryonic day 10 and the 2nd week posthatching, it is clear that these sites are developmentally regulated. The affinity of each binding site for its ligand is stable across development. This suggests that the developmental decrease in binding is the result of a decrease in the number of binding sites. The insulin binding site in the sclera is specific for insulin since it has a high affinity for insulin and a lower affinity for IGF-1 (IC50 for unlabeled insulin = 0.4 nM; unlabeled IGF-1 = 5.0 nM). The embryonic chick sclera also contains two high-affinity IGF-1 binding sites. One of these sites exhibits poor binding specificity since it has an equal affinity for insulin and IGF-1. However, the specificity of this site increases in the young adult. The second IGF-1 binding site exhibits a more conventional specificity in that it has a higher affinity for IGF-1 than for insulin. The specificity of this binding site also improves in the young adult. The presence of insulin and IGF-1 receptor binding site subtypes is not correlated with structurally different receptor binding subunits since only a single population of binding subunits is observed (apparent molecular weight of 125 +/- 2.7 kD) in embryonic and adult sclera.(ABSTRACT TRUNCATED AT 250 WORDS)
胚胎期（第10天和第14天）及年轻成年期（孵化后2周的雏鸡）的巩膜含有胰岛素及胰岛素样生长因子-1（IGF-1）的独特结合位点。由于胚胎期第10天到孵化后第2周之间胰岛素和IGF-1结合力下降了近50%，显然这些位点受发育调控。每个结合位点对其配体的亲和力在整个发育过程中保持稳定。这表明结合力的发育性下降是结合位点数减少的结果。巩膜中的胰岛素结合位点对胰岛素具有特异性，因为它对胰岛素亲和力高，对IGF-1亲和力低（未标记胰岛素的IC50 = 0.4 nM；未标记IGF-1 = 5.0 nM）。胚胎期雏鸡巩膜还含有两个高亲和力IGF-1结合位点。其中一个位点结合特异性较差，因为它对胰岛素和IGF-1的亲和力相同。然而，该位点的特异性在年轻成年期有所增加。第二个IGF-1结合位点表现出更传统的特异性，即它对IGF-1的亲和力高于对胰岛素的亲和力。该结合位点的特异性在年轻成年期也有所改善。胰岛素和IGF-1受体结合位点亚型的存在与结构不同的受体结合亚基无关，因为在胚胎期和成年期巩膜中仅观察到单一群体的结合亚基（表观分子量为125 +/- 2.7 kD）。（摘要截断于250字）
