Gill D M, Clements J D, Robertson D C, Finkelstein R A
Infect Immun. 1981 Sep;33(3):677-82. doi: 10.1128/iai.33.3.677-682.1981.
The Escherichia coli heat-labile enterotoxin (LT) was found to have the same subunit structure as cholera toxin, namely, one A subunit and five B subunits. Reaction with a bisimidate generated all the possible cross-linked derivatives of A5B: B,2B ... 5B and A, AB ... A5B. The isolated B component, coligenoid, contained five B subunits and showed some tendency of polymerize: with a bisimidate it became covalently connected into the set B ... 5B with lesser amounts of 6B ... 10B, etc. The subunit formulas of two independently prepared samples of LT were both proved to be A5B by cross-linking, but their B pentamers migrated at different rates on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, indicating that they have different conformations. The faster (R) form could be converted to a diffuse slower (C) form by incubating it at 50 degrees C or at 37 degrees C with 0.2 M galactose, which is the terminal sugar of ganglioside GM1, the natural receptor for LT. Cholera toxin resembled the R form more than the C form of LT.
人们发现大肠杆菌不耐热肠毒素（LT）与霍乱毒素具有相同的亚基结构，即一个A亚基和五个B亚基。与双亚胺反应生成了A5B的所有可能的交联衍生物：B、2B……5B以及A、AB……A5B。分离得到的B组分，即类大肠杆菌素，含有五个B亚基，并表现出一定的聚合倾向：与双亚胺反应后，它共价连接形成B……5B，还有少量的6B……10B等。通过交联证明，两个独立制备的LT样品的亚基组成均为A5B，但在十二烷基硫酸钠存在下，它们的B五聚体在聚丙烯酰胺凝胶电泳中的迁移速率不同，这表明它们具有不同的构象。较快迁移的（R）型可以通过在50℃或37℃下与0.2M半乳糖（神经节苷脂GM1的末端糖，LT的天然受体）孵育而转化为扩散较慢的（C）型。霍乱毒素与LT的R型比C型更相似。
