Hirst T R, Holmgren J
J Bacteriol. 1987 Mar;169(3):1037-45. doi: 10.1128/jb.169.3.1037-1045.1987.
Cholera toxin and heat-labile enterotoxin (LT) are structurally similar oligomeric proteins which are capable of being efficiently secreted from Vibrio cholerae. Here we report that these proteins transiently enter the periplasm of V. cholerae as they traverse the cell envelope to reach the extracellular milieu. Pulse-chase experiments on V. cholerae TRH7000 harboring an LT-encoding plasmid revealed that radiolabeled LT A and B subunits entered the periplasm rapidly, followed by their slow efflux (half-time, 13 min) into the medium. LT B-subunit efflux from the periplasm was calculated to be at a rate of ca. 170 monomers per min per cell (which is equivalent to 34 assembled LT holotoxin molecules per min per cell). These values were estimated to be sufficient to account for the increase in extracellular enterotoxin concentration during exponential cell growth. Thus, all enterotoxin subunits which are secreted into the medium can be assumed to be channelled via the periplasm. These findings led to an improved model of the pathway of toxin secretion by V. cholerae.
霍乱毒素和不耐热肠毒素（LT）是结构相似的寡聚蛋白，能够从霍乱弧菌中有效分泌。在此我们报告，这些蛋白在穿过细胞膜到达细胞外环境时会短暂进入霍乱弧菌的周质。对携带LT编码质粒的霍乱弧菌TRH7000进行脉冲追踪实验显示，放射性标记的LT A和B亚基迅速进入周质，随后缓慢流出（半衰期为13分钟）到培养基中。计算得出LT B亚基从周质流出的速率约为每分钟每个细胞170个单体（相当于每分钟每个细胞34个组装好的LT全毒素分子）。据估计，这些数值足以解释指数生长期细胞外肠毒素浓度的增加。因此，可以认为所有分泌到培养基中的肠毒素亚基都是通过周质运输的。这些发现促成了对霍乱弧菌毒素分泌途径的改进模型。
