Van Obberghen E, Kasuga M, Hedo J A
Reprod Nutr Dev (1980). 1983;23(2 B):357-66. doi: 10.1051/rnd:19830305.
Using both biosynthetic and external labeling techniques, we have demonstrated that the insulin receptor consists of two major subunits with a molecular weight of approximately 135,000 and 95,000, respectively. These two major subunits are glycoproteins. Our data and observations from other laboratories have led to the suggestion that the insulin receptor is a heterodimer of the 134,000 and 95,000 subunits and, in fact, has an immunoglobulin-like structure with heavy and light chains held together by disulfide bonds. Biosynthetic studies showing the incorporation of all four labeled monosaccharides (fucose, mannose, galactose and glucosamine) into the two major subunits of the insulin receptor suggested that both subunits were likely to contain carbohydrate chains of the complex, N-linked type. External labeling techniques demonstrated that a portion of the protein and carbohydrate moiety of both subunits was exposed at the external cell surface. Further, labeling of the external oriented carbohydrates revealed remarkable differences in the nonreducing termini of the carbohydrate chains of both major subunits. Indeed, in the Mr 134,000 subunit, there appeared to be more exposed galactosyl or N-acetylgalactosaminyl (or both) residues, whereas the Mr 95,000 subunit seemed to have a higher degree of sialylation.
运用生物合成和外部标记技术，我们已证明胰岛素受体由两个主要亚基组成，其分子量分别约为135,000和95,000。这两个主要亚基均为糖蛋白。我们的数据以及其他实验室的观察结果表明，胰岛素受体是由134,000和95,000亚基组成的异二聚体，实际上具有免疫球蛋白样结构，其重链和轻链通过二硫键相连。生物合成研究表明，所有四种标记单糖（岩藻糖、甘露糖、半乳糖和葡糖胺）均掺入胰岛素受体的两个主要亚基中，这表明两个亚基可能都含有复杂的N-连接型碳水化合物链。外部标记技术表明，两个亚基的一部分蛋白质和碳水化合物部分暴露于细胞外表面。此外，对外部定向碳水化合物的标记显示，两个主要亚基碳水化合物链的非还原末端存在显著差异。实际上，在分子量为134,000的亚基中，似乎有更多暴露的半乳糖基或N-乙酰半乳糖胺基（或两者）残基，而分子量为95,000的亚基似乎具有更高程度的唾液酸化。
