Wilkins J R, D'Ercole A J
J Clin Invest. 1985 Apr;75(4):1350-8. doi: 10.1172/JCI111836.
By using disuccinimidyl suberate, we have covalently cross-linked 125I-labeled somatomedin-C (Sm-C)/insulinlike growth factor I to specific binding proteins in human plasma. In unfractionated plasma samples from normal and acromegalic donors, 125I-Sm-C binding-protein complexes with relative molecular weights (Mr) of 160,000, 135,000, 110,000, 80,000, 50,000, 43,000-35,000, and 28,000-24,000 were consistently observed. In contrast, the 43,000-35,000-mol wt species were frequently the only specific complexes observed in hypopituitary plasma and were consistently more intensely labeled in such samples. Reduction of samples with beta-mercaptoethanol did not alter the electrophoretic pattern of these 125I-Sm-C binding-protein complexes. All Sm-C binding proteins, with the exception of the 43,000-35,000-mol wt complex, were adsorbed by concanavalin A-Sepharose. When acromegalic or normal plasma was fractionated on a Sephadex G-200 column and affinity labeled, the same complexes that were adsorbed by concanavalin A were found in fractions that eluted near the gamma-globulin peak. On the other hand, the 43,000-35,000-mol wt complex consistently eluted in size-appropriate fractions near the albumin peak. These data suggest that the growth hormone (GH)-dependent Sm-C binding protein, represented by the 160,000-mol wt complex, is in some way composed of smaller species, i.e., the 135,000-, 110,000-, 80,000-, 50,000-, and 28,000-24,000-mol wt complexes. Acid incubation of plasma prior to Sephadex G-200 chromatography results in the elimination of specific 125I-Sm-C binding-protein complexes which elute near gamma-globulin and a concurrent increase in the labeling intensity of the 28,000-24,000-mol wt complexes. We speculate, therefore, that each of the GH-dependent Sm-C binding-protein complexes represents an oligomer composed of 28,000-24,000-mol wt protomers. The 43,000-35,000-mol wt species is not dependent upon GH and appears to represent a different type of Sm-C binding protein.
通过使用辛二酸双琥珀酰亚胺酯，我们已将125I标记的生长调节素-C（Sm-C）/胰岛素样生长因子I与人类血浆中的特异性结合蛋白共价交联。在来自正常和肢端肥大症供体的未分级血浆样本中，始终观察到相对分子质量（Mr）为160,000、135,000、110,000、80,000、50,000、43,000 - 35,000和28,000 - 24,000的125I - Sm-C结合蛋白复合物。相比之下，43,000 - 35,000分子量的复合物在垂体功能减退血浆中常常是唯一观察到的特异性复合物，并且在这类样本中其标记强度始终更高。用β-巯基乙醇还原样本并未改变这些125I - Sm-C结合蛋白复合物的电泳图谱。除了43,000 - 35,000分子量的复合物外，所有Sm-C结合蛋白都被伴刀豆球蛋白A - 琼脂糖吸附。当将肢端肥大症或正常血浆在葡聚糖G - 200柱上分级分离并进行亲和标记时，在γ-球蛋白峰附近洗脱的级分中发现了被伴刀豆球蛋白A吸附的相同复合物。另一方面，43,000 - 35,000分子量的复合物始终在白蛋白峰附近大小合适的级分中洗脱。这些数据表明，以160,000分子量复合物为代表的生长激素（GH）依赖性Sm-C结合蛋白在某种程度上由较小的物种组成，即135,000 -、110,000 -、80,000 -、50,000 -和28,000 - 24,000分子量的复合物。在葡聚糖G - 200色谱之前对血浆进行酸孵育会导致在γ-球蛋白附近洗脱的特异性125I - Sm-C结合蛋白复合物消失，同时28,000 - 24,000分子量复合物的标记强度增加。因此，我们推测每个GH依赖性Sm-C结合蛋白复合物代表一个由28,000 - 24,000分子量原体组成的寡聚物。43,000 - 35,000分子量的物种不依赖于GH，似乎代表一种不同类型的Sm-C结合蛋白。
