Evidences for a Link between Proteolysis and the Inhibition of [3H]-Noradrenaline Release by the Light Chain of Tetanus Toxin
The mode of action of tetanus toxin (TeTx) light chain was studied on permeabilized bovine adrenomedullary cells in culture. Pretreatment with digitonin allowed free access of proteins together with other agents into the interior of the cell. Ca2+-evoked release of [3H]noradrenaline, basal outflow in the absence of Ca2+, and total content of radioactivity was measured.’ Light chain inhibited the release only. We then compared numerous enzymes to light chain with respect to the three parameters mentioned. Phospholipase A2 from Crotalus terrificus, C. botulinum C2 toxin together with NAD, and neuraminidase from V. cholerae were without effect. Some proteinases, for instance trypsin, chymotrypsin and papain, destroyed the cells as evident from the increased basal outflow and decrease of total content of radioactivity. Others such as thermolysin, collagenase from C. histolyticum, endoproteinase Lys-C or leucine amino peptidase were inactive in the range investigated. However, endoproteinase glu-C depressed the Ca2+-evoked release while it increased the basal outflow only slightly over a wide range of concentrations. This proteinase was about 10 times less potent than the light chain of TeTx. Thus light chain at least resembled a proteinase in its action on adrenomedullary cells, although it did hydrolyse none among the proteins and peptides tested. The putative substrate should be limited to neurons and adrenomedullary cells since exocytosis was not influenced in permeabilized pancreatic acinar cells (personal communication from I. Schulz, Institute of Physiology, Homburg/Saar). Searches for specific binding of 125I-labelled light chain to cultured cells or subcellular fractions from adrenal medulla were fruitless.
KeywordsLight Chain Pancreatic Acinar Cell Noradrenaline Release Tetanus Toxin Clostridium Botulinum
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