Kallincos N C, Wallace J C, Francis G L, Ballard F J
Department of Biochemistry, University of Adelaide, Australia.
J Endocrinol. 1990 Jan;124(1):89-97. doi: 10.1677/joe.0.1240089.
Chicken insulin-like growth factor-II (cIGF-II) has been characterized by amino acid sequencing, by its receptor and binding protein interactions and by its biological activities in cultured cells in order to help define the significance of the peptide in the growth process. Chicken IGF-II has an N-terminal region and several amino acid substitutions in the mid-peptide region that differ from the mammalian growth factor. Nevertheless, cIGF-II was indistinguishable from ovine IGF-II in all assay systems, including those involving chicken receptors and chicken binding proteins. Thus the amino acid substitutions did not modify the biological activities. In chick embryo fibroblasts, labelled bovine IGF-II or cIGF-II bound to a receptor with size and specificity properties expected for a type 1 IGF receptor, except that IGF-I competition for binding was less than IGF-II competition. No evidence for a type 2 receptor was obtained. The relatively lower biological activity of IGF-I compared with IGF-II in chick embryo fibroblasts contrasts with the much higher potency of IGF-I in rat L6 myoblasts. This difference can be explained by a combination of an inhibitory, IGF-II-specific binding protein produced only by the rat cells as well as the unusual receptor specificity of the chicken cells.
鸡胰岛素样生长因子-II（cIGF-II）已通过氨基酸测序、其与受体和结合蛋白的相互作用以及在培养细胞中的生物学活性进行了表征，以帮助确定该肽在生长过程中的重要性。鸡IGF-II具有一个N端区域，并且在肽中间区域有几个氨基酸取代，这与哺乳动物生长因子不同。然而，在所有检测系统中，包括涉及鸡受体和鸡结合蛋白的系统，cIGF-II与绵羊IGF-II没有区别。因此，氨基酸取代并未改变生物学活性。在鸡胚成纤维细胞中，标记的牛IGF-II或cIGF-II与1型IGF受体预期的大小和特异性特性的受体结合，只是IGF-I对结合的竞争小于IGF-II竞争。未获得2型受体的证据。与IGF-II相比，IGF-I在鸡胚成纤维细胞中的生物学活性相对较低，这与IGF-I在大鼠L6成肌细胞中的高效能形成对比。这种差异可以通过仅由大鼠细胞产生的一种抑制性、IGF-II特异性结合蛋白以及鸡细胞不寻常的受体特异性共同作用来解释。
