Botulinum toxin and tetanus toxin recognize similar membrane determinants.

The binding fragment of tetanus toxin (50,000 dalton carboxy-terminus of heavy chain) does not block neuromuscular transmission, but it does antagonize the ability of native tetanus toxin to block neuromuscular transmission. The binding fragment of tetanus toxin also antagonizes certain botulinum toxins, including types C and E. Antagonism is at the cell surface, suggesting that the various molecules compete for a similar membrane binding site. The data indicate that the binding site is specific for botulinum toxin rather than tetanus toxin.