Characterization and visualization of tetanus toxin acceptors on adrenal chromaffin granules

Tetanus toxin (TT), a potent neurotoxin which blocks neurotransmitter release in neuronal systems, also inhibits Ca²⁺-induced catecholamine release from digitonin-permeabilized chromaffin cells. In searching for intracellular targets for the toxin we studied the binding of affinity-purified TT to bovine adrenal chromaffin granules. TT bound in a neuraminidase-sensitive fashion to intact granules and to isolated granule membranes, as assayed biochemically and visualized by electron microscopic techniques. The binding characteristics of the toxin to chromaffin granule membranes are very similar to the binding of TT to brain synaptosomal membranes. We suggest that the TT binding site is a glycoconjugate of the G1b type which is localized on the cytoplasmic face of the granule membrane and might be involved in exocytotic membrane fusion.