Reductive chain separation of botulinum A toxin — a prerequisite to its inhibitory action on exocytosis in chromaffin cells

Cleavage of the disulfide bond linking the heavy and the light
chains of tetanus toxin is necessary for its inhibitory action on
exocytotic release ofcatecholamines from permeabi1ized chromaffin
cells [(1989) FEBS Lett. 242, 245-248; (1989) J. Neurochern., in
press]. The related botulinum A toxin also consists of a heavy and
a light chain linked by a disulfide bond. The actions ofboth
neurotoxins on exocytosis were presently compared using
streptolysin O-permeabilized bovine adrenal chromaffin cells.
Botulinum A toxin inhibited Ca2 +-stimulated catecholamine release
from these cells. Addition of dithiothreitollowered the effective
doses to values below 5 nM. Under the same conditions, the
effective doses of tetanus toxin were decreased by a factor of
five. This indicates that the interchain S-S bond of botulinum A
toxin must also be split before the neurotoxin can exert its effect
on exocytosis.