Goetze A, Kanellopoulos J, Rice D, Metzger H
Biochemistry. 1981 Oct 27;20(22):6341-9. doi: 10.1021/bi00525a009.
The high-affinity membrane receptor for immunoglobulin E on mast cells and on a tumor analogue, rat basophilic leukemia cells, consists of two polypeptide chains: an alpha chain of Mr congruent to 50,000 and a beta chain of Mr congruent to 30,000. In this study we reacted alpha chains purified from tumor cells with proteolytic and glycolytic enzymes and compared the products by using differential labeling procedures. A variety of proteolytic enzymes cleave the chain into two similar-sized fragments, alpha 1 and alpha 2. The alpha 1 fragment behaves as if it were slightly larger on electrophoresis through polyacrylamide gels and is rich in carbohydrate as determined by incorporation of [14C]glucosamine. Less incorporation is observed into alpha 2 but it, like alpha 1, binds to concanavalin A. Labeling of the surface proteins on intact cells by lactoperoxidase-catalyzed iodination leads to preferential, perhaps exclusive, labeling of the alpha 2 fragment. The relative proportion of incorporated 3H-labeled amino acids and radioactive Bolton--Hunter reagent suggests that the polypeptide portions of alpha 1 and alpha 2 are similar in size. From these and other data we propose that the alpha chain may be U-shaped. Results from endoglycosidase digestions show that the receptor as isolated is heterogeneous because of variable glycosylation.
肥大细胞以及一种肿瘤类似物——大鼠嗜碱性白血病细胞上的免疫球蛋白E高亲和力膜受体，由两条多肽链组成：一条分子量约为50,000的α链和一条分子量约为30,000的β链。在本研究中，我们使从肿瘤细胞中纯化得到的α链与蛋白水解酶和糖酵解酶反应，并通过差异标记程序比较产物。多种蛋白水解酶将该链切割成两个大小相似的片段，α1和α2。α1片段在通过聚丙烯酰胺凝胶电泳时表现得似乎稍大一些，并且通过[14C]葡糖胺掺入法测定富含碳水化合物。α2中观察到的掺入较少，但它与α1一样，能与伴刀豆球蛋白A结合。通过乳过氧化物酶催化碘化对完整细胞表面蛋白进行标记，导致α2片段优先（可能是唯一）被标记。掺入的3H标记氨基酸和放射性博尔顿-亨特试剂的相对比例表明，α1和α2的多肽部分大小相似。根据这些及其他数据，我们推测α链可能呈U形。内切糖苷酶消化的结果表明，分离得到的受体由于糖基化可变而具有异质性。
