Hudson T H, Scharff J, Kimak M A, Neville D M
Laboratory of Molecular Biology, National Institute of Mental Health, Bethesda, Maryland 20892.
J Biol Chem. 1988 Apr 5;263(10):4773-81.
Translocation of diphtheria toxin (DT) or ricin to the cytosol is the rate-limiting step responsible for (pseudo) first-order decline in protein synthesis observed in intoxicated cell populations. The requirements for energy utilization in the translocation of both toxins are examined by perturbing the intoxication during this period of protein synthesis decline. Translocation of either toxin is blocked at 4 degrees C and requires energy. Ricin translocation is tightly coupled to ATP hydrolysis with no involvement of membrane potential. Cell depolarization slows the rate of DT translocation but does not block completely. Elimination of transmembrane pH gradients alone does not affect DT translocation; however, in combination with depolarization, translocation is blocked virtually completely. Energy requirements for DT intoxication are mediated by establishing a plasma membrane potential and a pH gradient across some cellular membrane. It is proposed that a postendocytotic vesicle containing processed DT fuses with the plasma membrane. Either component of the proton motive force across the plasma membrane then drives DT translocation. Ricin apparently utilizes a different energy coupling mechanism at a different intracellular site, thus demonstrating toxin specificity in the translocation mechanism.
白喉毒素（DT）或蓖麻毒素向细胞质的转运是导致中毒细胞群体中蛋白质合成出现（伪）一级下降的限速步骤。通过在蛋白质合成下降期间干扰中毒过程，研究了两种毒素转运过程中能量利用的需求。两种毒素的转运在4℃时均被阻断且需要能量。蓖麻毒素的转运与ATP水解紧密偶联，与膜电位无关。细胞去极化会减缓DT的转运速率，但不会完全阻断。单独消除跨膜pH梯度不会影响DT的转运；然而，与去极化相结合时，转运几乎会完全被阻断。DT中毒的能量需求是通过在某些细胞膜上建立质膜电位和pH梯度来介导的。有人提出，含有加工后的DT的内吞后囊泡与质膜融合。然后，跨质膜的质子动力势的任何一个组成部分都会驱动DT的转运。蓖麻毒素显然在不同的细胞内位点利用了不同的能量偶联机制，从而在转运机制中表现出毒素特异性。
