McDonel J L
Biochemistry. 1980 Oct 14;19(21):4801-7. doi: 10.1021/bi00562a014.
125I-Labeled enterotoxin from Clostridium perfringens was utilized to characterize the association of the enterotoxin with cells isolated from rabbit intestine and tissue homogenates from liver, kidney, and brain. The enterotoxin was found to bind in a specific and saturable manner to cells from intestine and to tissue homogenates from liver and kidney but not the brain. Detailed studies of the binding were carried out with the ileal epithelial intestinal cells. The rate and amount of binding of enterotoxin to cells appeared to be temperature dependent. Apparent affinity and association and dissociation rate constants were calculated for what appeared to be two classes of saturable binding sites. The amount of enterotoxin molecules that bound per milligram of cell protein was similar in tissue of intestinal, liver, and kidney origin (approximately 10(13) molecules/mg of cell protein). Spontaneous dissociation into the supernatant medium was observed to be much slower than expected from calculations based on the rate of association. Chaotropic ions did not enhance dissociation of the enterotoxin from cells. Enterotoxin binding was demonstrated to be heat labile (binding ability was lost after the enterotoxin was heated for 10 min at 60 degrees C). A mechanism is described whereby the enterotoxin binds and then is inserted into the membrane where it becomes trapped.
利用125I标记的产气荚膜梭菌肠毒素来表征该肠毒素与从兔肠道分离的细胞以及肝脏、肾脏和脑组织匀浆之间的关联。发现该肠毒素以特异性且可饱和的方式与肠道细胞以及肝脏和肾脏的组织匀浆结合，但不与脑组织结合。使用回肠上皮肠道细胞对结合进行了详细研究。肠毒素与细胞的结合速率和量似乎取决于温度。针对似乎两类可饱和结合位点计算了表观亲和力以及结合和解离速率常数。每毫克细胞蛋白结合的肠毒素分子数量在肠道、肝脏和肾脏来源的组织中相似（约10¹³个分子/毫克细胞蛋白）。观察到自发解离到上清培养基中的速度比基于结合速率的计算预期的要慢得多。离液离子不会增强肠毒素从细胞的解离。已证明肠毒素结合对热不稳定（肠毒素在60℃加热10分钟后结合能力丧失）。描述了一种机制，通过该机制肠毒素结合然后插入膜中并被困在其中。
