Erdal E, Bartels F, Binscheck T, Erdmann G, Frevert J, Kistner A, Weller U, Wever J, Bigalke H
PharmaTec GmbH, Flörsheim, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 1995 Jan;351(1):67-78. doi: 10.1007/BF00169066.
Tetanus and botulinum A neurotoxins were introduced into the cytosol of chromaffin cells by means of an electric field in which the plasma membrane is forced to form pores of approximately 1 micron at the sites facing the electrodes. As demonstrated by electron microscopy, both [125I] and gold-labelled tetanus toxin (TeTx) diffuse through these transient openings. Dichain-TeTx, with its light chain linked to the heavy chain by means of a disulfide bond, causes the block of exocytosis to develop more slowly than does the purified light chain. The disulfide bonds, which in both toxins hold the subunits together, were cleaved by the intrinsic thioredoxin-reductase system. Single chain TeTx, in which the heavy and light chains are interconnected by an additional peptide bond, was far less effective than dichain-TeTx at blocking exocytosis, which indicates that proteolysis is the rate-limiting step. The toxins were degraded further to low-molecular weight fragments which, together with intact toxins and subunits, were released by the cells. The intracellular half-life of [125I] dichain-TeTx was approximately three days. The number of light-chain molecules required to maintain exocytosis block in a single cell, as calculated by two different methods, was less than 10. The long duration of tetanus poisoning may result from the persistence of intracellular toxin due to scarcity of free cytosolic proteases. This may also hold for the slow recovery from botulism.
破伤风毒素和肉毒杆菌A神经毒素通过电场被导入嗜铬细胞的胞质溶胶中，在该电场中，质膜被迫在面对电极的部位形成直径约1微米的孔。电子显微镜显示，[125I]标记的和金标记的破伤风毒素（TeTx）都能通过这些瞬时开口扩散。二链TeTx的轻链通过二硫键与重链相连，其导致胞吐作用的阻断比纯化的轻链发展得更慢。两种毒素中使亚基结合在一起的二硫键被内在的硫氧还蛋白还原酶系统裂解。单链TeTx中重链和轻链通过一个额外的肽键相互连接，在阻断胞吐作用方面远不如二链TeTx有效，这表明蛋白水解是限速步骤。毒素进一步降解为低分子量片段，这些片段与完整的毒素和亚基一起被细胞释放。[125I]二链TeTx在细胞内的半衰期约为三天。通过两种不同方法计算得出，在单个细胞中维持胞吐作用阻断所需的轻链分子数少于10个。破伤风中毒的持续时间长可能是由于胞质溶胶中游离蛋白酶稀缺，导致细胞内毒素持续存在。肉毒中毒恢复缓慢可能也与此有关。
