The natural occurrence of insulin receptors in groups on adipocyte plasma membranes as demonstrated with monomeric ferritin-insulin.
The natural occurrence of insulin receptors in groups on adipocyte plasma membranes as demonstrated with monomeric ferritin-insulin.
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单体铁蛋白-胰岛素证实了脂肪细胞质膜上胰岛素受体的自然存在。
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发表时间：
1977
期刊：
影响因子：
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通讯作者：
R. Smith
中科院分区：
文献类型：
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作者：
L. Jarett;R. Smith
这项研究旨在证明所报道的胰岛素受体在脂肪细胞和分离的脂肪细胞质膜上随机分布的一小群受体位置上的分布是自然发生的现象还是人为的。可能的人工产物包括：(1)铁蛋白-胰岛素制剂中铁蛋白的低聚形式，(2)糖基在质膜上的不均匀分布，或(3)配体诱导的被占据的受体复合体的聚集。铁蛋白-胰岛素结合物的1.5M层析显示，铁蛋白-胰岛素复合体中的铁蛋白由55%的单体、15%的二聚体和30%的寡聚体组成。单体峰被提纯(>；95%)用于这些研究。阳离子铁蛋白是糖基化的标志，当与多聚甲醛固定的质膜孵育时，发现阳离子铁蛋白均匀分布在质膜上，表明糖基化反应是均匀分布的。用多价配体铁蛋白-刀豆蛋白A证明并抑制配体诱导的在离体质膜上聚集的能力。当与新鲜的膜在24°C孵育时，超过66%的铁蛋白-刀豆蛋白A受体以5个或更多的大簇形式存在，34%以单个或最多4个簇的形式存在。只有38%的铁蛋白-刀豆蛋白A受体以大簇的形式存在；62%的受体在孵育前用多聚甲醛预处理的膜上是单个或最多4簇。单体铁蛋白-胰岛素在脂肪细胞和纯化的脂肪细胞质膜上的分布相似，与早期关于铁蛋白-胰岛素的报道一致。在与刀豆蛋白A相似的培养条件下，研究了每毫升500μ单位的单体铁蛋白-胰岛素与分离质膜的结合。在所有三种条件下，新鲜的24℃和0-4℃的膜以及24℃的前置膜中，单体铁蛋白-胰岛素作为单个或2-6基团的分布模式是相同的，表明配体不会像刀豆蛋白A那样引起聚集成簇。胰岛素受体在小群体中的出现似乎是脂肪细胞质膜结构中的自然现象。
This study was designed to document whether the reported distribution of insulin receptors in small groups of receptor sites randomly distributed in the glycocalyx of adipocytes and isolated adipocyte plasma membranes was a naturally occurring phenomena or due to artifacts. Possible artifacts include: (1) oligomeric forms of ferritin in the ferritin-insulin preparation, (2) an uneven distribution of the glycocalyx on the plasma membrane, or (3) ligand-induced aggregation of occupied receptor complexes. Biogel A 1.5m chromatography of the ferritin-insulin conjugate revealed the ferritin in the ferritin-insulin complex to consist of 55% monomers, 15% dimers, and 30% oligomers. The monomer peak was purified (> 95%) for use in these studies. Cationic ferritin, a glycocalyx marker, when incubated with paraformaldehyde-fixed plasma membranes, was found to be uniformly distributed on the surface of the plasma membrane indicative of uniformly distributed glycocalyx. The ability to demonstrate and inhibit ligand-induced aggregation on the isolated plasma membrane was established with a multivalent ligand, ferritin-concanavalin A. More than 66% of the ferritin-concanavalin A receptors were found in large clusters of 5 or more and 34% as singletons or clusters of up to 4 when incubated at 24°C with fresh membranes. Only 38% of the ferritin-concanavalin A receptors were in large clusters; 62% were singletons or clusters up to 4 on membranes prefixed with paraformaldehyde before incubation. The distribution of the monomeric ferritin-insulin was similar on both adipocytes and purified adipocyte plasma membranes and was consistent with earlier reports with ferritin-insulin. The quantitative distribution of the monomeric ferritin-insulin as singletons or in groups of 2–6 was comparable between the intact cells and isolated membranes incubated at 24°C. The binding of 500 μUnits monomeric ferritin-insulin per ml to the isolated plasma membranes was studied under incubation conditions similar to those used with ferritin-concanavalin A. Under all three conditions, fresh membranes at 24°C and 0–4°C and prefixed membranes at 24°C, the pattern of distribution of the monomeric ferritin-insulin as singletons or groups of 2–6 was identical, indicating that the ligand was not causing aggregation into clusters as did the concanavalin A. Thus, the occurrence of insulin receptors in small groups appears to be a natural phenomenon in the plasma membrane structure of adipocytes.