Lai C Y, Mendez E, Chang D
J Infect Dis. 1976 Mar;133 Suppl:23-30. doi: 10.1093/infdis/133.supplement_1.s23.
The toxin of Vibrio cholerae was separated into two subunits by gel filtration on Sephadex G-75 in 5% formic acid. The subunits were designated A and B. Amino acid analysis indicated that subunit B corresponded to choleragenoid. Renatured subunit B was found to be antigenically identical to the whole molecule, whereas renatured subunit A was not. On reduction and S-carboxymethylation with [2-14C] iodoacetate in 8 m urea, subunit A separated into two polypeptides of unequal sizes, A1 and A2, with equal amounts of radioactivity. Subunit B, on the other hand, remained a single molecular species. Molecular weights of the polypeptides A1, A2, and B were estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate-urea buffer, in conjunction with amino acid analysis, to be 20,000, 7,500, and 9,500 daltons, respectively. The carboxyl terminal sequence of subunit B was found to be -Met-Ala-Asn. After treatment of toxin with cyanogen bromide, the peptide Ala-Asn could be isolated and quantitated. From this data the number of B polypeptides in a molecule of toxin was estimated as six.
霍乱弧菌毒素在5%甲酸中经Sephadex G - 75凝胶过滤分离为两个亚基。这两个亚基分别命名为A和B。氨基酸分析表明亚基B与类霍乱原相对应。发现复性后的亚基B在抗原性上与整个分子相同，而复性后的亚基A则不同。在8m尿素中用[2 - 14C]碘乙酸进行还原和S - 羧甲基化后，亚基A分离为两条大小不等的多肽链A1和A2，它们的放射性相同。另一方面，亚基B仍为单一分子形式。通过在十二烷基硫酸钠 - 尿素缓冲液中进行聚丙烯酰胺凝胶电泳并结合氨基酸分析，估计多肽链A1、A2和B的分子量分别为20,000、7,500和9,500道尔顿。发现亚基B的羧基末端序列为 - Met - Ala - Asn。用溴化氰处理毒素后，可分离并定量肽段Ala - Asn。根据这些数据，估计毒素分子中B多肽链的数量为6条。
