Sugii S, Tsuji T
Department of Serology and Immunology, School of Medical Technology, Kitasato University, Kanagawa, Japan.
Biochim Biophys Acta. 1989 Jul 24;983(1):30-4. doi: 10.1016/0005-2736(89)90376-3.
To study the predominant binding substance for the heat-labile enterotoxin (LTc) isolated from chicken enterotoxigenic Escherichia coli, competitive binding assays were performed with neuraminidase-treated human type B erythrocytes and 125I-labeled B subunit of LTc (LTc-B). Of all inhibitors used, the ganglioside GM1 was the most effective in inhibiting the binding of 125I-labeled LTc-B to the erythrocytes. The other gangliosides used as inhibitors, gangliosides GD1b, GD1a, GM2, GT1b and GM3, were about 24, 166, 250, 440 and at least 440 times less reactive than ganglioside GM1, respectively. With glycoproteins as inhibitors, on the other hand, hog A + H, porcine thyroglobulin and bovine salivary mucin were over 10(4) times less potent. No inhibition was obtained by other mono-, di- and polysaccharides at the highest concentrations used. These findings suggest that the predominant binding substance on neuraminidase-treated human type B erythrocytes for the LTc-B is ganglioside GM1 and that the combining site of LTc-B may be specific for the terminal disaccharide (galactose-N-acetyl-D-galactosamine)-linked portion of ganglioside GM1.
为研究从鸡源产肠毒素大肠杆菌中分离出的不耐热肠毒素（LTc）的主要结合物质，我们用神经氨酸酶处理过的人B型红细胞和125I标记的LTc B亚基（LTc-B）进行了竞争性结合试验。在所有使用的抑制剂中，神经节苷脂GM1对抑制125I标记的LTc-B与红细胞的结合最为有效。用作抑制剂的其他神经节苷脂，即神经节苷脂GD1b、GD1a、GM2、GT1b和GM3，其反应活性分别比神经节苷脂GM1低约24、166、250、440倍和至少440倍。另一方面，以糖蛋白作为抑制剂时，猪A + H、猪甲状腺球蛋白和牛唾液粘蛋白的效力低10^4倍以上。在所用的最高浓度下，其他单糖、二糖和多糖均未产生抑制作用。这些发现表明，神经氨酸酶处理过的人B型红细胞上LTc-B的主要结合物质是神经节苷脂GM1，并且LTc-B的结合位点可能对神经节苷脂GM1的末端二糖（半乳糖-N-乙酰-D-半乳糖胺）连接部分具有特异性。
