Cukor G, Solotorovsky M, Kuchler R J
J Bacteriol. 1973 Jul;115(1):277-83. doi: 10.1128/jb.115.1.277-283.1973.
Diphtheria toxin splits into two fragments when heated at 100 C for 10 min in a phosphate buffer. The separated fragments have molecular weights of 24,000 and 39,000, respectively. These molecular weights are similar to those of the A and B fragments found in diphtheria toxin preparations after thiol reduction. Since the separation of toxin into fragments is not complete, it is likely that only nicked toxin molecules having a cleaved peptide bond are split by heating. When toxin is suspended in phosphate buffer at pH 6.4, the B-like fragment precipitates, but at pH 7.8 it does not. Heated toxin is unable to intoxicate sensitive cells or cause a necrodermal response in animals. Fragment A produced by heating is active in inhibiting cell-free protein synthesis. It is able to intoxicate both HeLa and L cells when the uptake of the fragment is facilitated by addition of polyornithine to the cultures. Fragment B produced by heating is involved with binding to the cell surface. It is able to delay the action of toxin on KB cell cultures preincubated with fragment B.
在磷酸盐缓冲液中于100℃加热10分钟时，白喉毒素会裂解为两个片段。分离出的片段分子量分别为24,000和39,000。这些分子量与硫醇还原后白喉毒素制剂中发现的A和B片段的分子量相似。由于毒素裂解为片段并不完全，很可能只有具有断裂肽键的切口毒素分子会被加热裂解。当毒素悬浮于pH 6.4的磷酸盐缓冲液中时，类B片段会沉淀，但在pH 7.8时则不会。加热后的毒素无法使敏感细胞中毒，也不会在动物体内引起皮肤坏死反应。加热产生的A片段在抑制无细胞蛋白质合成方面具有活性。当向培养物中添加多聚鸟氨酸促进该片段的摄取时，它能够使HeLa细胞和L细胞中毒。加热产生的B片段参与与细胞表面的结合。它能够延迟毒素对预先用B片段孵育的KB细胞培养物的作用。
