When tetanus toxin from Clostridium tetani or IgA protease from Neisseria gonorrhoeae is translocated artificially into the cytosol of chromaffin cells, both enzymes inhibit calcium-induced exocytosis, which can be measured by changes in membrane capacitance. The block of exocytosis caused by both proteases cannot be reversed by enforced stimulation with increased calcium concentration. This effect differs from the botulinum A neurotoxin-induced block of exocytosis that can be overcome by elevation of the intracellular calcium concentration. Tetanus toxin is about 50-fold more potent than IgA protease in cells stimulated by carbachol. In this case, the release of [3H]noradrenaline was determined. Trypsin and endoprotease Glu-C are hardly effective and only at concentrations that disturb the integrity of the cells. Like tetanus toxin, IgA protease also splits synaptobrevin II, though at a different site of the molecule. However, unlike tetanus toxin, it does not cleave cellubrevin. It is concluded that the membranes of chromaffin vesicles contain synaptobrevin II, which, as in neurons, appears to play a crucial part in exocytosis.
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