The light chain but not the heavy chain of botulinum A toxin inhibits exocytosis from permeabilized adrenal chromaffin cells

The heavy and light chains of botulinum A toxin were separated by
anion exchange chromatography. Their intracellular actions were
studied using bovine adrenal chromaffin cells permeabilized with
streptolysin O. Purified light chain inhibited the Ca2+-stimulated
[3H]noradrenaline release with a half-maximal effect at about 1.8
nM. The inhibition was incomplete. Heavy chain up to 28 nM was
neither effective by itself nor did it enhance the inhibitory
effect of light chain. It is concluded that the light chain of
botulinum A toxin contains the functional domain responsible for
the inhibition of exocytosis.