Finkelstein R A, LaRue M K, LoSpalluto J J
Infect Immun. 1972 Dec;6(6):934-44. doi: 10.1128/iai.6.6.934-944.1972.
Initial studies, by using polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), led to the attractive hypothesis that the cholera exo-enterotoxin (choleragen) consisted of two noncovalently linked peptides of 56,000 and 28,000 molecular weight. The spontaneous toxoid (choleragenoid) appeared to be identical with the 56,000 molecular weight piece. The results appeared to be very similar to those obtained recently with diphtheria toxin. However, they did not agree with earlier studies which indicated that both the toxin and the toxoid consisted of subunits of approximately 14,000 molecular weight. More extensive investigation, by using gel filtration with (3)H-labeled toxin, ultracentrifugation, and immunologic studies, failed to support the observations of SDS-gel electrophoresis, suggesting the existence of a 28,000 molecular weight fragment which is unique to the toxin. The results were more compatible with our earlier observations regarding subunit composition. It is concluded that these proteins are relatively resistant to dissociation by SDS and need to be unfolded by prior treatment for more complete dissociation into subunits. Indirect evidence suggests that the 28,000 fragment may be a dimer, or larger aggregate, of a smaller subunit which can be integrated in the formation of choleragenoid. It is also evident that caution should be exercised in the interpretation of results, however pleasing, obtained only by SDS-gel electrophoresis.
最初的研究是在十二烷基硫酸钠（SDS）存在的情况下使用聚丙烯酰胺凝胶电泳进行的，由此得出了一个引人注目的假设，即霍乱外肠毒素（霍乱毒素）由两种非共价连接的肽组成，分子量分别为56,000和28,000。自发类毒素（类霍乱毒素）似乎与分子量为56,000的片段相同。这些结果似乎与最近对白喉毒素的研究结果非常相似。然而，它们与早期的研究结果不一致，早期研究表明毒素和类毒素都由分子量约为14,000的亚基组成。通过使用用（3）H标记的毒素进行凝胶过滤、超速离心和免疫学研究进行的更广泛调查，未能支持SDS凝胶电泳的观察结果，表明存在一种毒素特有的分子量为28,000的片段。这些结果与我们早期关于亚基组成的观察结果更相符。得出的结论是，这些蛋白质对SDS解离具有相对抗性，需要通过事先处理使其展开，以便更完全地解离成亚基。间接证据表明，28,000片段可能是较小亚基的二聚体或更大的聚集体，它可以整合到类霍乱毒素的形成中。同样明显的是，在解释仅通过SDS凝胶电泳获得的结果时，无论结果多么令人满意，都应谨慎行事。
