Binding to mouse brain synaptosomes of Clostridium botulinum type E derivative toxin before and after tryptic activation.

Clostridium botulinum type E125 I-labelled derivative toxin, both the partially active (intact) and the fully active (nicked) forms, bound to mouse brain synaptosomes. They gave the same KD and Bmax values in binding to synaptosomes, although the nicked form possessed a mouse lethal potency about 30 times higher than that of the intact form. These results may indicate that the binding site of the derivative toxin is not modified by tryptic activation and that the binding to synaptosomes is independent of the blockade of acetylcholine release.